LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Micropower USB Power
Manager with Li-Ion Charger
and Two Step-Down Regulators
Description
Features
10μA Standby Mode Quiescent Current (All Outputs On)
n Seamless Transition Between Input Power Sources:
Li-Ion/Polymer Battery and USB
n 240mΩ Internal Ideal Diode
n Dual High Efficiency Step-Down Switching Regulators
(200mA IOUT) with Adjustable Output Voltages
n Pushbutton On/Off Control with System Reset
n Reset Time: 5 sec (LTC3554/LTC3554-1),
14 sec (LTC3554-2/LTC3554-3)
n Full Featured Li-Ion/Polymer Battery Charger
n Programmable Charge Current with Thermal Limiting
n Instant-On Operation with Discharged Battery
n Battery Float Voltage: 4.2V (LTC3554/LTC3554-2/
LTC3554-3), 4.1V (LTC3554-1)
n 3mm × 3mm × 0.75mm 20-Lead QFN Package
n
Applications
n
n
n
n
USB-Based Handheld Products
Portable Li-Ion/Polymer Based Electronic Devices
Fitness Computers
Low Power Medical Devices
The LTC®3554 family* are micropower, highly integrated
power management and battery charger ICs for single-cell
Li-Ion/Polymer battery applications. They include a
PowerPath™ manager with automatic load prioritization,
a battery charger, an ideal diode and numerous internal
protection features. Designed specifically for USB applications, the LTC3554 power managers automatically limit
input current to a maximum of either 100mA or 500mA.
Battery charge current is automatically reduced such that
the sum of the load current and the charge current does
not exceed the selected input current limit.
The LTC3554 also includes two synchronous step-down
switching regulators as well as a pushbutton controller.
With all supplies enabled in standby mode, the quiescent
current drawn from the battery is only 10μA. The LTC3554
family are available in a 3mm × 3mm × 0.75mm 20-lead
QFN package.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and PowerPath, Hot Swap and Bat-Track are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 6522118, 6700364, 5481178, 6304066, 6570372, 6580258, 7511390.
*See table on page 2 for available options.
Typical Application
10µF
100k
VBUS
NTC
100k
T
VOUT
SYSTEM
LOAD
10µF
PROG
BAT
HPWR
BVIN
1.87k
SUSP
+
14
Li-Ion
BATTERY
2.2µF
4.7µH
PWR_ON1
FSEL
FB1
PGOOD
10µF
10µH
1.2V
200mA
SW2
10pF
PBSTAT
ON/OFF
2.05M
649k
STBY
PWR_ON2
3.3V
200mA
SW1
10pF
ON
Battery Drain Current
vs Temperature
LTC3554 CHRG
FB2
332k
10µF
BATTERY DRAIN CURRENT (µA)
4.35V TO 5.5V
USB INPUT
VBAT = 3.8V
STBY = 3.8V
12 REGULATORS LOAD = 0mA
BOTH REGULATORS
10 ENABLED
8
6
4
ONE REGULATOR ENABLED
BOTH REGULATORS DISABLED
2
HARD RESET
0
–75 –50 –25 0
25 50 75
TEMPERATURE (°C)
100 125
3554 TA01b
649k
3554 TA01a
3554123ff
1
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Absolute Maximum Ratings
Pin Configuration
(Notes 1, 2, 3)
VBUS, VOUT, BVIN
t < 1ms and Duty Cycle < 1%.................... –0.3V to 7V
Steady State............................................. –0.3V to 6V
BAT, NTC, CHRG, SUSP, PBSTAT,
ON, PGOOD, FB1, FB2................................... –0.3V to 6V
PWR_ON1, PWR_ON2, STBY
HPWR, FSEL (Note 4).......................–0.3V to VCC + 0.3V
IBAT..............................................................................1A
ISW1, ISW2 (Continuous)....................................... 300mA
ICHRG , IPGOOD, IPBSTAT.............................................75mA
Operating Junction Temperature Range....–40°C to 85°C
Junction Temperature.............................................110°C
Storage Temperature Range................... –65°C to 125°C
PROG
BAT
VOUT
SUSP
VBUS
TOP VIEW
20 19 18 17 16
15 NTC
HPWR 1
FSEL 2
14 CHRG
21
GND
PBSTAT 3
PGOOD 4
13 SW1
12 BVIN
11 SW2
8
FB2
PWR_ON2
9 10
STBY
7
PWR_ON1
6
FB1
ON 5
UD PACKAGE
20-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 110°C, θJA = 58.7°C/W
EXPOSED PAD (PIN 21) IS GND, AND MUST BE SOLDERED TO PCB GND
Order Information
LEAD FREE FINISH
LTC3554EUD#PBF
TAPE AND REEL
LTC3554EUD#TRPBF
PART MARKING
LDYS
PACKAGE DESCRIPTION
20-Lead (3mm × 3mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
LTC3554EUD-1#PBF
LTC3554EUD-1#TRPBF
LGFG
20-Lead (3mm × 3mm) Plastic QFN
–40°C to 85°C
LTC3554EUD-2#PBF
LTC3554EUD-2#TRPBF
LFZX
20-Lead (3mm × 3mm) Plastic QFN
–40°C to 85°C
LTC3554EUD-3#PBF
LTC3554EUD-3#TRPBF
LGHK
20-Lead (3mm × 3mm) Plastic QFN
–40°C to 85°C
LTC3554EPD#PBF
LTC3554EPD#TRPBF
FDPT
20-Lead (3mm × 3mm) Plastic UTQFN
–40°C to 85°C (OBSOLETE)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
LTC3554 Options
PART NUMBER
FLOAT
VOLTAGE
HARD
RESET TIME SEQUENCING
LTC3554
4.2V
5 seconds
Yes (Buck1 → Buck2)
LTC3554-1
4.1V
5 seconds
Yes (Buck1 → Buck2)
LTC3554-2
4.2V
14 seconds Yes (Buck1 → Buck2)
LTC3554-3
4.2V
14 seconds No (Buck1 and Buck2
Together)
2
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
The
Power
Manager Electrical Characteristics l denotes specifications that
apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2), VBUS = 5V, VBAT = 3.8V,
HPWR = SUSP = PWR_ON1 = PWR_ON2 = 0V, RPROG = 1.87k, STBY = High, unless otherwise noted.
SYMBOL
PARAMETER
No-Load Quiescent Currents
Battery Drain Current
IBATQ
IBATQC
IBUSQ
Battery Drain Current, VBUS Available
VBUS Input Current
BVIN Input Current
Shutdown Input Current
One Buck Enabled, Standby Mode
Both Bucks Enabled, Standby Mode
One Buck Enabled
Both Bucks Enabled
Input Power Supply
VBUS
Input Supply Voltage
Total Input Current
IBUS(LIM)
IBVINQ
VUVLO
VBUS Undervoltage Lockout
VBUS to BAT Differential Undervoltage
Lockout
Input Current Limit Power FET
RON_ILIM
On-Resistance (Between VBUS and VOUT)
Battery Charger
VBAT Regulated Output Voltage
VFLOAT
VDUVLO
ICHG
VPROG
VPROG,TRKL
hPROG
ITRKL
VTRKL
Constant-Current Mode Charge Current
PROG Pin Servo Voltage
PROG Pin Servo Voltage in Trickle Charge
Ratio of IBAT to PROG Pin Current
Trickle Charge Current
Trickle Charge Threshold Voltage
ΔVRECHRG
tTERM
tBADBAT
hC/10
RON_CHG
Recharge Battery Threshold Voltage
Safety Timer Termination Period
Bad Battery Termination Time
End-of-Charge Indication Current Ratio
Battery Charger Power FET
On-Resistance (Between VOUT and BAT)
Junction Temperature in Constant
Temperature Mode
TLIM
NTC
VCOLD
VHOT
CONDITIONS
MIN
IOUT = 0 (Note 5)
VBUS = 0V (Hard Reset)
VBUS = 0V
VBUS = 0V, PWR_ON1 = PWR_ON2 = 3.8V
VBAT = VFLOAT, Timer Timed Out
100mA, 500mA Modes
SUSP = 5V (Suspend Mode)
VBVIN = 3.8V, VBUS = 0V (Note 8)
PWR_ON1 = STBY = 3.8V
PWR_ON1 = PWR_ON2 = STBY = 3.8V
PWR_ON1 = 3.8V, STBY = 0V
PWR_ON1 = PWR_ON2 = 3.8V, STBY = 0V
HPWR = 0V (100mA)
HPWR = 5V (500mA)
Rising Threshold
Falling Threshold
Rising Threshold
Falling Threshold
LTC3554/LTC3554-2/LTC3554-3
LTC3554/LTC3554-2/LTC3554-3, 0°C < TA < 85°C
LTC3554-1
LTC3554-1, 0°C < TA < 85°C
RPROG = 1.87k, 0 ≤ TA ≤ 85°C
l
l
4.35
80
400
3.5
0
4.179
4.165
4.079
4.065
380
VBAT < VTRKL
VBAT < VTRKL
VBAT Rising
VBAT Falling
Threshold Voltage Relative to VFLOAT
Timer Starts when VBAT = VFLOAT – 50mV
VBAT < VTRKL
(Note 6)
IBAT = 200mA
Cold Temperature Fault Threshold Voltage Rising NTC Voltage
Hysteresis
Hot Temperature Fault Threshold Voltage Falling NTC Voltage
Hysteresis
30
2.6
–75
3.2
0.4
0.085
TYP
MAX
UNITS
0.2
3
6.5
5
300
15
2
5
12
8
500
30
µA
µA
µA
µA
µA
µA
0.01
1.5
3
18
36
1
3
6
35
70
µA
µA
µA
µA
µA
5.5
100
500
3.9
V
mA
mA
V
V
mV
mV
mΩ
90
450
3.8
3.6
200
50
350
4.2
4.2
4.1
4.1
400
1
0.1
750
40
2.9
2.75
–100
4
0.5
0.1
220
300
4.221
4.235
4.121
4.135
420
50
3
–115
5
0.63
0.115
110
75
34
76
1.3
35
1.3
V
V
V
V
mA
V
V
mA/mA
mA
V
V
mV
Hour
Hour
mA/mA
mΩ
°C
77
36
%VBUS
%VBUS
%VBUS
%VBUS
3554123ff
3
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
The
POWER
MANAGER Electrical Characteristics l denotes specifications that
apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2), VBUS = 5V, VBAT = 3.8V,
HPWR = SUSP = PWR_ON1 = PWR_ON2 = 0V, RPROG = 1.87k, STBY = High, unless otherwise noted.
SYMBOL
VDIS
PARAMETER
NTC Disable Threshold Voltage
NTC Leakage Current
INTC
Ideal Diode
Forward Voltage Detection
VFWD
RDROPOUT Diode On-Resistance, Dropout
Diode Current Limit
IMAX
Logic Inputs (HPWR, SUSP)
Input Low Voltage
VIL
Input High Voltage
VIH
Internal Pull-Down Resistance
RPD
Logic Output (CHRG)
Output Low Voltage
VOL
Output Hi-Z Leakage Current
ICHRG
CONDITIONS
Falling NTC Voltage
Hysteresis
VNTC = VBUS = 5V
l
MIN
1.2
TYP
1.7
50
–50
(Note 12)
IOUT = 200mA, VBUS = 0V
(Note 7)
MAX
2.2
50
15
240
1
mV
mΩ
A
0.4
V
V
MΩ
250
1
mV
µA
1.2
4
ICHRG = 5mA
VBAT = 4.5V, VCHRG = 5V
65
0
UNITS
%VBUS
mV
nA
Switching
Regulator Electrical Characteristics l denotes
The
specifications that apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2).
VOUT = BVIN = 3.8V, PWR_ON1 = PWR_ON2 = 0V, unless otherwise noted.
SYMBOL
PARAMETER
BVIN
Input Supply Voltage
VOUT UVLO VOUT Falling
VOUT Rising
fOSC
Oscillator Frequency
CONDITIONS
(Note 9)
BVIN Connected to VOUT Through Low
Impedance. VOUT UVLO Disables the Switching
Regulators.
FSEL High
FSEL Low
FB1 Input Current (Note 8)
IFB1
IFB2
FB2 Input Current (Note 8)
SW1 Pull-Down in Shutdown
PWR_ON1 = 0V
RSW1_PD
RSW2_PD
SW2 Pull-Down in Shutdown
PWR_ON2 = 0V
Logic Input Pins (FSEL, STBY)
Input High Voltage
Input Low Voltage
Input Current
Switching Regulator 1 in Normal Operation (STBY Low)
Peak PMOS Current Limit
PWR_ON1 = 3.8V (Note 7)
ILIM1
Regulated Feedback Voltage
PWR_ON1 = 3.8V
VFB1
D1
Max Duty Cycle
RDS(ON) of PMOS
ISW1 = 100mA
RP1
RDS(ON) of NMOS
ISW1 = –100mA
RN1
Switching Regulator 1 in Standby Mode (STBY High)
PWR_ON1 = 3.8V, VFB1 Falling
VFB1_LOW Feedback Voltage Threshold
ISHORT1_SB Short-Circuit Current
PWR_ON1 = 2.9V, ISW1 = 5mA, VFB1 = 0.77V,
VDROP1_SB Standby Mode Dropout Voltage
VOUT = 2.9V, BVIN = 2.9V
4
l
MIN
2.7
2.5
TYP
1.91
0.955
–0.05
–0.05
2.25
1.125
2.6
2.8
MAX
5.5
2.9
2.59
1.295
0.05
0.05
10
10
1.2
0.4
1
–1
l
300
780
100
450
800
770
10
800
21
25
MHz
MHz
µA
µA
kΩ
kΩ
V
V
µA
600
820
mA
mV
%
Ω
Ω
820
50
60
mV
mA
mV
1.1
0.7
l
UNITS
V
V
V
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Switching
Regulator Electrical Characteristics l denotes
The
specifications that apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2).
VOUT = BVIN = 3.8V, PWR_ON1 = PWR_ON2 = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
Switching Regulator 2 in Normal Operation (STBY Low)
Peak PMOS Current Limit
PWR_ON2 = 3.8V (Note 7)
ILIM2
l
Regulated Feedback Voltage
PWR_ON2 = 3.8V
VFB2
D2
Max Duty Cycle
RDS(ON) of PMOS
ISW2 = 100mA
RP2
RDS(ON) of NMOS
ISW2 = –100mA
RN2
Switching Regulator 2 in Standby Mode (STBY High)
l
PWR_ON2 = 3.8V, VFB2 Falling
VFB2_LOW Feedback Voltage Threshold
ISHORT2_SB Short-Circuit Current
PWR_ON2 = 2.9V, ISW2 = 5mA, VFB2 = 0.77V, VOUT
VDROP2_SB Standby Mode Dropout Voltage
= 2.9V, BVIN = 2.9V
MIN
TYP
MAX
UNITS
300
780
100
450
800
600
820
mA
mV
%
Ω
Ω
820
50
60
mV
mA
mV
1.1
0.7
770
10
800
21
25
PUSHBUTTON
INTERFACE Electrical Characteristics l denotes
The
specifications that apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2).
VBAT = 3.8V, unless otherwise noted.
SYMBOL
PARAMETER
Pushbutton Pin (ON)
Pushbutton Operating Supply Range
VCC_PB
ON Threshold Rising
VON_TH
ON Threshold Falling
CONDITIONS
ON Input Current
ION
Pushbutton Pull-Up Resistance
RPB_PU
Logic Input Pins (PWR_ON1, PWR_ON2)
VPWR_ONx PWR_ONx Threshold Rising
PWR_ONx Threshold Falling
VON = VCC (Note 4)
Pull-Up to VCC (Note 4)
PWR_ONx Input Current
IPWR_ONx
Status Output Pins (PBSTAT, PGOOD)
PBSTAT Output High Leakage Current
IPBSTAT
PBSTAT Output Low Voltage
VPBSTAT
PGOOD Output High Leakage Current
IPGOOD
PGOOD Output Low Voltage
VPGOOD
VTHPGOOD PGOOD Threshold Voltage
Pushbutton Timing Parameters (Note 11)
tON_PBSTATL Minimum ON Low Time to Cause PBSTAT
Low
Delay from ON High to PBSTAT High
tON_
PBSTATH
tON_PUP
tON_HR
Minimum ON Low Time to Enter
Power-Up (PUP1 or PUP2) State
Minimum ON Low Time to Hard Reset
tPBSTAT_PW PBSTAT Minimum Pulse Width
(Notes 4 , 9)
MIN
l
TYP
2.7
0.4
–1
200
5.5
1.2
400
ON Brought Low During Power-On (PON) or
Power-Up (PUP1, PUP2) States
Power-On (PON) State, After PBSTAT Has Been
Low for at Least tPBSTAT_PW
Starting in the Hard Reset (HR) or Power-Off
(POFF) States
ON Brought Low During the Power-On (PON)or
Power-Up (PUP1, PUP2) States
LTC3554/LTC3554-1
LTC3554-2/LTC3554-3
Power-On (PON) or Power-Up (PUP1, PUP2)
States
1
–1
0.1
–1
0.1
–8
4
11
40
1
650
1.2
0.4
–1
VPBSTAT = 3V
IPBSTAT = 3mA
VPGOOD = 3V
IPGOOD = 3mA
(Note 10)
MAX
1
0.4
1
0.4
UNITS
V
V
V
µA
kΩ
V
V
µA
µA
V
µA
V
%
50
ms
900
µs
400
ms
5
14
50
6
17
s
s
ms
3554123ff
5
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
PUSHBUTTON
INTERFACE Electrical Characteristics l denotes
The
specifications that apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2).
VBAT = 3.8V, unless otherwise noted.
SYMBOL
tEXTPWR
tPON_UP
PARAMETER
Power-Up from USB Present to Power-Up
(PUP1 or PUP2) State
Any PWR_ONx High to Power-On State
tPGOODH
PWR_ONx Low to Buckx Disabled
Power-Up (PUP1 or PUP2) State Duration
Power-Down (PDN1 or PDN2) State
Duration
Bucks in Regulation to PGOOD High
tPGOODL
Bucks Disabled to PGOOD Low
tPON_DIS
tPUP
tPDN
CONDITIONS
Starting in the Hard Reset (HR) or Power-Off
(POFF) States
Starting with Both PWR_ONx Low in the PowerOff (POFF) State
All Enabled Bucks within PGOOD Threshold
Voltage
All Bucks Disabled
Note 1. Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3554 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC3554 are guaranteed to meet specifications from
0°C to 85°C junction temperature. Specifications over the –40°C to
85°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. Note that
the maximum ambient temperature consistent with these specifications
is determined by specific operating conditions in conjunction with board
layout, the rated package thermal impedance and other environmental
factors.
The junction temperature (TJ, in °C) is calculated from the ambient
temperature (TA, in °C) and power dissipation (PD, in Watts) according to
the formula:
TJ = TA + (PD • qJA)
where qJA (in °C/W) is the package thermal impedance.
Note 3. This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperatures will exceed 110°C when overtemperature protection is
active. Continuous operation above the specified maximum operating
junction temperature may result in device degradation or failure.
6
MIN
TYP
100
MAX
UNITS
ms
900
µs
1
5
1
µs
s
s
230
ms
100
µs
Note 4. VCC is the greater of VBUS or BAT.
Note 5. Total Battery Drain Current is the sum of IBATQ and IOUT. For
example, in applications where the buck input (BVIN pin) is connected to
the PowerPath output (VOUT pin) such that IOUT = IBVIN, total battery drain
current = IBATQ + IBVIN.
Note 6. hC/10 is expressed as a fraction of programmed full charge
current with specified PROG resistor.
Note 7. The current limit features of this part are intended to protect the
IC from short term or intermittent fault conditions. Continuous operation
above the absolute maximum specified pin current rating may result in
device degradation or failure.
Note 8. FB High, Not Switching
Note 9. VOUT not in UVLO.
Note 10. PGOOD threshold is expressed as a percentage difference from
the buck regulation voltage. The threshold is measured with the buck
feedback pin voltage rising.
Note 11. See the Operation section of this data sheet for detailed
explanation of the pushbutton state machine and the effects of each state
on switching regulator and power manager operation.
Note 12. If VBUS < VUVLO then VFWD = 0 and the forward voltage across
the ideal diode is equal to its current times RDROPOUT.
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Typical Performance Characteristics
400
VBUS Supply Current
vs Temperature (Suspend Mode)
25
VBUS = 5V
HPWR = L
15
IBUS (µA)
IBUS (µA)
14
300
10
250
5
200
–75 –50 –25
0
–75 –50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
VBAT = 3.8V
STBY = 3.8V
12 REGULATORS LOAD = 0mA
VBUS = 5V
20
350
BOTH REGULATORS
10 ENABLED
8
ONE REGULATOR ENABLED
6
BOTH REGULATORS DISABLED
4
2
HARD RESET
0
–75 –50 –25 0
25 50 75
TEMPERATURE (°C)
0 25 50 75 100 125 150
TEMPERATURE (°C)
Battery Drain Current
vs Temperature (Suspend Mode)
3554 G03
VBUS Current Limit
vs Temperature
500
VBUS = 5V
VBAT = 3.8V
4
400
3
300
VBUS and Battery Current
vs Load Current
600
VBUS = 5V
RPROG = 1.87k
500
HPWR = H
IVBUS
200
100
1
0
–75 –50 –25
CURRENT (mA)
IVBUS (mA)
IBAT (µA)
400
2
0
–75 –50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
0
0
25 50 75
TEMPERATURE (°C)
0.45
200
300
400
LOAD CURRENT (mA)
500
Battery Charge Current and
Voltage vs Time
(LTC3554/LTC3554-2/LTC3554-3)
BATTERY CURRENT (mA)
IBAT (mA)
6
240
80 VBUS = 5V
HPWR = H
RPROG = 1.87k
0
–75 –50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
3554 G06
CHRG
5
VBAT
400
4
300
200
100
0
3
SAFETY TIMER
TERMINATION
C/10
0
1
2
2
VOLTAGE (V)
3554 G05a
100
920mAhr CELL
VBUS = 5V
500 RPROG = 1.87k
160
0 25 50 75 100 125 150
TEMPERATURE (°C)
0
600
320
0.25
IBAT
(DISCHARGING)
3554 G05
400
0.40
RON (Ω)
–100
100 125
480
0.30
IBAT
(CHARGING)
100
Charge Current vs Temperature
(Thermal Regulation)
IOUT = 200mA
0.20
–75 –50 –25
200
3554 G04
RON from VBUS to VOUT
vs Temperature
0.35
ILOAD
300
HPWR = L
3554 G03b
0.50
100 125
3554 G02
3554 G01
5
Battery Drain Current
vs Temperature
BATTERY DRAIN CURRENT (µA)
VBUS Supply Current
vs Temperature
TA = 25°C, unless otherwise specified.
1
IBAT
3
5
4
TIME (hour)
6
7
8
0
3554 G07
3554123ff
7
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Typical Performance Characteristics
4.22
VBUS = 5V
HPWR = H
4.20
VFLOAT (V)
4.12
4.16
4.14
4.12
LTC3554-1
LTC3554-1
4.08
–75 –50 –25
0
25 50 75
TEMPERATURE (°C)
3554 G08
VBUS
250
VFWD (mV)
VBUS = 5V
5V
150
IBUS
0.5A/DIV 0A
VBUS = 0V
100
VOUT
0
3.2
3.6
VBAT (V)
4
5V
0
5V
1ms/DIV
50µs/DIV
3554 G12
VBAT = 3.75V
IOUT = 100mA
RPROG = 2k
1200
4.4
IBAT
0.5A/DIV 0A
50
1000
2.8
0
IBUS
0A
0.5A/DIV
IBAT 0A
0.5A/DIV
600
800
IBAT (mA)
2.4
3554 G10
VBUS
0
VOUT
400
2
VBUS Disconnect Waveform
5V
200
200
0
100 125
VBUS Connect Waveform
300
0
200
3554 G09
Forward Voltage
vs Ideal Diode Current
0
300
100
4.10
50 100 150 200 250 300 350 400 450
IBAT (mA)
0
VBUS = 5V
HPWR = H
RPROG = 1.87k
400
LTC3554/LTC3554-2/LTC3554-3
4.14
4.08
500
4.18
4.16
4.10
IBAT vs VBAT
(LTC3554/LTC3554-2/LTC3554-3)
VBUS = 5V
IBAT = 2mA
4.20
LTC3554/LTC3554-2/LTC3554-3
4.18
VFLOAT (V)
Battery Regulation (Float)
Voltage vs Temperature
VFLOAT Load Regulation
IBAT (mA)
4.22
TA = 25°C, unless otherwise specified.
3554 G13
VBAT = 3.75V
IOUT = 100mA
RPROG = 2k
3554 G11
Switching from 100mA Mode to
500mA Mode
Switching from Suspend Mode to
500mA Mode
Oscillator Frequency
vs Temperature
2.6
IBUS
0.5A/DIV
5V
0
VOUT
5V
0
5V
0
IBUS
0A
0.5A/DIV
0A
IBAT
0.5A/DIV 0A
IBAT
0A
0.5A/DIV
1ms/DIV
VBAT = 3.75V
IOUT = 50mA
RPROG = 2k
3554 G14
1ms/DIV
VBAT = 3.75V
IOUT = 50mA
RPROG = 2k
3554 G15
OSCILLATOR FREQUENCY (MHz)
HPWR
SUSP
2.5
2.7V
3.8V
5.5V
2.4
2.3
2.2
2.1
2.0
1.9
–75 –50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3554 G16
8
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Typical Performance Characteristics
100
Step-Down Switching Regulator 1
3.3V Output Efficiency vs IOUT1
Step-Down Switching Regulator 1
2.5V Output Efficiency vs IOUT1
80
70
70
70
40
30
EFFICIENCY (%)
80
50
60
50
40
30
3.8V
5V
0
0.01
0.1
1
10
IOUT1 (mA)
100
3.8V
5V
10
0
0.01
1000
0.1
1
10
IOUT1 (mA)
100
35
30
BVIN SUPPLY CURRENT (µA)
EFFICIENCY (%)
70
60
50
40
30
20
0
0.01
0.1
1
10
IOUT2 (mA)
100
NO LOAD
STBY = L
–45°C
25°C
90°C
25
20
15
10
5
3.8V
5V
10
0
2.5
1000
3
3.5
4
4.5
5
BVIN SUPPLY VOLTAGE (V)
3554 G25
SHORT CIRCUIT CURRENT (mA)
0.1
1
10
IOUT2 (mA)
100
5.5
1000
Standby Mode BVIN Supply
Current Per Enabled Step-Down
Switching Regulator
3.0
2.5
NO LOAD
STBY = H
–45°C
25°C
90°C
2.0
1.5
1.0
0.5
0
2.5
3
3.5
4
4.5
5
BVIN SUPPLY VOLTAGE (V)
3554 G17
Step-Down Switching Regulator
Short-Circuit Current
vs Temperature
500
3.8V
5V
3554 G32
Burst Mode® BVIN Supply Current
Per Enabled Step-Down Switching
Regulator
FSEL = L
STBY = L
80
30
3554 G31
Step-Down Switching Regulator 2
1.2V Output Efficiency vs IOUT2
90
40
0
0.01
1000
3554 G24a
100
50
10
BVIN SUPPLY CURRENT (µA)
10
60
20
20
20
FSEL = L
STBY = L
90
80
60
Step-Down Switching Regulator 2
1.8V Output Efficiency vs IOUT2
100
FSEL = L
STBY = L
90
EFFICIENCY (%)
EFFICIENCY (%)
100
FSEL = L
STBY = L
90
TA = 25°C, unless otherwise specified.
5.5
3554 G18
Step-Down Switching Regulator
Output Transient
Step-Down Switching Regulator
Output Transient
STBY = L
480
460
440
VOUT2
20mV/DIV
(AC)
VOUT1
100mV/DIV
(AC)
5mA
150mA
IOUT1
5mA
IOUT2
10µA
420
400
–75 –50 –25
50µs/DIV
0 25 50 75 100 125 150
TEMPERATURE (°C)
VOUT2 = 1.2V
STBY = H
200µs/DIV
3554 G26
3554 G27
VOUT1 = 3.3V
STBY = L
3554 G19
3554123ff
9
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Typical Performance Characteristics
Step-Down Switching
Regulator Feedback Voltage
vs Output Current
Step-Down Switching
Regulator Switch Impedance
vs Temperature
1.6
1.4
0.815
PMOS
1.2
FEEDBACK VOLTAGE (V)
SWITCH IMPEDANCE (Ω)
0.820
BVIN = 3.2V
STBY = L
1.0
NMOS
0.8
TA = 25°C, unless otherwise specified.
0.6
0.4
Step-Down Switching Regulator
Start-Up Waveform
VOUT2
50mV/DIV
(AC)
3.8V
5V
STBY = L
0.810
VOUT1
1V/DIV
0.805
0V
IL1
100mA/DIV
0mA
PWR_ON1
0.800
0.795
0.790
100µs/DIV
0.785
0.2
0
–75 –50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
0.780
0.1
1
10
100
OUTPUT CURRENT (mA)
VOUT2 = 1.2V
IOUT2 = 50mA
ROUT1 = 22Ω
STBY = L
1000
3554 G21
3554 G20
Step-Down Switching
Regulator Output Transient
(FSEL Low to High)
Step-Down Switching Regulator
Dropout Voltage in Standby Mode
vs Load Current
Step-Down Switching
Regulator Output Transient (STBY
High to Low)
200
STBY
FSEL
50µs/DIV
VOUT1 = 3.3V
IOUT1 = 100mA
VOUT2 = 1.2V
IOUT2 = 50mA
STBY = L
10
DROPOUT VOLTAGE (mV)
VOUT2
20mV/DIV
(AC)
VOUT2
20mV/DIV
(AC)
VBVIN = 2.9V
VFBx = 780mV
–45°C
25°C
90°C
STBY = H
180
VOUT1
20mV/DIV
(AC)
VOUT1
50mV/DIV
(AC)
3554 G28
3554 G29
50µs/DIV
VOUT1 = 3.3V
IOUT1 = 5mA
VOUT2 = 1.2V
IOUT2 = 5mA
3554 G30
160
140
120
100
80
60
40
20
0
0
2
4
6
8
10
12
LOAD CURRENT (mA)
14
3554 G23
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Pin Functions
HPWR (Pin 1): High Power Logic Input. When this pin is
low the input current limit is set to 100mA and when this
pin is driven high it is set to 500mA. The SUSP pin needs
to be low for the input current limit circuit to be enabled.
This pin has a conditional internal pull-down resistor when
power is applied to the VBUS pin.
FSEL (Pin 2): Buck Frequency Select. When this pin is
low the buck switching frequency is set to 1.125MHz and
when this pin is driven high it is set to 2.25MHz.
PBSTAT (Pin 3): Pushbutton Status. This open-drain output
is a debounced and buffered version of the ON pushbutton input. It may be used to interrupt a microprocessor.
PGOOD (Pin 4): Power Good. This open-drain output
indicates that all enabled buck regulators have been in
regulation for at least 230ms.
ON (Pin 5): Pushbutton Input. Weak internal pull-up
forces a high state if ON is left floating. A normally open
pushbutton is connected from ON to ground to force a
low state on this pin.
FB1 (Pin 6): Feedback Input for Step-Down Switching
Regulator 1. This pin servos to a fixed voltage of 0.8V
when the control loop is complete.
FB2 (Pin 7): Feedback Input for Step-Down Switching
Regulator 2. This pin servos to a fixed voltage of 0.8V
when the control loop is complete.
PWR_ON2 (Pin 8): Logic Input Enables Step-Down Switching Regulator 2.
PWR_ON1 (Pin 9): Logic Input Enables Step-Down Switching Regulator 1.
STBY (Pin 10): Standby Mode. When this pin is driven
high the part enters a very low quiescent current mode.
The buck regulators are each limited to 5mA maximum
load current in this mode.
SW2 (Pin 11): Power Transmission (Switch) Pin for StepDown Switching Regulator 2.
BVIN (Pin 12): Power Input for Step-Down Switching
Regulators 1 and 2. It is recommended that this pin be
connected to the VOUT pin. It should be bypassed with a
low impedance multilayer ceramic capacitor.
SW1 (Pin 13): Power Transmission (Switch) Pin for StepDown Switching Regulator 1.
CHRG (Pin 14): Open-Drain Charge Status Output. This pin
indicates the status of the battery charger. It is internally
pulled low while charging. Once the battery charge current reduces to less than one-tenth of the programmed
charge current, this pin goes into a high impedance state.
An external pull-up resistor and/or LED is required to
provide indication.
NTC (Pin 15): The NTC pin connects to a battery’s thermistor to determine if the battery is too hot or too cold to
charge. If the battery’s temperature is out of range, charging
is paused until it drops back into range. A low drift bias
resistor is required from VBUS to NTC and a thermistor is
required from NTC to ground. If the NTC function is not
desired, the NTC pin should be grounded.
PROG (Pin 16): Charge Current Program and Charge
Current Monitor Pin. Connecting a resistor from PROG to
ground programs the charge current as given by:
I CHG (A)=
750V
RPROG
If sufficient input power is available in constant-current
mode, this pin servos to 1V. The voltage on this pin always
represents the actual charge current.
BAT (Pin 17): Single-Cell Li-Ion Battery Pin. Depending
on available power and load, a Li-Ion battery on BAT will
either deliver system power to VOUT through the ideal
diode or be charged from the battery charger.
VOUT (Pin 18): Output Voltage of the PowerPath Controller and Input Voltage of the Battery Charger. The majority
of the portable products should be powered from VOUT.
3554123ff
11
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Pin Functions
The LTC3554 will partition the available power between
the external load on VOUT and the internal battery charger.
Priority is given to the external load and any extra power
is used to charge the battery. An ideal diode from BAT to
VOUT ensures that VOUT is powered even if the load exceeds
the allotted input current from VBUS or if the VBUS power
source is removed. VOUT should be bypassed with a low
impedance multilayer ceramic capacitor.
SUSP (Pin 19): Suspend Mode Logic Input. If this pin
is driven high the input current limit path is disabled.
In this state the circuit draws negligible power from the
VBUS pin. Any load at the VOUT pin is provided by the
12
battery through the internal ideal diode. When this input
is grounded, the input current limit will be set to desired
value as determined by the state of the HPWR pin. This
pin has a conditional internal pull-down resistor when
power is applied to the VBUS pin.
VBUS (Pin 20): USB Input Voltage. VBUS will usually be
connected to the USB port of a computer or a DC output
wall adapter. VBUS should be bypassed with a low impedance multilayer ceramic capacitor.
GND (Exposed Pad Pin 21): Ground. The exposed package pad is ground and must be soldered to the PC board
for proper functionality and for maximum heat transfer.
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Block Diagram
18 VOUT
VBUS 20
HPWR
INPUT
CURRENT
LIMIT
1
SUSP 19
CC/CV
CHARGER
17 BAT
16 PROG
EXTPWR UVLO
NTC 15
BATTERY
TEMP
MONITOR
OSC
0.8V
CHRG 14
13 SW1
CHARGE
STATUS
EN
STBY
6
FB1
200mA STEP-DOWN DC/DC
FSEL
2
2.25MHz/
1.125MHz
OSCILLATOR
12 BVIN
OSC
0.8V
÷
4096
11 SW2
EN
STBY
STBY 10
7
FB2
4
PGOOD
200mA STEP-DOWN DC/DC
PWR_ON1
9
PWR_ON2
8
PBSTAT
3
ON
5
PUSH BUTTON
INTERFACE
POWER GOOD
COMPARATORS
21
3554 BD1
GND
3554123ff
13
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPeration
Introduction
The LTC3554 is a highly integrated power management
IC that includes the following features:
standby mode which can be used to power essential
keep-alive circuitry while draining ultralow current from
the battery for extended battery life.
PowerPath controller
USB PowerPath Controller
Battery charger
The input current limit and charger control circuits of
the LTC3554 are designed to limit input current as well
as control battery charge current as a function of IVOUT.
VOUT drives the combination of the external load, the two
step-down switching regulators and the battery charger.
Ideal diode
Pushbutton controller
Two step-down switching regulators
Designed specifically for USB applications, the PowerPath
controller incorporates a precision input current limit
which communicates with the battery charger to ensure
that input current never violates the USB specifications.
The ideal diode from BAT to VOUT guarantees that ample
power is always available to VOUT even if there is insufficient
or absent power at VBUS. The LTC3554 also includes a
pushbutton input to control the two synchronous stepdown switching regulators and system reset. The two
constant-frequency current mode step-down switching
regulators provide 200mA each and support 100% duty
cycle operation as well as operating in Burst Mode operation
for high efficiency at light load. No external compensation
components are required for the switching regulators.
Either regulator can be programmed for a minimum output voltage of 0.8V and can be used to power a microcontroller core, microcontroller I/O, memory or other
logic circuitry. The buck regulators can be operated at
1.125MHz or 2.25MHz. They also include a low power
If the combined load does not exceed the programmed
input current limit, VOUT will be connected to VBUS through
an internal 350mΩ P-channel MOSFET. If the combined
load at VOUT exceeds the programmed input current limit,
the battery charger will reduce its charge current by the
amount necessary to enable the external load to be satisfied
while maintaining the programmed input current. Even if
the battery charge current is set to exceed the allowable
USB current, the average input current USB specification
will not be violated. Furthermore, load current at VOUT will
always be prioritized and only excess available current will
be used to charge the battery.
The input current limit is programmed by the HPWR and
SUSP pins. If SUSP pin set high, the input current limit
is disabled. If SUSP pin is low, the input current limit is
enabled. HPWR pin selects between 100mA input current
limit when it is low and 500mA input current limit when
it is high.
Simplified PowerPath Block Diagram
VBUS 20
18 VOUT
CC/CV
CHARGER
+
–
100mA/500mA
INPUT CURRENT
LIMIT
IDEAL
15mV
17 BAT
3554 F01
14
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPeration
Ideal Diode From BAT to VOUT
Battery Charger
The LTC3554 has an internal ideal diode from BAT to VOUT
designed to respond quickly whenever VOUT drops below
BAT. If the load increases beyond the input current limit,
additional current will be pulled from the battery via the ideal
diode. Furthermore, if power to VBUS (USB) is removed,
then all of the application power will be provided by the
battery via the ideal diode. The ideal diode is fast enough
to keep VOUT from dropping significantly with just the
recommended output capacitor. The ideal diode consists
of a precision amplifier that enables an on-chip P-channel
MOSFET whenever the voltage at VOUT is approximately
15mV (VFWD) below the voltage at BAT. The resistance of
the internal ideal diode is approximately 240mΩ.
The LTC3554 includes a constant-current/constant-voltage battery charger with automatic recharge, automatic
termination by safety timer, low voltage trickle charging,
bad cell detection and thermistor sensor input for out of
temperature charge pausing. When a battery charge cycle
begins, the battery charger first determines if the battery
is deeply discharged. If the battery voltage is below VTRKL,
typically 2.9V, an automatic trickle charge feature sets the
battery charge current to 10% of the programmed value. If
the low voltage persists for more than 1/2 hour, the battery
charger automatically terminates. Once the battery voltage
is above 2.9V, the battery charger begins charging in full
power constant current mode. The current delivered to
the battery will try to reach 750V/RPROG. Depending on
available input power and external load conditions, the
battery charger may or may not be able to charge at the
full programmed current. The external load will always be
prioritized over the battery charge current. The USB current limit programming will always be observed and only
additional current will be available to charge the battery.
When system loads are light, battery charge current will
be maximized.
Suspend Mode
When the SUSP pin is pulled high the LTC3554 enters
suspend mode to comply with the USB specification. In
this mode, the power path between VBUS and VOUT is put
in a high impedance state to reduce the VBUS input current
to 15μA. The system load connected to VOUT is supplied
through the ideal diode connected to BAT.
VBUS Undervoltage Lockout (UVLO) and Undervoltage
Current Limit (UVCL)
An internal undervoltage lockout circuit monitors VBUS
and keeps the input current limit circuitry off until VBUS
rises above the rising UVLO threshold (3.8V) and at least
200mV above VBAT. Hysteresis on the UVLO turns off the
input current limit circuitry if VBUS drops below 3.6V or
within 50mV of VBAT. When this happens, system power at
VOUT will be drawn from the battery via the ideal diode. To
minimize the possibility of oscillation in and out of UVLO
when using resistive input supplies, the input current limit
is reduced as VBUS falls below 4.45V typical.
Charge Termination
The battery charger has a built-in safety timer. When the
battery voltage approaches the float voltage (4.2V for
LTC3554/LTC3554-2/LTC3554-3 or 4.1V for LTC3554-1),
the charge current begins to decrease as the LTC3554
enters constant-voltage mode. Once the battery charger
detects that it has entered constant-voltage mode, the four
hour safety timer is started. After the safety timer expires,
charging of the battery will terminate and no more current
will be delivered to the battery.
3554123ff
15
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPeration
Automatic Recharge
After the battery charger terminates, it will remain off
drawing only microamperes of current from the battery.
If the portable product remains in this state long enough,
the battery will eventually self discharge. To ensure that the
battery is always topped off, a charge cycle will automatically begin when the battery voltage falls below VRECHRG
(typically 4.1V for LTC3554/LTC3554-2/LTC3554-3 or 4V
for LTC3554-1). In the event that the safety timer is running
when the battery voltage falls below VRECHRG, the timer
will reset back to zero. To prevent brief excursions below
VRECHRG from resetting the safety timer, the battery voltage must be below VRECHRG for approximately 2ms. The
charge cycle and safety timer will also restart if the VBUS
UVLO cycles low and then high (e.g., VBUS, is removed
and then replaced).
Charge Current
The charge current is programmed using a single resistor
from PROG to ground. 1/750th of the battery charge current is delivered to PROG which will attempt to servo to
1.000V. Thus, the battery charge current will try to reach
750 times the current in the PROG pin. The program
resistor and the charge current are calculated using the
following equations:
R PROG =
750V
750V
,I CHG =
I CHG
R PROG
In either the constant-current or constant-voltage charging modes, the PROG pin voltage will be proportional to
the actual charge current delivered to the battery. Therefore, the actual charge current can be determined at any
time by monitoring the PROG pin voltage and using the
following equation:
I BAT =
16
V PROG
• 750
R PROG
In many cases, the actual battery charge current, IBAT, will
be lower than ICHG due to limited input current available
and prioritization with the system load drawn from VOUT.
Thermal Regulation
To prevent thermal damage to the IC or surrounding
components, an internal thermal feedback loop will
automatically decrease the programmed charge current
if the die temperature rises to approximately 110°C.
Thermal regulation protects the LTC3554 from excessive
temperature due to high power operation or high ambient
thermal conditions and allows the user to push the limits
of the power handling capability with a given circuit board
design without risk of damaging the LTC3554 or external
components. The benefit of the LTC3554 thermal regulation loop is that charge current can be set according to the
desired charge rate rather than worst-case conditions with
the assurance that the battery charger will automatically
reduce the current in worst-case conditions.
Charge Status Indication
The CHRG pin indicates the status of the battery charger. An
open-drain output, the CHRG pin can drive an indicator LED
through a current limiting resistor for human interfacing or
simply a pull-up resistor for microprocessor interfacing.
When charging begins, CHRG is pulled low and remains
low for the duration of a normal charge cycle. When charging is complete, i.e., the charger enters constant-voltage
mode and the charge current has dropped to one-tenth
of the programmed value, the CHRG pin is released (high
impedance). The CHRG pin does not respond to the C/10
threshold if the LTC3554 reduces the charge current due
to excess load on the VOUT pin. This prevents false end
of charge indications due to insufficient power available
to the battery charger. Even though charging is stopped
during an NTC fault the CHRG pin will stay low indicating
that charging is not complete.
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPeration
Battery Charger Stability Considerations
The LTC3554’s battery charger contains both a constantvoltage and a constant-current control loop. The constantvoltage loop is stable without any compensation when a
battery is connected with low impedance leads. Excessive
lead length, however, may add enough series inductance
to require a bypass capacitor of at least 1μF from BAT to
GND. Furthermore, a 100μF 1210 ceramic capacitor in
series with a 0.3Ω resistor from BAT to GND is required
to keep ripple voltage low if operation with the battery
disconnected is allowed.
High value, low ESR multilayer ceramic chip capacitors
reduce the constant-voltage loop phase margin, possibly
resulting in instability. Ceramic capacitors up to 22μF
may be used in parallel with a battery, but larger ceramics
should be decoupled with 0.2Ω to 1Ω of series resistance.
In constant-current mode, the PROG pin is in the feedback loop rather than the battery voltage. Because of the
additional pole created by any PROG pin capacitance,
capacitance on this pin must be kept to a minimum. With
no additional capacitance on the PROG pin, the battery
charger is stable with program resistor values as high
as 25k. However, additional capacitance on this node
reduces the maximum allowed program resistor. The pole
frequency at the PROG pin should be kept above 100kHz.
Therefore, if the PROG pin has a parasitic capacitance,
CPROG, the following equation should be used to calculate
the maximum resistance value for RPROG:
R PROG ≤
1
2π • 100kHz • C PROG
NTC Thermistor
The battery temperature is measured by placing a negative temperature coefficient (NTC) thermistor close to the
battery pack. To use this feature connect the NTC thermistor, RNTC, between the NTC pin and ground and a bias
resistor, RNOM, from VBUS to NTC, as shown in Figure 1.
RNOM should be a 1% resistor with a value equal to the
value of the chosen NTC thermistor at 25°C (R25). The
LTC3554 will pause charging when the resistance of the
NTC thermistor drops to 0.54 times the value of R25
or approximately 54k (for a Vishay curve 1 thermistor,
this corresponds to approximately 40°C). If the battery
charger is in constant-voltage mode, the safety timer also
pauses until the thermistor indicates a return to a valid
temperature. As the temperature drops, the resistance of
the NTC thermistor rises. The LTC3554 is also designed
to pause charging when the value of the NTC thermistor
increases to 3.17 times the value of R25. For a Vishay
curve 1 thermistor this resistance, 317k, corresponds to
approximately 0°C. The hot and cold comparators each
have approximately 3°C of hysteresis to prevent oscillation
about the trip point.
Alternate NTC Thermistors and Biasing
The LTC3554 provides temperature qualified charging if
a grounded thermistor and a bias resistor are connected
to NTC. By using a bias resistor whose value is equal to
the room temperature resistance of the thermistor (R25)
the upper and lower temperatures are preprogrammed
to approximately 40°C and 0°C, respectively (assuming
a Vishay curve 1 thermistor).
The upper and lower temperature thresholds can be
adjusted by either a modification of the bias resistor value
or by adding a second adjustment resistor to the circuit.
If only the bias resistor is adjusted, then either the upper
or the lower threshold can be modified but not both. The
other trip point will be determined by the characteristics
of the thermistor. Using the bias resistor in addition to an
adjustment resistor, both the upper and the lower temperature trip points can be independently programmed
with the constraint that the difference between the upper
and lower temperature thresholds cannot decrease.
Examples of each technique are given below.
3554123ff
17
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPeration
NTC thermistors have temperature characteristics which
are indicated on resistance-temperature conversion tables.
The Vishay-Dale thermistor NTHS0603N011-N1003F, used
in the following examples, has a nominal value of 100k
and follows the Vishay curve 1 resistance-temperature
characteristic.
In the explanation below, the following notation is used.
R25 = Value of the thermistor at 25°C
RNTC|COLD = Value of thermistor at the cold trip point
rCOLD = Ratio of RNTC|COLD to R25
rHOT = Ratio of RNTC|HOT to R25
RNOM = Primary thermistor bias resistor (see Figure 2)
R1 = Optional temperature range adjustment resistor (see
Figure 2)
The trip points for the LTC3554’s temperature qualification are internally programmed at 0.35 • VBUS for the hot
threshold and 0.76 • VBUS for the cold threshold.
RNTC|HOT = Value of the thermistor at the hot trip point
20
20
0.76 • VBUS
(NTC RISING)
RNOM
100k
15
15
–
TOO_COLD
NTC
+
RNTC
100k
0.76 • VBUS
(NTC RISING)
RNOM
105k
NTC BLOCK
VBUS
VBUS
TOO_COLD
NTC
+
R1
12.7k
RNTC
100k
–
0.35 • VBUS
(NTC FALLING)
–
0.35 • VBUS
(NTC FALLING)
TOO_HOT
+
TOO_HOT
+
+
0.017 • VBUS
(NTC FALLING)
+
0.017 • VBUS
(NTC FALLING)
–
NTC_ENABLE
NTC_ENABLE
–
3554 F02
–
Figure 2. NTC Thermistor Circuit with Additional Bias Resistor
3554 F01
Figure 1. Typical NTC Thermistor Circuit
18
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
Therefore, the hot trip point is set when:
R NTC|HOT
R NOM +R NTC|HOT
• VBUS = 0.35 • VBUS
and the cold trip point is set when:
R NTC|COLD
R NOM +R NTC|COLD
• V BUS = 0.76 • V BUS
Solving these equations for RNTC|COLD and RNTC|HOT
results in the following:
RNTC|HOT = 0.538 • RNOM
and
RNTC|COLD = 3.17 • RNOM
By setting RNOM equal to R25, the above equations result
in rHOT = 0.538 and rCOLD = 3.17. Referencing these ratios
to the Vishay Resistance-Temperature Curve 1 chart gives
a hot trip point of about 40°C and a cold trip point of about
0°C. The difference between the hot and cold trip points
is approximately 40°C.
By using a bias resistor, RNOM, different in value from
R25, the hot and cold trip points can be moved in either
direction. The temperature span will change somewhat due
to the nonlinear behavior of the thermistor. The following
equations can be used to easily calculate a new value for
the bias resistor:
r
R NOM = HOT • R25
0.538
r
R NOM = COLD • R25
3.17
where rHOT and rCOLD are the resistance ratios at the desired hot and cold trip points. Note that these equations
are linked. Therefore, only one of the two trip points can
be independently set, the other is determined by the default ratios designed in the IC.
Consider an example where a 60°C hot trip point is desired.
From the Vishay curve 1 R-T characteristics, rHOT is 0.2488
at 60°C. Using the above equation, RNOM should be set to
46.4k. With this value of RNOM, the cold trip point is about
16°C. Notice that the span is now 44°C rather than the
previous 40°C. This is due to the decrease in temperature
gain of the thermistor as absolute temperature increases.
The upper and lower temperature trip points can be independently programmed by using an additional bias
resistor as shown in Figure 2. The following formulas can
be used to compute the values of RNOM and R1:
R NOM =
r COLD – r HOT
2.714
• R25
R1= 0.536 • R NOM – r HOT • R25
For example, to set the trip points to 0°C and 45°C with
a Vishay curve 1 thermistor choose:
R NOM =
3.266 – 0.4368
• 100k =104.2k
2.714
the nearest 1% value is 105k
R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k
The nearest 1% value is 12.7k. The final solution is shown
in Figure 2 and results in an upper trip point of 45°C and
a lower trip point of 0°C.
3554123ff
19
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
STeP-DOWN SWITCHING REGULATOR
drops below the VOUT UVLO threshold. If driving the stepdown switching regulator input supplies from a voltage
other than VOUT, the regulators should not be operated
outside their specified operating voltage range as operation is not guaranteed beyond this range.
Introduction
The LTC3554 includes two constant-frequency currentmode 200mA step-down switching regulators, also
known as buck regulators. At light loads, each regulator
automatically enters Burst Mode operation to maintain
high efficiency.
Output Voltage Programming
Figure 3 shows the step-down switching regulator
application circuit. The output voltage for each step-down
switching regulator is programmed using a resistor divider
from the step-down switching regulator output connected
to the feedback pins (FB1 and FB2) such that:
Applications with a near-zero-current sleep or memory
keep-alive mode can command the LTC3554 switching
regulators into a standby mode that maintains output
regulation while drawing only 1.5µA quiescent current
per active regulator. Load capability drops to 5mA per
regulator in this mode.
Switching frequency and switch slew rate are pin-selectable, allowing the application circuit to dynamically trade
off efficiency and EMI performance.
R1
VOUTx = 0.8V • +1
R2
Typical values for R1 can be as high as 2.2MΩ.
(R1 + R2) can be as high as 3MΩ. The capacitor CFB
cancels the pole created by feedback resistors and
the input capacitance of the FB pin and also helps to
improve transient response for output voltages much
greater than 0.8V. A variety of capacitor sizes can be used
for CFB but a value of 10pF is recommended for most
applications. Experimentation with capacitor sizes between
2pF and 22pF may yield improved transient response.
The regulators are enabled, disabled and sequenced (except LTC3554-3) through the pushbutton interface (see
the Pushbutton Interface section for more information). It
is recommended that the step-down switching regulator
input supply (BVIN) be connected to the system supply pin
(VOUT). This is recommended because the undervoltage
lockout circuit on the VOUT pin (VOUT UVLO) disables the
step-down switching regulators when the VOUT voltage
VIN
EN
FSEL
PWM
CONTROL
MP
SWx
L
VOUTx
MN
CFB
R1
COUT
FBx
GND
0.8V
R2
3554 F03
Figure 3. Step-down Switching Regulator Application Circuit
20
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
PGOOD Operation
The PGOOD pin is an open-drain output which indicates that
all enabled step-down switching regulators have reached
their final regulation voltage. It goes high-impedance
230ms after all enabled switching regulators reach 92%
of their regulation value. The delay allows ample time
for an external processor to reset itself. PGOOD may be
used as a power-on reset to a microprocessor powered
by the step-down switching regulators. Since PGOOD is
an open-drain output, a pull-up resistor to an appropriate
power source is needed. A suggested approach is to connect the pull-up resistor to one of the step-down switching
regulator output voltages so that power is not dissipated
while the regulators are disabled.
In hard reset, the PGOOD pin is placed in high impedance
state to minimize current draw from the battery in this ultralow power state. This will cause the PGOOD pin to signal
the wrong state (high level) if it is pulled up to a supply
that is not shut down in hard reset (e.g. BAT). If PGOOD
is pulled up to one of the step-down switching regulator
outputs then the PGOOD pin will indicate the correct state
(low level) in hard reset because the switching regulator
output will be low.
Normal Operating Mode (STBY Pin Low)
In normal mode (STBY pin low), the regulators perform
as traditional constant-frequency current mode switching
regulators. Switching frequency is determined by an internal oscillator whose frequency is selectable via the FSEL
pin. An internal latch is set at the start of every oscillator
cycle, turning on the main P-channel MOSFET switch.
During each cycle, a current comparator compares the
inductor current to the output of an error amplifier. The
output of the current comparator resets the internal latch,
which causes the main P-channel MOSFET switch to turn
off and the N-channel MOSFET synchronous rectifier to turn
on. The N-channel MOSFET synchronous rectifier turns off
at the end of the clock cycle, or when the current through
the N-channel MOSFET synchronous rectifier drops to
zero, whichever happens first. Via this mechanism, the
error amplifier adjusts the peak inductor current to deliver
the required output power. All necessary compensation
is internal to the step-down switching regulator requiring
only a single ceramic output capacitor for stability.
At light load and no-load conditions, the buck automatically
switches to a power-saving hysteretic control algorithm that
operates the switches intermittently to minimize switching
losses. Known as Burst Mode operation, the buck cycles
the power switches enough times to charge the output
capacitor to a voltage slightly higher than the regulation
point. The buck then goes into a reduced quiescent current
sleep mode. In this state, power loss is minimized while the
load current is supplied by the output capacitor. Whenever
the output voltage drops below a predetermined value, the
buck wakes from sleep and cycles the switches again until
the output capacitor voltage is once again slightly above
the regulation point. Sleep time thus depends on load
current, since the load current determines the discharge
rate of the output capacitor.
Standby Mode (STBY Pin High)
There are situations where even the low quiescent current
of Burst Mode operation is not low enough. For instance,
in a static memory keep alive situation, load current may
fall well below 1µA. In this case, the 25µA typical BVIN
quiescent current per active regulator in Burst Mode operation becomes the main factor determining battery run time.
Standby mode cuts BVIN quiescent current down to just
1.5µA per active regulator, greatly extending battery run
time in this essentially no-load region of operation. The
application circuit commands the LTC3554 into and out
of standby mode via the STBY pin logic input. Bringing
the STBY pin high places both regulators into standby
mode, while bringing it low returns them to Burst Mode
operation. In standby mode, load capability drops to 5mA
per regulator.
3554123ff
21
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
In standby mode, each regulator operates hysteretically.
When the FB pin voltage falls below the internal 0.8V
reference, a current source from BVIN to SW turns on,
delivering current through the inductor to the switching
regulator output capacitor and load. When the FB pin
voltage rises above the reference plus a small hysteresis
voltage, that current is shut off. In this way, output regulation is maintained.
Since the power transfer from BVIN to SW is through a
high impedance current source rather than through a low
impedance MOSFET switch, power loss scales with load
current as in a linear low dropout (LDO) regulator, rather
than as in a switching regulator. For near-zero load conditions where regulator quiescent current is the dominant
power loss, standby mode is ideal. But at any appreciable
load current, Burst Mode operation yields the best overall
conversion efficiency.
Shutdown
Each step-down switching regulator is shut down and
enabled via the pushbutton interface. In shutdown, each
switching regulator draws only a few nanoamps of leakage current from the BVIN pin. Each disabled regulator
also pulls down on its output with a 10k resistor from its
switch pin to ground.
Dropout Operation
It is possible for a step-down switching regulator’s input
voltage to fall near or below its programmed output voltage (e.g., a battery voltage of 3.4V with a programmed
output voltage of 3.3V). When this happens, the PMOS
switch duty cycle increases to 100%, keeping the switch on
22
continuously. Known as dropout operation, the respective
output voltage equals the regulator’s input voltage minus
the voltage drops across the internal P-channel MOSFET
and the inductor.
Soft-Start Operation
In normal operating mode, soft-start works by gradually
increasing the peak inductor current for each step-down
switching regulator over a 500μs period. This allows each
output to rise slowly, helping minimize the inrush current
needed to charge up the output capacitor. A soft-start cycle
occurs whenever a given switching regulator is enabled.
Soft-start occurs only in normal operation, but not in
standby mode. Standby mode operation is already inherently current-limited, since the regulator works by intermittently turning on a current source from BVIN to SW.
Changing the state of the STBY pin while the regulators
are operating doesn’t trigger a new soft-start cycle, to
avoid glitching the outputs.
Frequency/Slew Rate Select
The FSEL pin allows an application to dynamically trade off
between highest efficiency and reduced electromagnetic
interference (EMI) emission.
When FSEL is high, the switching regulator frequency is
set to 2.25MHz to stay out of the AM radio band. Also,
new patented circuitry is enabled which limits the slew rate
of the switch nodes (SW1 and SW2). This new circuitry
is designed to transition the switch node over a period of
a few nanoseconds, significantly reducing radiated EMI
and conducted supply noise.
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
When FSEL is low, the frequency of the switching regulators
is reduced to 1.125Mhz. The slower switching frequency
reduces switching losses and raises efficiency as shown
in Figures 4 and 5. Switch node slew rate is also increased
to minimize transition losses. As the programmed output
voltage decreases, the difference in efficiency is more
appreciable.
switching regulators from operating at low supply voltages
where loss of regulation or other undesirable operation
may occur. If driving the step-down switching regulator
input supply from a voltage other than the VOUT pin, the
regulators should not be operated outside the specified
operating range as operation is not guaranteed beyond
this range.
Low Supply Operation
Inductor Selection
An undervoltage lockout circuit on the VOUT pin (VOUT
UVLO) shuts down the step-down switching regulators
when VOUT drops below about 2.6V. It is thus recommended that the step-down switching regulator input
supply (BVIN) be connected directly to the power path
output (VOUT). The UVLO prevents the step-down
Many different sizes and shapes of inductors are available from numerous manufacturers. Choosing the right
inductor from such a large selection of devices can be
overwhelming, but following a few basic guidelines will
make the selection process much simpler.
90
90
100
EFFICIENCY
60
10
50
POWER LOSS
40
1
30
0.1
20
FSEL = L
FSEL = H
10
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
0
1000
3554 F04
Figure 4. 1.2V Output Efficiency and Power Loss vs
Load Current
100
EFFICIENCY
70
60
10
50
POWER LOSS
40
1
30
0.1
20
FSEL = L
FSEL = H
10
0
0.01
POWER LOSS (mW)
70
1000
BAT = 3.8V
80
POWER LOSS (mW)
EFFICIENCY (%)
80
100
1000
BAT = 3.8V
EFFICIENCY (%)
100
0.1
1
10
100
LOAD CURRENT (mA)
0
1000
3554 F05
Figure 5. 3.3V Output Efficiency and Power Loss
vs Load Current
3554123ff
23
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
Inductor value should be chosen based on the desired
output voltage. See Table 2. Table 3 shows several inductors
that work well with the step-down switching regulators.
These inductors offer a good compromise in current rating, DCR and physical size. Consult each manufacturer for
detailed information on their entire selection of inductors.
Choose an inductor with a DC current rating at least 1.5
times larger than the maximum load current to ensure that
the inductor does not saturate during normal operation.
If output short circuit is a possible condition, the inductor should be rated to handle the maximum peak current
specified for the step-down converters.
Larger value inductors reduce ripple current, which improves output ripple voltage. Lower value inductors result in
higher ripple current and improved transient response time,
but will reduce the available output current. To maximize
efficiency, choose an inductor with a low DC resistance.
Different core materials and shapes will change the size/
current and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials are
small and do not radiate much energy, but generally cost
more than powdered iron core inductors with similar
Table 1. Ceramic Capacitor Manufacturers
Table 2. Choosing the Inductor Value
AVX
www.avxcorp.com
DESIRED OUTPUT VOLTAGE
RECOMMENDED INDUCTOR VALUE
Murata
www.murata.com
1.8V or Less
10µH
Taiyo Yuden
www.t-yuden.com
1.8V to 2.5V
6.8µH
Vishay Siliconix
www.vishay.com
2.5V to 3.3V
4.7µH
TDK
www.tdk.com
Table 3. Recommended Inductors for Step-Down Switching Regulators
INDUCTOR PART NO.
SIZE (L × W × H) (mm)
L (µH)
MAX IDC (A)
MAX DCR (Ω)
1117AS-4R7M
1117AS-6R8M
1117AS-100M
4.7
6.8
10
0.64
0.54
0.45
0.18*
0.250*
0.380*
3.0 × 2.8 × 1.0
Toko
www.toko.com
MANUFACTURER
CDRH2D11BNP-4R7N
CDRH2D11BNP-6R8N
CDRH2D11BNP-100N
4.7
6.8
10
0.7
0.6
0.48
0.248
0.284
0.428
3.0 × 3.0 × 1.2
Sumida
www.sumida.com
SD3112-4R7-R
SD3112-6R8-R
SD3112-100-R
4.7
6.8
10
0.8
0.68
0.55
0.246*
0.291*
0.446*
3.1 × 3.1 × 1.2
Cooper
www.cooperet.com
EPL2014-472ML_
EPL2014-682ML_
EPL2014-103ML_
4.7
6.8
10
0.88
0.8
0.6
0.254
0.316
0.416
2.0 × 1.8 × 1.4
Coilcraft
www.coilcraft.com
* = Typical DCR
24
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
electrical characteristics. Inductors that are very thin or
have a very small volume typically have much higher core
and DCR losses, and will not give the best efficiency. The
choice of which style inductor to use often depends more
on the price versus size, performance and any radiated
EMI requirements than on what the step-down switching
regulators requires to operate.
PUSHBUTTON INTERFACE
The inductor value also has an effect on Burst Mode
operation. Lower inductor values will cause Burst Mode
switching frequency to increase.
PUP2
State Diagram/Operation
Figure 6 shows the LTC3554 pushbutton state diagram.
HR
EXTPWR OR
PB400MS
EXTPWR OR
PB400MS
5SEC
Input/Output Capacitor Selection
Low ESR (equivalent series resistance) ceramic capacitors
should be used at both step-down switching regulator
outputs as well as at the step-down switching regulator
input supply. Only X5R or X7R ceramic capacitors should
be used because they retain their capacitance over wider
voltage and temperature ranges than other ceramic types.
For good transient response and stability the output capacitor for each step-down switching regulator should retain
at least 4μF of capacitance over operating temperature and
bias voltage. Generally, a good starting point is to use a
10μF output capacitor.
The switching regulator input supply should be bypassed
with a 2.2μF capacitor. Consult with capacitor manufacturers for detailed information on their selection and
specifications of ceramic capacitors. Many manufacturers
now offer very thin ( VUVLO and VBUS – VBAT > VDUVLO),
the pushbutton circuity immediately enters the PUP1 state.
For this to work reliably, the BAT pin voltage must be kept
well-behaved when no battery is connected. Ensure this
by bypassing the BAT pin to GND with an RC network consisting of a 100µF ceramic capacitor in series with 0.3Ω.
1
BAT
0
1
VBUS
0
1
ON (PB)
0
1
PBSTAT
0
1
100ms
BUCK1
0
1
BUCK2*
0
1
PGOOD
0
1
230ms
5s
PWR_ON1
0
1
PWR_ON2
STATE
5s
0
POFF/HR
PUP2/PUP1
*BUCK1 AND BUCK2 FOR THE LTC3554-3
PON
3554 TD02
Figure 8. Power-Up Via Applying External Power
28
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
Power-Up Via Asserting PWR_ON Pins
Power-Down Via PWR_ON De-Assertion
Figure 9 shows the LTC3554 powering up by driving
PWR_ON1 high. For this example the pushbutton circuitry
starts in the POFF or HR state with a battery connected
and all bucks disabled. Once PWR_ON1 goes high, the
pushbutton circuitry enters the PON state and buck1
powers up. Once buck1’s output is within 8% of its regulation voltage for 230ms, PGOOD is asserted. Similarly,
if PWR_ON2 is brought high at a later time, buck2 will
power up. The pushbutton circuitry remains in the PON
state. During the time that buck2 powers up, PGOOD will
be held low. PGOOD will be asserted again once buck2 is
within 8% of its regulation for 230ms.
Figure 10 shows the LTC3554 powering down by μC/μP
control. For this example the pushbutton circuitry starts
in the PON state with a battery connected and all bucks
enabled. The user presses the pushbutton (ON low) for at
least 50ms, which generates a debounced, low impedance
pulse on the PBSTAT output. After receiving the PBSTAT
signal, the μC/μP software decides to drive the PWR_ON
inputs low in order to power down. After the last PWR_ON
pin goes low, the pushbutton circuitry will enter the PDN2
state. In the PDN2 state a one second wait time is initiated after which the pushbutton circuitry enters the POFF
state. During this one second time, the ON and PWR_ON
inputs as well as external power application are ignored
to allow all LTC3554 generated supplies to go low. Though
the above assumes a battery present, the same operation
would take place with a valid external supply (VBUS) with
or without a battery present.
Powering up via PWR_ON is useful for applications
containing an always-on μC that’s not powered by the
LTC3554 regulators. That μC can power the application
up and down for housekeeping and other activities not
needing the user’s control.
1
1
BAT
BAT
0
1
1
VBUS
VBUS
0
ON (PB)
ON (PB)
0
1s
0
50ms
1
1
PBSTAT
0
0
µC/µP CONTROL
1
1
PWR_ON1
PWR_ON1
0
0
µC/µP CONTROL
1
1
PWR_ON2
PWR_ON2
0
0
1
1
BUCK1
BUCK1
0
0
1
1
BUCK2
BUCK2
0
0
230ms
1
230ms
1
PGOOD
PGOOD
0
0
STATE
0
1
1
PBSTAT
0
POFF/HR
STATE
PON
3554 TD03
Figure 9. Power-Up Via Asserting PWR_ON Pins
PON
PDN2
POFF
3554 TD04
Figure 10. Power-Down Via PWR_ON De-Assertion
3554123ff
29
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
Holding ON low through the one second power-down
period will not cause a power-up event at end of the one
second period. The ON pin must be brought high following
the power-down event and then go low again to establish
a valid power-up event.
UVLO Minimum Off-Time Timing (Low Battery)
Figure 11 assumes the battery is either missing or at a
voltage below the VOUT UVLO threshold, and the application is running via external power (VBUS). A glitch on the
external supply causes VOUT to drop below the VOUT UVLO
threshold temporarily. This VOUT UVLO condition causes
the pushbutton circuitry to transition from the PON state
to the PDN2 state. Upon entering the PDN2 state PGOOD
will go low and the bucks power down together.
1
BAT
0
1
VBUS
0
1
ON (PB)
0
0
5s
1
PWR_ON1
0
5s
1
PWR_ON2
0
Hard Reset Timing
1s, BUCK1 POWERS UP
1
BUCK1
0
BUCK2 POWERS UP
1
BUCK2
0
230ms
1
PGOOD
0
STATE
PON
PDN2
PUP2
PON
3554 TD05
Figure 11. UVLO Minimum Off-Time Timing
30
Not depicted here, but in the case where the PWR_ON
pins are driven by a supply other than the bucks, and are
able to remain high while both bucks are off in the PDN2
state, then as per the state diagram in Figure 6, once the
one second PDN2 delay is over, the pushbutton circuitry
enters the POFF state. Provided at least one PWR_ON pin
is high, and VOUT is no longer in UVLO, the pushbutton
circuitry will transition directly into the PON state, enabling
the buck(s) corresponding to the asserted PWR_ON pin(s).
Note: If VOUT drops too low (below about 1.9V ) the
LTC3554 will see this as a POR condition and will enter
the PDN1 rather than the PDN2 state. One second later the
part will transition to the HR state. Under these conditions
an explicit power up event (such as a pushbutton press)
may be required to bring the LTC3554 out of hard reset.
1
PBSTAT
In the typical case where the PWR_ON1 and PWR_ON2 pins
are driven by logic powered by the bucks, the PWR_ON1
and PWR_ON2 pins would also go low, as depicted in
Figure 11. If the external supply recovers after entering the
PDN2 state such that VOUT is no longer in UVLO, then the
LTC3554 will transition back into the PUP2 state once the
PDN2 one second delay is complete. Following the state
diagram, the transition from PDN2 to PUP2 in this case
actually occurs via a brief visit to the POFF state, during
which the state machine immediately recognizes that valid
external power is available and transitions into the PUP2
state. Entering the PUP2 state will cause the bucks to
power up as described previously in the power-up sections.
HARD RESET provides an ultralow power-down state for
shipping or long term storage as well as a way to power
down the application in case of a software lockup. In the
case of software lockup, the user can hold the pushbutton (ON low) for 5 seconds for LTC3554/LTC3554-1
(14 seconds for LTC3554-2/LTC3554-3) and a hard reset
event (HRST) will occur, placing the pushbutton circuitry
in the power-down (PDN1) state. At this point the bucks
will be shut down and PGOOD will go low. Following a one
second power-down period the pushbutton circuitry will
enter the hard reset state (HR).
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
Holding ON low through the one second power-down
period will not cause a power-up event at end of the one
second period. ON must be brought high following the
power-down event and then go low again for 400ms to
establish a valid power-up event, as shown in Figure 12.
1
BAT
0
1
VBUS
VOUT1
1V/DIV
0
tON_HR
1
ON (PB)
0
0V
VOUT2
0.5V/DIV
50ms
1
PBSTAT
The regulators in Figure 13 are slewing up with nominal
output capacitors and no-load. Adding a load or increasing
output capacitance on any of the outputs will reduce the
slew rate and lengthen the time it takes the regulator to
get into regulation. In the LTC3554-3, buck1 and buck2
power up at the same time without sequencing.
0V
0
400ms
100µs/DIV
3554 F13
Figure 13. Power-Up Sequencing
1
BUCK1
0
LAYOUT AND THERMAL CONSIDERATIONS
1
BUCK2
0
PWR_ON1
Printed Circuit Board Power Dissipation
1s
1
0
1
PWR_ON2
0
1
PGOOD
0
STATE
PON
PDN1
HR
PUP1
3554 TD06
Figure 12. Hard Reset Via Holding ON Low
Power-Up Sequencing (Except LTC3554-3)
Figure 13 shows the actual power-up sequencing of the
LTC3554. Buck1 and buck2 are both initially disabled (0V).
Once the pushbutton has been applied (ON low) for 400ms
buck1 is enabled. Buck1 slews up and enters regulation.
The actual slew rate is controlled by the soft start function
of buck1 in conjunction with output capacitance and load
(see the Step-Down Switching Regulator Operation section for more information). When buck1 is within about
8% of final regulation, buck2 is enabled and slews up
into regulation. 230ms after buck2 is within 8% of final
regulation, the PGOOD output will go high impedance.
In order to be able to deliver maximum charge current
under all conditions, it is critical that the Exposed Pad
on the backside of the LTC3554 package is soldered to
a ground plane on the board. Correctly soldered to a
2500mm2 ground plane on a double-sided 1oz copper
board, the LTC3554 has a thermal resistance (qJA) of approximately 70°C/W. Failure to make good thermal contact
between the Exposed Pad on the backside of the package
and an adequately sized ground plane will result in thermal
resistances far greater than 70°C/W.
The conditions that cause the LTC3554 to reduce charge
current due to the thermal protection feedback can be
approximated by considering the power dissipated in the
part. For high charge currents the LTC3554 power dissipation is approximately:
PD = (VBUS–BAT) • IBAT + PD(REGS)
where PD is the total power dissipated, VBUS is the supply
voltage, BAT is the battery voltage, and IBAT is the battery
charge current. PD(REGS) is the sum of power dissipated
on chip by the step-down switching regulators.
3554123ff
31
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
The power dissipated by a step-down switching regulator
can be estimated as follows:
PD(SWx) = (BOUTx • IOUT) • (100 - Eff)/100
Where BOUTx is the programmed output voltage, IOUT
is the load current and Eff is the % efficiency which can
be measured or looked up on an efficiency table for the
programmed output voltage.
Thus the power dissipated by all regulators is:
PD(REGS) = PD(SW1) + PD(SW2)
It is not necessary to perform any worst-case power dissipation scenarios because the LTC3554 will automatically
reduce the charge current to maintain the die temperature
at approximately 110°C. However, the approximate ambient temperature at which the thermal feedback begins to
protect the IC is:
TA = 110°C – PD • qJA
Example: Consider the LTC3554 operating from a wall
adapter with 5V (VBUS) providing 400mA (IBAT) to charge a
Li-Ion battery at 3.3V (BAT). Also assume PD(REGS) = 0.3W,
so the total power dissipation is:
PD = (5V – 3.3V) • 400mA + 0.3W = 0.98W
The ambient temperature above which the LTC3554 will begin to reduce the 400mA charge current, is approximately:
TA = 110°C – 0.98W • 70°C/W = 41.4°C
The LTC3554 can be used above 41.4°C, but the charge
current will be reduced below 400mA. The charge current
at a given ambient temperature can be approximated by:
PD = (110°C – TA) / θJA = (VBUS – BAT) • IBAT + PD(REGS)
Thus:
IBAT = [(110°C – TA) / qJA - PD(REGS)]
(VBUS – BAT)
Consider the above example with an ambient temperature of 60°C. The charge current will be reduced to
approximately:
Printed Circuit Board Layout
When laying out the printed circuit board, the following
list should be followed to ensure proper operation of the
LTC3554:
1. The Exposed Pad of the package (Pin 21) should connect
directly to a large ground plane to minimize thermal
and electrical impedance.
2. The trace to the step-down switching regulator input
supply pin (BVIN) and its decoupling capacitor should be
kept as short as possible. The GND side of this capacitor
should connect directly to the ground plane of the part.
This capacitor provides the AC current to the internal
power MOSFETs and their drivers. It is important to
minimize inductance from this capacitor to the pin of
the LTC3554. Connect BVIN to VOUT through a short
low impedance trace.
3. The switching power traces connecting SW1 and SW2
to their respective inductors should be minimized to
reduce radiated EMI and parasitic coupling. Due to the
large voltage swing of the switching nodes, sensitive
nodes such as the feedback nodes (FB1 and FB2) should
be kept far away or shielded from the switching nodes
or poor performance could result.
4. Connections between the step-down switching regulator inductors and their respective output capacitors
should be kept as short as possible. The GND side of
the output capacitors should connect directly to the
thermal ground plane of the part.
5. Keep the buck feedback pin traces (FB1 and FB2) as
short as possible. Minimize any parasitic capacitance
between the feedback traces and any switching node
(i.e., SW1, SW2 and logic signals). If necessary, shield
the feedback nodes with a GND trace.
6. Connections between the LTC3554 PowerPath pins
(VBUS and VOUT) and their respective decoupling capacitors should be kept as short as possible. The GND
side of these capacitors should connect directly to the
ground plane of the part.
IBAT = [(110°C - 60°C) / 70°C/W - 0.3W]/(5V – 3.3V)
IBAT = (0.71W - 0.3W) / 1.7V = 241mA
32
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Typical Application
U1
20
4.35V TO 5.5V
USB INPUT
15
VBUS
VOUT
NTC
CHRG
LTC3554
16
RPROG
1.87k
1
19
9
2
10
4
8
3
5
PB1
PROG
BAT
BVIN
HPWR
SW1
FB1
FSEL
17
SW2
PWR_ON2
PBSTAT
ON
GND
FB2
+
3 CELL
ALKALINE
OR LITHIUM
12
C2
2.2µF
13
6
STBY
PGOOD
C1
10µF
14
SUSP
PWR_ON1
SYSTEM LOAD
18
11
7
U2
L1 10µH
C3
10pF
L2
10µH
C5
10pF
2.5V
RUP1
1M
I/O
C4
10µF
RLO1
464k
1.8V
RUP2
590k
C6
10µF
CORE
µC
RLO2
464k
R4
100k
R2
100k
R3
100k
PBSTAT
PGOOD
STBY
FSEL
EN
SUSP
HPWR
3554 F14
Figure 14. 3-Cell Alkaline/Lithium with PowerPath (Charger Disabled)
3554123ff
33
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
UD Package
UD Package
20-Lead Plastic QFN (3mm × 3mm)
20-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1720 Rev A)
(Reference LTC DWG # 05-08-1720 Rev A)
0.70 ±0.05
3.50 ± 0.05
(4 SIDES)
1.65 ± 0.05
2.10 ± 0.05
PACKAGE
OUTLINE
0.20 ±0.05
0.40 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
3.00 ± 0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
0.75 ± 0.05
R = 0.05
TYP
PIN 1
TOP MARK
(NOTE 6)
PIN 1 NOTCH
R = 0.20 TYP
OR 0.25 × 45°
CHAMFER
R = 0.115
TYP
19 20
0.40 ± 0.10
1
2
1.65 ± 0.10
(4-SIDES)
(UD20) QFN 0306 REV A
0.200 REF
0.00 – 0.05
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
34
0.20 ± 0.05
0.40 BSC
3554123ff
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Revision History
REV
DATE
DESCRIPTION
A
7/10
PD package information removed and UD package information added to data sheet
B
01/11
PAGE NUMBER
1 to 16
Update to Typical Application
1
LTC3554EUD added and LTC3554EPD designated Obsolete in Order Information section
2
Note 2 updated
5
Pin 21 description updated
12
Updated Related Parts
36
LTC3554-2 Option Added. Reflected throughout the data sheet
1 to 36
1 to 36
C
10/11
LTC3554-1 Option Added. Reflected throughout the data sheet
D
01/12
Corrected title on axis of graph G23
10
Updated Block Diagram
13
Added text to State Diagram/Operation section
25
E
F
08/12
04/15
Added new part number LTC3554-3
Throughout
Added Options table
2
Changed θJA of package from 70°C/W to 58.7°C/W
2
3554123ff
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
35
LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
Typical Application
4.35V TO 5.5V
USB INPUT
20
C7
10µF
15
R1
100k
R2
100k
VBUS
VOUT
NTC
CHRG
16
RPROG
1.87k
1
19
9
2
10
4
8
3
5
PB1
PROG
BAT
HPWR
BVIN
SW1
FSEL
FB1
R3
17
+
SW2
PWR_ON2
PBSTAT
ON
GND
FB2
Li-Ion
BATTERY
12
C2
2.2µF
13
L1 4.7µH
C3
10pF
6
STBY
PGOOD
EN
14
SUSP
PWR_ON1
1.8V
C1
10µF
LTC3554
T
LDO
SYSTEM LOAD
18
11
L2
10µH
7
C5
10pF
3.3V
RUP1
2.05M
MEMORY
I/O
C4
10µF
RLO1
649k
1.2V
RUP2
332k
C6
10µF
CORE
µC
RLO2
649k
R2
100k
R3
100k
PBSTAT
PWR_ON2
PGOOD
STBY
FSEL
PWR_ON1
SUSP
HPWR
3554 F15
Figure 15. USB PowerPath with LI-Ion Battery (NTC Qualified Charging)
Related Parts
PART NUMBER DESCRIPTION
COMMENTS
LTC3455
Dual DC/DC Converter with USB Power
Manager and Li-Ion Battery Charger
Seamless Transition Between Input Power Sources: Li-Ion Battery, USB and 5V Wall
Adapter, 4mm × 4mm QFN-24 Package
LTC3456
2-Cell, Multioutput DC/DC Converter with
USB Power Manager
Seamless Transition Between 2-Cell Battery, USB and AC Wall Adapter Input Power Sources,
4mm × 4mm QFN-24 Package
LTC3557
USB Power Manager with Li-Ion Charger,
Triple Step-Down DC/DC Regulators
Triple Step-Down Switching Regulators (600mA, 400mA); 4mm × 4mm QFN Package
LTC3559
USB Charger with Dual Buck Regulators
Adjustable, Synchronous Buck Converters, 3mm × 3mm QFN-16 Package
LTC4080
500mA Standalone Charger with 300mA
Synchronous Buck
Charges Single-Cell Li-Ion Batteries, Timer Termination + C/10, Thermal Regulation, Buck
Output: 0.8V to VBAT, Buck Input VIN: 2.7V to 5.5V, 3mm × 3mm DFN-10 Package
LTC3553
µPower PMIC/Charger/Buck/LDO
3mm × 3mm × 0.75mm QFN-20 Package
36 Linear Technology Corporation
3554123ff
LT 0415 REV F • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2009
工商网监
湘ICP备2023018690号
