LTC3622/
LTC3622-2/LTC3622-23/5
17V, Dual 1A
Synchronous Step-Down Regulator
with Ultralow Quiescent Current
DESCRIPTION
FEATURES
Dual Step-Down Outputs: 1A Per Channel
nn Wide V Range: 2.7V to 17V
IN
nn Wide V
OUT Range: 0.6V to VIN
nn Up to 95% Efficiency
nn No-Load I = 5µA with Both Channels Enabled;
Q
IQ < 4µA with Only One Channel Enabled
nn High Efficiency, Low Dropout Operation
(100% Duty Cycle)
nn Constant Frequency (1MHz/2.25MHz) with External
Frequency Synchronization
nn ±1% Output Voltage Accuracy
nn Current Mode Operation for Excellent Line and Load
Transient Response
nn Phase Shift Programmable with External Clock
nn Selectable Current Limit
nn Internal Compensation and Soft-Start
nn Compact 14-Pin DFN (3mm × 4mm) and 16-Lead
MSOP Packages
nn
The LTC®3622 is a dual 1A output, high efficiency synchronous monolithic step-down regulator capable of operating
from input supplies up to 17V. The switching frequency is
fixed to 1MHz or 2.25MHz with a ±50% synchronization
range to an external clock. The regulator features ultralow
quiescent current and high efficiency over a wide output
voltage range.
The step-down regulators operate from an input voltage
range of 2.7V to 17V and provide an adjustable output
from 0.6V to VIN while delivering up to 1A of output current. A user-selectable mode input is provided to allow
the user to trade off ripple noise for light load efficiency.
Burst Mode® operation provides the highest efficiency at
light loads, while pulse-skipping mode provides the lowest
ripple noise. The switching regulators can be synchronized
to an external clock. Furthermore, fixed VOUT options are
available to eliminate the external feedback resistors.
List of LTC3622 Options
APPLICATIONS
PART NAME
FREQUENCY
VOUT
Battery Powered Systems
nn Point-of-Load Supplies
nn Portable – Handheld Scanners
LTC3622
1.00MHz
Adjustable
LTC3622-2
2.25MHz
Adjustable
LTC3622-23/5
2.25MHZ
5V/3.3V
nn
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents, including 5481178, 6580258, 6498466, 6611131, 5705919.
TYPICAL APPLICATION
Efficiency vs Load Current
2.5V/5V VOUT Application, fSW = 1MHz
VIN1
INTVCC
VIN2
C1
1µF
RUN1
RUN2
PHASE
ILIM
LTC3622
VOUT1
2.5V
1A
4.7µH
6.8µH
SW1
COUT1
22µF
22pF
SW2
619k
619k
FB2
FB1
196k
GND
84.5k
22pF
VOUT2
5V
1A
COUT2
22µF
3622 TA01
Document Feedback
0.5
80
MODE/SYNC
For more information www.analog.com
70
0.4
60
50
0.3
40
20
10
0.2
VOUT1 = 2.5V
VOUT2 = 5V
30
VIN = 12V
fSW = 1MHz
Burst Mode OPERATION
0
0.0001
0.001
0.01
0.1
LOAD CURRENT (A)
POWER LOSS (W)
CIN
10µF
0.6
90
EFFICIENCY (%)
VIN
5.5V TO 17V
100
0.1
1
3622 TA01b
0
Rev D
1
LTC3622/
LTC3622-2/LTC3622-23/5
TABLE OF CONTENTS
Features............................................................................................................................. 1
Applications........................................................................................................................ 1
Typical Application ................................................................................................................ 1
Description......................................................................................................................... 1
Absolute Maximum Ratings...................................................................................................... 3
Pin Configuration.................................................................................................................. 3
Order Information.................................................................................................................. 3
Electrical Characteristics......................................................................................................... 4
Typical Performance Characteristics........................................................................................... 6
Pin Functions....................................................................................................................... 9
Block Diagram.....................................................................................................................10
Operation..........................................................................................................................11
Applications Information........................................................................................................13
Typical Applications..............................................................................................................20
Package Description.............................................................................................................21
Revision History..................................................................................................................23
Typical Application...............................................................................................................24
Related Parts......................................................................................................................24
Rev D
2
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN1, VIN2, SVIN (MSOP Only) (Note 2)........ –0.3V to 17V
RUN1, RUN2...............................................–0.3V to VIN1
MODE/SYNC, FB1, FB2................................. –0.3V to 6V
PGOOD1, PGOOD2, ILIM, PHASE................... –0.3V to 6V
Operating Junction Temperature Range (Note 3)
LTC3622E........................................... –40°C to 125°C
LTC3622I............................................ –40°C to 125°C
LTC3622H........................................... –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
PIN CONFIGURATION
TOP VIEW
VIN1
1
14 SW1
PGOOD1
2
13 RUN1
MODE/SYNC
3
PHASE
4
PGOOD2
5
10 FB2
ILIM
6
9 RUN2
VIN2
7
8 SW2
15
GND
TOP VIEW
VIN1
SVIN
PGOOD1
MODE/SYNC
PHASE
PGOOD2
ILIM
VIN2
12 FB1
11 INTVCC
1
2
3
4
5
6
7
8
17
GND
16
15
14
13
12
11
10
9
SW1
NC
RUN1
FB1
INTVCC
FB2
RUN2
SW2
MSE PACKAGE
16-LEAD PLASTIC MSE
DE PACKAGE
14-LEAD (4mm × 3mm) PLASTIC DFN
TJMAX = 150°C, θJA = 40°C/W, θJC = 4.4°C/W
EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB
TJMAX = 150°C, θJA = 40°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3622EDE#PBF
LTC3622EDE#TRPBF
3622
14-Lead (3mm x 4mm) Plastic DFN
–40°C to 125°C
LTC3622IDE#PBF
LTC3622IDE#TRPBF
3622
14-Lead (3mm x 4mm) Plastic DFN
–40°C to 125°C
LTC3622HDE#PBF
LTC3622HDE#TRPBF
3622
14-Lead (3mm x 4mm) Plastic DFN
–40°C to 150°C
LTC3622EMSE#PBF
LTC3622EMSE#TRPBF
3622
16-Lead Plastic MSOP
–40°C to 125°C
LTC3622IMSE#PBF
LTC3622IMSE#TRPBF
3622
16-Lead Plastic MSOP
–40°C to 125°C
LTC3622HMSE#PBF
LTC3622HMSE#TRPBF
3622
16-Lead Plastic MSOP
–40°C to 150°C
LTC3622EDE-2#PBF
LTC3622EDE-2#TRPBF
36222
14-Lead (3mm x 4mm) Plastic DFN
–40°C to 125°C
LTC3622IDE-2#PBF
LTC3622IDE-2#TRPBF
36222
14-Lead (3mm x 4mm) Plastic DFN
–40°C to 125°C
LTC3622HDE-2#PBF
LTC3622HDE-2#TRPBF
36222
14-Lead (3mm x 4mm) Plastic DFN
–40°C to 150°C
LTC3622EMSE-2#PBF
LTC3622EMSE-2#TRPBF
36222
16-Lead Plastic MSOP
–40°C to 125°C
LTC3622IMSE-2#PBF
LTC3622IMSE-2#TRPBF
36222
16-Lead Plastic MSOP
–40°C to 125°C
LTC3622HMSE-2#PBF
LTC3622HMSE-2#TRPBF
36222
16-Lead Plastic MSOP
–40°C to 150°C
LTC3622EDE-23/5#PBF
LTC3622EDE-23/5#TRPBF
223/5
14-Lead (3mm x 4mm) Plastic DFN
–40°C to 125°C
LTC3622IDE-23/5#PBF
LTC3622IDE-23/5#TRPBF
223/5
14-Lead (3mm x 4mm) Plastic DFN
–40°C to 125°C
LTC3622HDE-23/5#PBF
LTC3622HDE-23/5#TRPBF
223/5
14-Lead (3mm x 4mm) Plastic DFN
–40°C to 150°C
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
Rev D
For more information www.analog.com
3
LTC3622/
LTC3622-2/LTC3622-23/5
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN1 = VIN2 = 12V, unless otherwise noted. (Notes 3, 6)
SYMBOL PARAMETER
CONDITIONS
MIN
2.7
17
V
MSOP Package
2.7
17
V
VIN1, VIN2 Operating Voltage
SVIN Operating Voltage
VOUT Operating Voltage
IQ
VFB
Input Quiescent Current
Regulated Feedback Voltage
TYP
0.6
Active Mode, VRUN1 = VRUN2 = 2V (Note 4)
Burst Mode Operation, VRUN1 = VRUN2 = 2V,
MODE/SYNC = 3V, No Load
Shutdown Mode; VRUN1 = VRUN2 = 0V
LTC3622/LTC3622-2
MAX
UNITS
VIN
V
3
5
10
mA
µA
0.1
±1
µA
0.594
0.591
0.6
0.6
0.606
0.609
V
l
10
nA
l
4.950
4.925
5.0
5.0
5.050
5.075
V
V
l
3.267
3.250
3.3
3.3
3.333
3.350
V
V
IFB
FB Input Current
LTC3622/LTC3622-2
VOUT1
Regulated Fixed Output Voltage
(Channel 1)
LTC3622-23/5
Regulated Fixed Output Voltage
(Channel 2)
LTC3622-23/5
Feedback Input Leakage Current
LTC3622-23/5
1
5
µA
Reference Voltage Line Regulation
VIN = 2.7V to 17V (Note 5)
0.01
0.015
%/V
Output Voltage Load Regulation
(Note 5)
0.1
1
1
µA
µA
VOUT2
IFB(VOUT)
0.1
0.1
NMOS Switch Leakage
PMOS Switch Leakage
RDS(ON)
NMOS On-Resistance
PMOS On-Resistance
Maximum Duty Cycle
VFB = 0V
tON(MIN)
Minimum On-Time
VFB = 0.7V, VIN1 = VIN2 = 5
VRUN
RUN Input High
RUN Input Low
RUN Input Current
VMODE
VIN = 5V
%
0.15
0.37
l
100
%
75
ns
0.35
VRUN = 12V
0.1
Pulse-Skipping Mode
Burst Mode Operation
VINTVCC–0.4
PHASE Input Threshold
Input Low
Input High
2.0
ILIM Input Threshold
Input Low
Input High
VINTVCC–0.1
Ω
Ω
1.0
V
V
±20
nA
0.15
V
V
0.4
V
V
0.1
INTVCC
V
V
tSS
Soft Start Time
0.5
ILIM
Peak Current Limit
VIN > 5V
VILIM = 0.1V (Both Channels)
VILIM = INTVCC – 0.1V (Both Channels)
VILIM = Floating, Channel 1
VILIM = Floating, Channel 2
1.6
0.8
1.6
0.8
1.8
1.0
1.8
1.0
2.0
1.2
2.0
1.2
VINTVCC Undervoltage Lockout
VIN Ramping Up
2.3
2.5
2.65
VINTVCC Undervoltage Lockout Hysteresis
ms
160
VIN Overvoltage Lockout Rising
l
VIN Overvoltage Lockout Hysteresis
18
19
300
A
A
A
A
V
mV
20
V
mV
Rev D
4
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN1 = VIN2 = 12V, unless otherwise noted. (Notes 3, 6)
SYMBOL PARAMETER
fOSC
Oscillator Frequency
CONDITIONS
LTC3622-2/LTC3622-23/5 –40°C ≤ TA ≤ 150°C
LTC3622
–40°C ≤ TA ≤ 125°C
LTC3622
–40°C ≤ TA ≤ 150°C
External CLK Amplitude
SYNC Capture Range
VINTVCC
l
l
l
MIN
TYP
MAX
UNITS
1.8
0.82
0.75
2.25
1.00
1.00
2.6
1.16
1.16
MHz
MHz
MHz
0.4
% of Programmed Frequency
INTVCC Voltage
50
3.3
VINTVCC–0.3
V
150
%
3.6
3.9
V
%
Power Good Range
VIN > 4V
–7.5
–11
RPGOOD
Power Good Resistance
PGOOD RDS(ON) at 2mA
275
350
tPGOOD
PGOOD Delay
PGOOD Low to High
PGOOD High to Low
0
32
Cycles
Cycles
0
180
Deg
Deg
Phase Shift Between Channel 1 and Channel VPHASE = 0V
VPHASE = INTVCC, VMODE/SYNC = 0V
2
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. Transient Absolute Maximum Voltages should not be applied for
more than 4% of the switching duty cycle.
Note 3. The LTC3622 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC3622E is guaranteed to meet specified performance from
0°C to 85°C. Specifications over the –40°C to 125°C operating junction
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3622I is guaranteed over the
–40°C to 125°C operating junction temperature range and the LTC3622H
is guaranteed over the -40°C to 150°C operating junction temperature
Ω
range. High junction temperatures degrade operating lifetimes; operating
lifetime is derated for junction temperatures greater than 125°C. 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 environment
factors.
Note 4. The quiescent current in active mode does not include switching
loss of the power FETs.
Note 5. The LTC3622 is tested in a proprietary test mode that connects
VFB to the output of error amplifier.
Note 6. TJ is calculated from the ambient TA and power dissipation PD
according to the following formula: TJ = TA + (PD • θJA)
Rev D
For more information www.analog.com
5
LTC3622/
LTC3622-2/LTC3622-23/5
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
VIN1 = VIN2 = 12V, TA = 25°C, unless otherwise noted.
Efficiency vs Load Current at
Dropout Operation
Efficiency vs Load Current
90
90
90
80
80
80
70
70
70
60
50
40
30
60
50
40
20
VIN = 5V
10 100% Duty Cycle
fSW = 2.25MHz
0
0.0001
0.001
0.01
0.1
LOAD CURRENT (A)
1
3622 G01
VOUT Efficiency vs Input Voltage
Above and Below Dropout
96
ILOAD = 100µA
ILOAD = 1mA
36
24
6.5
8.5 10.5 12.5 14.5 16.5 18.5
INPUT VOLTAGE (V)
IQ (µA)
VIN = 12V
VOUT = 1.8V
fSW = 1MHz
Burst Mode OPERATION
0
0.001
0.01
0.1
LOAD CURRENT (A)
IQ Burst Mode OPERATION
IQ SHUT DOWN
2
1
1
4
70
3622 G05
6
8 10 12 14
INPUT VOLTAGE (V)
16
18
3622 G07
VOUT = 2.5V
fSW = 1MHz
Burst Mode OPERATION
0
2
4 6
8 10 12 14
INPUT VOLTAGE (V)
16
18
3622 G06
Pulse-Skipping Mode Operation
SW
10V/DIV
SW
10V/DIV
VOUT
AC-COUPLED
50mV/DIV
VOUT
AC-COUPLED
20mV/DIV
IL
100mA/DIV
4µs/DIV
2
80
75
IL
200mA/DIV
0
85
Burst Mode Operation
5
0
10mA LOAD
1A LOAD
90
30
10
1
3622 G03
Efficiency vs Input Voltage
95
40
IQ vs VIN
3
0.001
0.01
0.1
LOAD CURRENT (A)
3622 G02
50
3622 G04
4
0
0.0001
1
60
20
VOUT = 4.25V
fSW = 1MHz
Burst Mode OPERATION
4.5
VOUT = 2.5V
VOUT = 3.3V
VIN = 12V
fSW = 2.25MHz
Burst Mode OPERATION
30
10
70
48
0
2.5
40
80
60
12
50
Efficiency vs Load Current
EFFICIENCY (%)
EFFICIENCY (%)
72
60
20
90
ILOAD = 10mA
84
Burst Mode OPERATION
PULSE SKIP
30
EFFICIENCY (%)
VOUT = 2.5V
VOUT = 5V
20
VIN = 12V
10 fSW = 1MHz
Burst Mode OPERATION
0
0.0001
0.001
0.01
0.1
LOAD CURRENT (A)
100
EFFICIENCY (%)
EFFICIENCY (%)
100
EFFICIENCY (%)
100
VIN = 12V
VOUT = 2.5V
Burst Mode OPERATION
IOUT = 75mA
3622 G08
4µs/DIV
3622 G09
VIN = 12V
VOUT = 2.5V
PULSE-SKIPPING MODE
IOUT = 10mA
Rev D
6
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step
VIN1 = VIN2 = 12V, TA = 25°C, unless otherwise noted.
Start-Up Operation
1500
RUN
5V/DIV
1400
IL
200mA/DIV
VOUT
1V/DIV
IL
500mA/DIV
PGOOD
2V/DIV
40µs/DIV
3622 G10
3622 G11
50µs/DIV
OSCILLATOR FREQUENCY (kHz)
VOUT
AC-COUPLED
200mV/DIV
600.5
2.35
2.30
2.25
2.20
2.15
2.10
598.5
16
18
3622 G13
PMOS CHANNEL 1
PMOS CHANNEL 2
NMOS CHANNEL 1
NMOS CHANNEL 2
4
300
200
0 25 50 75 100 125 150
TEMPERATURE (°C)
3622 G16
200
3622 G12
PMOS CH1 RDS(ON)
PMOS CH2 RDS(ON)
NMOS CH1 RDS(ON)
NMOS CH2 RDS(ON)
400
300
100
Load Regulation
5
400
150
RDS(ON) vs Input Voltage
0
2
4
3622 G14
RDS(ON) vs Temperature
–50 –25
700
200
597.0
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
500
100
800
598.0
∆VOUT (%)
RDS(ON) (mΩ)
600
599.0
0.5
PULSE SKIP
Burst Mode OPERATION
3
0.3
2
0.2
1
0.1
0
–1
–0.2
–0.3
Line Regulation
VOUT = 2.5V
ILOAD = 500mA
fSW = 1MHz
PULSE-SKIPPING OPERATION
–0.4
3622 G17
18
3622 G15
0
V = 12V
–3 VIN = 3.3V
OUT
–4 PULSE SKIPPING OPERATION
fSW = 1MHz
–5
0
0.2
0.4
0.6
0.8
LOAD CURRENT (A)
1.2
16
–0.1
–2
1.0
6
8 10 12 14
INPUT VOLTAGE (V)
0.4
∆VOUT (%)
700
6
8 10 12 14
INPUT VOLTAGE (V)
900
500
597.5
2.05
4
1000
599.5
RDS(ON) (mΩ)
2.40
2
1100
600
600.0
REFERENCE VOLTAGE (mV)
OSCILLATOR FREQUENCY (MHz)
2.45
0
1200
Reference Voltage
vs Temperature
2.50
2.00
1300
600 VIN = 12V
fSW = 1MHz
500
–100 –50
0
50
100
TEMPERATURE (°C)
VIN = 12V
VOUT = 3.3V
Burst Mode OPERATION
LOAD STEP FROM 100mA TO 1A
Oscillator Frequency
vs Supply Voltage
Oscillator Frequency
vs Temperature
–0.5
0
3
6
9
12
INPUT VOLTAGE (V)
15
18
3622 G18
Rev D
For more information www.analog.com
7
LTC3622/
LTC3622-2/LTC3622-23/5
TYPICAL PERFORMANCE CHARACTERISTICS
IQ vs Temperature
SLEEP
SHUTDOWN
NMOS1
NMOS2
PMOS1
PMOS2
45000
40000
12
35000
SW LEAKAGE (nA)
QUIESCENT CURRENT (µA)
14
VOUT vs Load Current
Switch Leakage vs Temperature
50000
10
8
6
4
5
4
30000
VOUT (V)
16
VIN1 = VIN2 = 12V, TA = 25°C, unless otherwise noted.
25000
20000
2
15000
10000
1
5000
2
3
ILIM = GND
ILIM = INTVCC
0
0
–100
–50
0
50
100
TEMPERATURE (°C)
150
200
–5000
–50 –25
3622 G19
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
0
0.5
3622 G20
Sync Mode Out-Of-Phase
Operation
Out-Of-Phase Operation
1
1.5
LOAD CURRENT (A)
2
3622 G21
ILIM vs Input Voltage
2.0
EXTERNAL
CLOCK
2V/DIV
SW1
10V/DIV
1.8
1.6
1.4
SW2
10V/DIV
ILIM (A)
SW1
10V/DIV
SW2
10V/DIV
1.2
1.0
0.8
0.6
200ns/DIV
VIN = 12V
VOUT = 2.5V, VOUT = 3.3V
L1 = 4.7µH, L2 = 3.3µH
OUT-OF-PHASE OPERATION
3622 G22
200ns/DIV
SYNC MODE OPERATION
EXTERNAL CLOCK PULSE WIDTH
CONTROLS PHASE SHIFT
3622 G23
0.4
TA = 150°C
TA = 25°C
TA = –45°C
0.2
0
0
3
6
9
12
INPUT VOLTAGE (V)
15
18
3622 G24
Rev D
8
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
PIN FUNCTIONS
(DFN/MSOP)
VIN1 (Pin 1/Pin 1): Input Voltage of Channel 1 Step-Down
Regulator. This input also powers the INTVCC LDO.
PGOOD1 (Pin 2/Pin 3): Open Drain Power Good Indicator
for Channel 1.
MODE/SYNC (Pin 3/Pin 4): Burst Mode Select and External
Clock Synchronization of the Step-Down Regulator. Tie
MODE/SYNC to INTVCC for Burst Mode operation with a
400mA peak current clamp. Tie MODE/SYNC to GND for
pulse-skipping operation. Furthermore, connecting this pin
to an external clock will synchronize the switch clock to
the external clock and put the part in pulse-skipping mode.
PHASE (Pin 4/Pin 5): Phase Select Pin. Tie this pin to
ground to run the regulators in phase (0° phase shift)
between SW rising edge of channel 1 and channel 2. Tie
this pin to INTVCC to set 180° phase shift between channels. When this pin is high, the phase shift may also be
set by modulating the duty cycle of external clock on the
MODE/SYNC pin (channel 1 edge synced to rising edge
of external clock, channel 2 edge synced to falling edge of
external clock). See Applications section for more details.
PGOOD2 (Pin 5/Pin 6): Open Drain Power Good Indicator
for Channel 2.
ILIM (Pin 6/Pin 7): Current Limit Select Pin. Tying this pin
to ground sets the full current limit for both channels. Tying
this pin to INTVCC drops the current limit by a factor of 2
for both channels. Biasing this pin to 1V sets the current
on channel 1 to be the full amount, and the current on
channel 2 to be dropped by a factor of 2.
VIN2 (Pin 7/Pin 8): Input Voltage of Channel 2 Step-Down
Regulator. May be a different voltage than VIN1.
SW2 (Pin 8/Pin 9): Switch Node Connection to the Inductor of Channel 2 Step-Down Regulator.
RUN2 (Pin 9/Pin 10): Logic Controlled RUN Input to Channel 2. Do not leave this pin floating. Logic high activates
the step-down regulator.
FB2 (Pin 10/Pin 11): Feedback Input to the Error Amplifier
of Channel 2 Step-Down Regulator. Connect resistor divider
tap to this pin. The output voltage can be adjusted from
0.6V to VIN by: VOUT = 0.6V • [1 + (R2/R1)]. (Figure 2) For
fixed VOUT options, connect the FB pin directly to VOUT.
INTVCC (Pin 11/Pin 12): Low Dropout Regulator. Bypass
with a low ESR capacitor of at least 1µF to ground.
FB1 (Pin 12/Pin 13): Feedback Input to the Error Amplifier
of Channel 1 Step-Down Regulator. Connect resistor divider
tap to this pin. The output voltage can be adjusted from
0.6V to VIN by: VOUT = 0.6V • [1 + (R2/R1)]. (Figure 2) For
fixed VOUT options, connect the FB pin directly to VOUT.
RUN1 (Pin 13/Pin 14): Logic Controlled RUN Input to
Channel 1. Do not leave this pin floating. Logic high activates the step-down regulator.
SW1 (Pin 14/Pin 16): Switch Node Connection to the
Inductor of Channel 1 Step-Down Regulator.
GND (Pin 15/Pin 17): Ground for Power and Signal Ground.
The exposed pad must be connected to PCB ground for
rated electrical and rated thermal performance.
SVIN (NA/Pin 2): Signal VIN Pin. This input powers the
INTVCC. May be a different voltage than either VIN1 or
VIN2. Connect SVIN to either VIN1 or VIN2 , whichever one
is higher. For applications where it is not known which VIN
is higher, connect external diode between SVIN to both VIN1
and VIN2 to ensure that SVIN is less than a diode drop from
the higher of VIN1 or VIN2.
Rev D
For more information www.analog.com
9
LTC3622/
LTC3622-2/LTC3622-23/5
BLOCK DIAGRAM
VIN1
0.5ms
SOFT-START
0.6V
FB1
+
+
–
SLOPE
COMPENSATION
ERROR
AMPLIFIER
+
BURST
COMPARATOR
+
MAIN
I-COMPARATOR
–
–
FIXED VOUT
BUCK
LOGIC
AND
GATE DRIVE
OVERCURRENT
COMPARATOR
VIN–5V
+
–
SW1
INTVCC
RUN1
PGOOD1
REVERSE
CURRENT
COMPARATOR
+
–
GND
CHANNEL 1
CLK1
MODE/SYNC
INTVCC
CURRENT LIMIT
SELECT
OSCILLATOR
PHASE
LDO
ILIM
CLK2
SVIN (MSOP ONLY)
CHANNEL 2
SAME AS CHANNEL 1
FB2
SW2
RUN2
PGOOD2
VIN2
3622 BD
Rev D
10
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
OPERATION
The LTC3622 is a dual high efficiency monolithic stepdown regulator, which uses a constant frequency, peak
current mode architecture. It operates through a wide VIN
range and regulates with ultralow quiescent current. The
operation frequency is set at either 2.25MHz or 1MHz and
can be synchronized to an external oscillator ±50% of the
inherent frequency. To suit a variety of applications, the
selectable MODE/SYNC pin allows the user to trade off
output ripple for efficiency.
For each channel, the output voltage is set by an external
divider returned to the FB pin. An error amplifier compares
the divided output voltage with a reference voltage of
0.6V and adjusts the peak inductor current accordingly.
Overvoltage and undervoltage comparators will pull the
PGOOD output low if the output voltage is not within 7.5%
of the programmed value. The PGOOD output will go high
immediately after achieving regulation and will go low 32
clock cycles after falling out of regulation.
Main Control Loop
During normal operation, the top power switch (P-channel
MOSFET) is turned on at the beginning of a clock cycle.
The inductor current is allowed to ramp up to a peak level.
Once the level is reached, the top power switch is turned
off and the bottom switch (N-channel MOSFET) is turned
on until the next clock cycle. The peak current level is controlled by the internally compensated ITH voltage, which is
the output of the error amplifier. This amplifier compares
the FB voltage to the 0.6V internal reference. When the
load current increases, the FB voltage decreases slightly
below the reference, which causes the error amplifier to
increase the ITH voltage until the average inductor current
matches the new load current.
The main control loop is shut down by pulling the RUN
pin to ground.
Low Current Operation
Two discontinuous conduction modes (DCM) are available
to control the operation of the LTC3622 at low currents.
Both modes, Burst Mode operation and pulse-skipping
mode, automatically switch from continuous operation to
the selected mode when the load current is low.
To optimize efficiency, Burst Mode operation can be selected by tying the MODE/SYNC pin to INTVCC. In Burst
Mode operation, the peak inductor current is set to be
at least 400mA, even if the output of the error amplifier
demands less. Thus, when the switcher is on at relatively
light output loads, FB voltage will rise and cause the ITH
voltage to drop. Once the ITH voltage drops low enough,the
switcher goes into sleep mode with both power switches off.
The switchers remain in this sleep state until the external
load pulls the output voltage below its regulation point.
When both channels are in sleep mode, the part draws an
ultralow 5µA of quiescent current from VIN.
To minimize VOUT ripple, pulse-skipping mode can be
selected by grounding the MODE/SYNC pin. In LTC3622,
pulse-skipping mode is implemented similarly to Burst
Mode operation with the peak inductor current set to be
at above 66mA. This results in lower ripple than in Burst
Mode operation with the trade-off being slightly lower
efficiency.
High Duty Cycle/Dropout Operation
When the input supply voltage decreases towards the output
voltage, the duty cycle increases and slope compensation
is required to maintain the fixed switching frequency. The
LTC3622 has internal circuitry to accurately maintain the
peak current limit (ILIM) of 1.8A even at high duty cycles.
As the duty cycle approaches 100%, the LTC3622 enters
dropout operation. During dropout, the part will transition
in and out of sleep mode depending on the output load
current. This significantly reduces the quiescent current,
thus prolonging the use of the input supply.
Rev D
For more information www.analog.com
11
LTC3622/
LTC3622-2/LTC3622-23/5
OPERATION
VIN Overvoltage Protection
In order to protect the internal power MOSFET devices
against transient voltage events, the LTC3622 constantly
monitors the VIN1 and VIN2 pins for an overvoltage condition. When VIN1 or VIN2 rise above 18.5V, both regulators
suspend operation by shutting off both power MOSFETs.
Once VIN drops below 18.2V, the regulator immediately
resumes normal operation. The regulators execute softstart when exiting an overvoltage condition.
Low Supply Operation
The LTC3622 incorporates undervoltage lockout circuits
which shut down the part when the input voltages drop
below 2.5V. As the input voltages rise slightly above the
undervoltage threshold, the switchers will begin basic operation. However, the RDS(ON) of the top and bottom switch
of each channel will be slightly higher than that specified
in the electrical characteristics due to lack of gate drive.
Refer to graph of RDS(ON) versus VIN for more details.
Crosstalk can generally be avoided by carefully choosing
the phase shift such that the SW edges do not coincide.
However, there are often situations where this is unavoidable, such as when both channels are operating at near
50% duty cycle. In such cases, the optimized phase shift
can be set by modulating the duty cycle of external clock
on the MODE/SYNC pin (channel 1 edge synced to rising
edge of external clock, channel 2 edge synced to falling
edge of external clock), while keeping the PHASE pin voltage high. Figure 1 shows a 90° phase shifting between
two channels. Table 1 shows the phase selection by the
PHASE pin.
EXTERNAL
CLOCK
SW1
SW2
Phase Selection
500ns/DIV
The two channels of LTC3622 can operate in phase, 180°
out-of-phase (anti-phase) depending on the state of PHASE
pin- low, or high, respectively. Anti-phase generally reduces input voltage and current ripple. Crosstalk between
switch nodes SW1, SW2 and components or sensitive
lines connected to FBx, can sometimes cause unstable
switching waveforms and unexpectedly large input and
output voltage ripple.
The situation improves if rising and falling edges of the
switch nodes are timed carefully not to coincide. Depending
on the duty cycle of the two channels, choose the phase
difference between the channels to keep edges as far away
from each other as possible.
3622 F01
Figure 1. 90° Phase Shift Set by External Clock
Table 1. Phase Selection
NO EXTERNAL CLK
EXTERNAL CLK
PHASE = 0
0° Phase Shift
0° Phase Shift
PHASE = INTVCC
180° Phase Shift
Phase Shift Determined by
Clock Edges
Soft-Start
The LTC3622 has a 500µs soft-start ramp for each channel
when enabled. During soft-start operation, the switchers
operate in pulse-skipping mode.
Rev D
12
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
APPLICATIONS INFORMATION
Output Voltage Programming
For non-fixed output voltage parts, the output voltage is
set by external resistive dividers according to the following equation:
⎛ R2 ⎞
VOUT = 0.6V • ⎜ 1+
⎟
⎝ R1 ⎠
The resistive divider allows the FB pin to sense a fraction
of the output voltage as shown in Figure 2.
For fixed VOUT parts, tie FB directly to VOUT, as R2 and R1
are matched internal resistors.
VOUT
R2
LTC3622 FB
CFF
R1
GND
Output Capacitor (COUT) Selection
The selection of COUT is determined by the effective series
resistance (ESR) that is required to minimize voltage ripple
and load step transients as well as the amount of bulk
capacitance that is necessary to ensure that the control
loop is stable. Loop stability can be checked by viewing
the load transient response. The output ripple, ΔVOUT, is
determined by:
3622 F02
Figure 2. Setting the Output Voltage
Input Capacitor (CIN) Selection
The input capacitance, CIN, is needed to filter the square
wave current at the drain of the top power MOSFET. To
prevent large voltage transients from occurring, a low
ESR input capacitor sized for the maximum RMS current
should be used. The RMS current calculation is different
if the part is used in in-phase or out-of-phase.
For "in phase", when VOUT1 = VOUT2
Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life which
makes it advisable to further derate the capacitor, or choose
a capacitor rated at a higher temperature than required.
Several capacitors may also be paralleled to meet size or
height requirements in the design. For low input voltage
applications, sufficient bulk input capacitance may be
needed to minimize transient effects during output load
changes.
VOUT (VIN – VOUT )
VIN
This formula has a maximum at VIN = 2VOUT. This simple
worst case is commonly used to determine the highest IRMS.
For out-of-phase case, the ripple current can be lower than
the "in phase" current. The maximum current typically occurs when VOUT1 – VIN/2 = VOUT2 or when VOUT2 – VIN/2
= VOUT1. As a good rule of thumb, the amount of worst
case ripple is about 75% of the worst case ripple in the
in-phase mode. Also note that when VOUT1 = VOUT2 = VIN/2
and I1 = I2, the input current ripple is at its minimum.
⎛
⎞
1
ΔVOUT < ΔI L ⎜
+ ESR ⎟
⎝ 8 • ƒ • COUT
⎠
The output ripple is highest at maximum input voltage since
IL increases with input voltage. Multiple capacitors placed
in parallel may be needed to meet the ESR and RMS current
handling requirements. Dry tantalum, special polymer and
hybrid conductive polymer capacitors are very low ESR but
have lower capacitance density than other types. Tantalum
capacitors have the highest capacitance density but it is
importance to only use types that have been surge tested
for use in switching power supplies. Aluminum electrolytic
capacitors have significantly higher ESR, but can be used
in cost-sensitive applications provided that consideration
is given to ripple current ratings and long-term reliability.
Ceramic capacitors have excellent low ESR characteristics
and small footprints.
Using Ceramic Input and Output Capacitors
Higher capacitance value, lower cost ceramic capacitors
are now becoming available in smaller case sizes. Their
high ripple current, high voltage rating and low ESR make
them ideal for switching regulator applications. However,
care must be taken when these capacitors are used at
the input and output. When a ceramic capacitor is used
Rev D
For more information www.analog.com
13
LTC3622/
LTC3622-2/LTC3622-23/5
APPLICATIONS INFORMATION
at the input and the power is supplied by a wall adapter
through long wires, a load step at the output can induce
ringing at the VIN input. At best, this ringing can couple to
the output and be mistaken as loop instability. At worst,
a sudden inrush of current through the long wires can
potentially cause a voltage spike at VIN large enough to
damage the part.
When choosing the input and output ceramic capacitors,
choose the X5R and X7R dielectric formulations. These
dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size.
Since the ESR of a ceramic capacitor is so low, the input
and output capacitor must instead fulfill a charge storage
requirement. During a load step, the output capacitor must
instantaneously supply the current to support the load
until the feedback loop raises the switch current enough
to support the load. Typically, five cycles are required to
respond to a load step, but only in the first cycle does the
output voltage drop linearly. The output droop, VDROOP, is
usually about three times the linear drop of the first cycle.
Thus, a good place to start with the output capacitor value
is approximately:
COUT = 3
ΔIOUT
ƒ O • VDROOP
More capacitance may be required depending on the duty
cycle and load step requirements. In most applications,
the input capacitor is merely required to supply high
frequency bypassing, since the impedance to the supply
is very low. A 10µF ceramic capacitor is usually enough
for these conditions. Place this input capacitor as close
to the VIN1 and VIN2 pins as possible.
Output Power Good
When the LTC3622’s output voltages are within the ±7.5%
window of the regulation point, the output voltages are good
and the PGOOD pins are pulled high with external resistors.
Otherwise, internal open-drain pull-down devices (275Ω)
will pull the PGOOD pins low. To prevent unwanted PGOOD
glitches during transients or dynamic VOUT changes, the
LTC3622’s PGOOD falling edge includes a blanking delay
of approximately 32 switching cycles.
Frequency Synchronization Capability
The LTC3622 has the capability to synchronize to a ±50%
range of the internal programmed frequency. It takes
several cycles of external clock to engage the sync mode,
and roughly 2μs for the part to detect the absence of the
external clock signal. Once engaged in sync, the LTC3622
immediately runs at the external clock frequency.
Inductor Selection
Given the desired input and output voltages, the inductor
value and operating frequency determine the ripple current:
⎛
V
VOUT ⎞
⎟
ΔI L = OUT ⎜⎜ 1–
ƒ • L ⎝ VIN(MAX) ⎟⎠
Lower ripple current reduces power losses in the inductor,
ESR losses in the output capacitors and output voltage
ripple. Highest efficiency operation is obtained at low
frequency with small ripple current. However, achieving
this requires a large inductor. There is a trade-off between
component size, efficiency and operating frequency.
A reasonable starting point is to choose a ripple current
that is about 50% of IOUT(MAX). To guarantee that ripple
current does not exceed a specified maximum, the inductance should be chosen according to:
L=
⎛
VOUT ⎞
⎜⎜ 1–
⎟
ƒ • ΔI L(MAX) ⎝ VIN(MAX) ⎟⎠
VOUT
Once the value for L is known, the type of inductor must
be selected. Actual core loss is independent of core size
for a fixed inductor value, but is very dependent on the
inductance selected. As the inductance or frequency increases, core loss decreases. Unfortunately, increased
inductance requires more turns of wire and therefore
copper losses increase.
Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can
concentrate on copper loss and preventing saturation.
Ferrite core material saturates “hard,” which means that
inductance collapses abruptly when the peak design current
is exceeded. This results in an abrupt increase in inductor
Rev D
14
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
APPLICATIONS INFORMATION
ripple current and consequent output voltage ripple. Do
not allow the core to saturate!
Different core materials and shapes change the size/current and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials are
small and don’t radiate much energy, but generally cost
more than powdered iron core inductors with similar
characteristics. The choice of which style inductor to use
mainly depends on the price versus size requirements
and any radiated field/EMI requirements. New designs for
surface mount inductors are available from Toko, Vishay,
NEC/Tokin, Cooper, TDK and Würth Elektronik. Refer to
Table 2. for more details.
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to the ΔILOAD • ESR, where ESR is the effective series
Table 2. Inductor Selection Table
INDUCTOR
INDUCTANCE
(μH)
DCR
(mΩ)
MAX CURRENT
(A)
DIMENSIONS
(mm)
HEIGHT
(mm)
MANUFACTURER
IHLP-1616BZ-11 Series
1.0
2.2
4.7
24
61
95
4.5
3.25
1.7
4.3 × 4.7
4.3 × 4.7
4.3 × 4.7
2
2
2
IHLP-2020BZ-01 Series
1
2.2
3.3
4.7
5.6
6.8
18.9
45.6
79.2
108
113
139
7
4.2
3.3
2.8
2.5
2.4
5.4 × 5.7
5.4 × 5.7
5.4 × 5.7
5.4 × 5.7
5.4 × 5.7
5.4 × 5.7
2
2
2
2
2
2
FDV0620 Series
1
2.2
3.3
4.7
18
37
51
68
5.7
4
3.2
2.8
6.7 × 7.4
6.7 × 7.4
6.7 × 7.4
6.7 × 7.4
2
2
2
2
MPLC0525L Series
1
1.5
2.2
16
24
40
6.4
5.2
4.1
6.2 × 5.4
6.2 × 5.4
6.2 × 5.4
2.5
2.5
2.5
HCM0703 Series
1
1.5
2.2
3.3
4.7
9
14
18
28
37
11
9
8
6
5.5
7 × 7.4
7 × 7.4
7 × 7.4
7 × 7.4
7 × 7.4
3
3
3
3
3
RLF7030 Series
1
1.5
2.2
3.3
4.7
6.8
8.8
9.6
12
20
31
45
6.4
6.1
5.4
4.1
3.4
2.8
6.9 × 7.3
6.9 × 7.3
6.9 × 7.3
6.9 × 7.3
6.9 × 7.3
6.9 × 7.3
3.2
3.2
3.2
3.2
3.2
3.2
TDK
www.tdk.com
WE-TPC 4828 Series
1.2
1.8
2.2
2.7
3.3
3.9
4.7
17
20
23
27
30
47
52
3.1
2.7
2.5
2.35
2.15
1.72
1.55
4.8 × 4.8
4.8 × 4.8
4.8 × 4.8
4.8 × 4.8
4.8 × 4.8
4.8 × 4.8
4.8 × 4.8
2.8
2.8
2.8
2.8
2.8
2.8
2.8
Würth Elektronik
www.we-online.com
XFL4020 Series
1.0
1.5
2.2
3.3
4.7
10.8
14.4
21.35
34.8
52.2
8
6.7
6.0
3.9
3.6
4×4
4×4
4×4
4×4
4×4
2
2
2
2
2
Vishay
www.vishay.com
Toko
www.toko.com
NEC/Tokin
www.nec-tokin.com
Cooper Bussmann
www.cooperbussmann.com
Coilcraft
www.coilcraft.com
Rev D
For more information www.analog.com
15
LTC3622/
LTC3622-2/LTC3622-23/5
APPLICATIONS INFORMATION
resistance of COUT. ΔILOAD also begins to charge or discharge COUT generating a feedback error signal used by the
regulator to return VOUT to its steady state value. During
this recovery time, VOUT can be monitored for overshoot
or ringing that indicates a stability problem.
The initial output voltage step may not be within the bandwidth of the feedback loop, so the standard second order
overshoot/DC ratio cannot be used to determine phase
margin. In addition, a feedforward capacitor can be added
to improve the high frequency response, shown in Figure 2.
Capacitor CFF provides phase lead by creating a high frequency zero with R2, which improves the phase margin.
The output voltage settling behavior is related to the stability of the closed-loop system and demonstrates the actual
overall supply performance. For a detailed explanation of
optimizing the compensation components, including a
review of control loop theory, refer to Application Note 76.
In some applications, a more severe transient can be caused
by switching in loads with large (>1µF) input capacitors.
The discharge input capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
deliver enough current to prevent this problem if the switch
connecting to load has low resistance and is driven quickly.
The solution is to limit the turn-on speed of the load switch
driver. A Hot Swap controller is designed specifically for
this purpose and usually incorporates current limiting,
short-circuit protection and soft-starting.
Efficiency Considerations
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Percent efficiency can
be expressed as:
% Efficiency = 100% – (L1 + L2 + L3 + …)
where L1, L2 etc. are the individual losses as a percentage of input power. Although all dissipative elements in
the circuit produce losses, three main sources usually
account for most of the losses in LTC3622 circuit: 1) I2R
losses, 2) switching and biasing losses, 3) other losses.
1. I2R losses are calculated from the DC resistances of the
internal switches, RSW, and external inductor, RL. In
continuous mode, the average output current flows
through inductor L but is “chopped” between the
internal top and bottom power MOSFETs. Thus, the
series resistance looking into the SW pin is a function
of both top and bottom MOSFET RDS(ON) and the duty
cycle (DC) as follows:
RSW =(RDS(ON)TOP)(DC)+(RDS(ON)BOT)(1 – DC)
The RDS(ON) for both the top and bottom MOSFETs
can be obtained from the Typical Performance Characteristics curves. Thus to obtain I2R losses:
I2R Losses = IOUT2(RSW + RL)
2. The switching current is the sum of the MOSFET driver
and control currents. The power MOSFET driver current results from switching the gate capacitance of the
power MOSFETs. Each time a power MOSFET gate is
switched from low to high to low again, a packet of
charge dQ moves from VIN to ground. The resulting
dQ/dt is a current out of VIN that is typically much
larger than the DC control bias current. In continuous
mode, IGATECHG = fOSC(QT + QB), where QT and QB are
the gate charges of the internal top and bottom power
MOSFETs and fOSC is the switching frequency. The
power loss is thus:
Switching Loss = IGATECHG • VIN
The gate charge loss is proportional to VIN and fOSC
and thus their effects will be more pronounced at
higher supply voltages and higher frequencies.
3. Other “hidden” losses such as transition loss and copper trace and internal load resistances can account
for additional efficiency degradations in the overall
power system. It is very important to include these
“system” level losses in the design of a system. Transition loss arises from the brief amount of time the top
power MOSFET spends in the saturated region during
switch node transitions. The LTC3622 internal power
devices switch quickly enough that these loses are not
significant compared to other sources. These losses
plus other losses, including diode conduction losses
during dead time and inductor core losses, generally
account for less than 2% total additional loss.
Rev D
16
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
APPLICATIONS INFORMATION
Thermal Conditions
In a majority of applications, the LTC3622 does not dissipate much heat due to its high efficiency. However, in
applications where the LTC3622 is running at high ambient temperature, high VIN, high switching frequency, and
maximum output current load, the heat dissipated may
exceed the maximum junction temperature of the part. If
the junction temperature reaches approximately 160°C,
all power switches will be turned off until the temperature
drops about 15°C cooler.
To prevent the LTC3622 from exceeding the maximum
junction temperature, the user needs to do some thermal
analysis. The goal of the thermal analysis is to determine
whether the power dissipated exceeds the maximum
junction temperature of the part. The temperature rise is
given by:
TRISE = PD • θJA
As an example, consider the case when the LTC3622 is
used in applications where VIN = 12V, IOUT = IOUT1 = IOUT2
= 1A, ƒ = 2.25MHz, VOUT = VOUT1 = VOUT2 = 1.8V. The
equivalent power MOSFET resistance RSW is:
R SW = RDS(ON)TOP •
= 370mΩ •
The active current through VIN at 2.25MHz without load
is about 10mA, which includes switching and internal
biasing current loss, and transition loss. Therefore, the
total power dissipated by the part is:
PD = 2 • IOUT2 • RSW + VIN • IIN(Q)
= 2 • 1A2 • 183mΩ + 12V • 10mA
= 486mW
For the DFN package, the θJA is 40°C/W. Therefore, the
junction temperature of the regulator operating at 25°C
ambient temperature is approximately:
TJ = 486mW • 40°C/W + 25°C = 44.4°C
Remembering that the above junction temperature is
obtained from an RDS(ON) at 25°C, we might recalculate
the junction temperature based on a higher RDS(ON) since
it increases with temperature. Redoing the calculation
assuming that RSW increased 5% at 44.4°C yields a new
junction temperature of 45.4°C. If the application calls
for a higher ambient temperature and/or higher switching
frequency, care should be taken to reduce the temperature
rise of the part by using a heat sink or air flow.
⎞
⎛ V
+ RDS(ON)BOT • ⎜ 1– OUT ⎟
VIN
VIN ⎠
⎝
VOUT
1.8V
⎛ 1.8V ⎞
+ 150mΩ • ⎜ 1–
⎟ = 183mΩ
⎝
12V
12V ⎠
Rev D
For more information www.analog.com
17
LTC3622/
LTC3622-2/LTC3622-23/5
APPLICATIONS INFORMATION
Board Layout Considerations
4. Solder the exposed pad (Pin 15 for DFN, Pin 17 for
MSOP) on the bottom of the package to the GND
plane. Connect this GND plane to other layers with
thermal vias to help dissipate heat from the LTC3622.
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3622 (refer to Figure 3). Check the following in
the layout:
5. Keep sensitive components away from the SW pin. The
input capacitor, CIN, feedback resistors, and INTVCC
bypass capacitors should be routed away from the
SW trace and the inductor.
1. Do the capacitors CIN connect to the VIN and GND as
close as possible? These capacitors provide the AC
current to the internal power MOSFETs and their drivers.
Does CVCC connect to INTVCC as close as possible?
6. A ground plane is highly recommended.
2. Are COUT and L closely connected? The (–) plate of
COUT returns current to GND and the (–) plate of CIN.
7. Flood all unused areas on all layers with copper, which
reduces the temperature rise of power components.
These copper areas should be connected to GND.
3. The resistive divider, R1 and R2, must be connected
between the (+) plate of COUT and a ground line terminated near GND. The feedback signal VFB should
be routed away from noisy components and traces,
such as the SW line, and its trace should be minimized.
Keep R1 and R2 close to the IC.
GND
VIN
COUT1
VIAS TO
GROUND
PLANE
L1
CIN
SW1
CIN
SW2
VIAS TO
GROUND
PLANE
L2
COUT2
VIN
GND
VIAS TO
GROUND
PLANE
36222 F03
Figure 3. Layout Diagram
Rev D
18
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
APPLICATIONS INFORMATION
Design Example
Using standard value of 3.3µH and 2.7µH for inductors
results in maximum ripple currents of:
As a design example, consider using the LTC3622 in an
application with the following specifications:
ΔI L1 =
VIN1 = VIN1 = 10.8V to 13.2V
VOUT1 = 5V
VOUT2 = 3.3V
IOUT1(MAX) = 1A
IOUT2(MAX) = 1A
IOUT(MIN) = 0
fSW = 2.25MHz
3.3V
⎛
3.3V ⎞
⎜ 1–
⎟ = 0.41A
2.25MHz • 2.7µH ⎝ 13.2V ⎠
CIN should be sized for a maximum current rating of:
Given the internal oscillator of 2.25MHz, we can calculate
the inductors value for about 40% ripple current at maximum VIN:
⎛ 5 ⎞ 13.2
I RMS1 = 1A ⎜
– 1 = 0.49A
⎟
⎝ 13.2 ⎠
5
⎛
⎞⎛
5V
5V ⎞
L1= ⎜
⎟ ⎜ 1–
⎟ = 3.4µH
⎝ 2.25MHz • 0.4A ⎠ ⎝ 13.2V ⎠
⎛ 3.3 ⎞ 13.2
– 1 = 0.43A
I RMS2 = 1A ⎜
⎟
⎝ 13.2 ⎠ 3.3
⎛
⎞⎛
3.3V ⎞
3.3V
L2 = ⎜
⎟ ⎜ 1–
⎟ = 2.75µH
⎝
⎝
⎠
⎠
13.2V
2.25MHz
•
0.4A
CIN
10µF
⎛
5V ⎞
⎜ 1–
⎟ = 0.42A
2.25MHz • 3.3µH ⎝ 13.2V ⎠
COUT will be selected based on the ESR that is required to
satisfy the output voltage ripple requirement and the bulk
capacitance needed for loop stability. For this design, a
22µF ceramic capacitor will be used.
Because efficiency is important at both high and low load
current, Burst Mode operation will be utilized.
VIN
17V MAX
ΔI L2 =
5V
Decoupling the VIN1 and VIN2 pins with 10µF ceramic
capacitors is adequate for most applications.
VIN1
INTVCC
VIN2 MODE/SYNC
RUN1
PHASE
RUN2
ILIM
LTC3622-2
C1
1µF
PGOOD1 PGOOD2
3.3µH
VOUT1
5V
1A
COUT1
22µF
22pF
SW2
SW2
2.7µH
619k
619k
FB2
84.5k
GND
22pF
FB2
137k
VOUT2
3.3V
1A
COUT2
22µF
3622 F04
Figure 4. 5V/3.3V VOUT Burst Mode Operation Application
Rev D
For more information www.analog.com
19
LTC3622/
LTC3622-2/LTC3622-23/5
TYPICAL APPLICATIONS
5V/3.3V VOUT, Burst Mode Operation, In-Phase Switching
VIN
17V MAX
CIN
10µF
VIN1
INTVCC
VIN2 MODE/SYNC
RUN1
PHASE
RUN2
ILIM
LTC3622-2
C1
1µF
PGOOD1 PGOOD2
6.8µH
VOUT1
5V
1A
22pF
COUT1
22µF
SW1
SW2
FB1
FB2
3.3µH
619k
22pF
619k
GND
84.5k
137k
VOUT2
3.3V
1A
COUT2
22µF
3622 TA02
Efficiency vs Load
Load Step Waveform
100
90
IL
500mA/DIV
EFFICIENCY (%)
80
70
60
50
VOUT
AC-COUPLED
200mV/DIV
40
30
20
10
VOUT = 5V
VOUT = 3.3V
VIN = 12V
fSW = 2.25MHz
Burst Mode OPERATION
0
0.0001
0.001
0.01
0.1
LOAD CURRENT (A)
40µs/DIV
VIN = 12V
VOUT1 = 5V
ILOAD = 5mA → 500mA
Burst Mode OPERATION
fSW = 2.25MHz
1
3622 TA02a
3622 TA02b
Dual Output Regulators from Multiple Input Sources
1µF
VIN1
12V
SVIN
VIN1
CIN1
10µF
RUN2
PHASE
ILIM
3.3µH
COUT1
22µF
22pF
CIN2
10µF
LTC3622
INTVCC
MODE/SYNC
VOUT1
5V
1A
VIN2
5V
VIN2
RUN1
PGOOD1
PGOOD2
SW1
SW2
FB1
FB2
C1
1µF
1µH
604k
604k
GND
82.5k
134k
22pF
VOUT2
3.3V
1A
COUT2
22µF
3622 TA06
Rev D
20
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
PACKAGE DESCRIPTION
DE Package
14-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1708 Rev B)
0.70 ±0.05
3.30 ±0.05
3.60 ±0.05
2.20 ±0.05
1.70 ±0.05
PACKAGE
OUTLINE
0.25 ±0.05
0.50 BSC
3.00 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ±0.10
(2 SIDES)
R = 0.115
TYP
8
R = 0.05
TYP
0.40 ±0.10
14
3.30 ±0.10
3.00 ±0.10
(2 SIDES)
1.70 ±0.10
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
PIN 1
TOP MARK
(SEE NOTE 6)
0.200 REF
(DE14) DFN 0806 REV B
7
0.75 ±0.05
1
0.25 ±0.05
0.50 BSC
3.00 REF
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC
PACKAGE OUTLINE MO-229
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
Rev D
For more information www.analog.com
21
LTC3622/
LTC3622-2/LTC3622-23/5
PACKAGE DESCRIPTION
MSE Package
16-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1667 Rev F)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 ±0.102
(.112 ±.004)
5.10
(.201)
MIN
2.845 ±0.102
(.112 ±.004)
0.889 ±0.127
(.035 ±.005)
8
1
1.651 ±0.102
(.065 ±.004)
1.651 ±0.102 3.20 – 3.45
(.065 ±.004) (.126 – .136)
0.305 ±0.038
(.0120 ±.0015)
TYP
16
0.50
(.0197)
BSC
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
0.35
REF
0.12 REF
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
9
NO MEASUREMENT PURPOSE
0.280 ±0.076
(.011 ±.003)
REF
16151413121110 9
DETAIL “A”
0° – 6° TYP
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
4.90 ±0.152
(.193 ±.006)
GAUGE PLANE
0.53 ±0.152
(.021 ±.006)
DETAIL “A”
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
1234567 8
0.50
(.0197)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL
NOT EXCEED 0.254mm (.010") PER SIDE.
0.86
(.034)
REF
0.1016 ±0.0508
(.004 ±.002)
MSOP (MSE16) 0213 REV F
Rev D
22
For more information www.analog.com
LTC3622/
LTC3622-2/LTC3622-23/5
REVISION HISTORY
REV
DATE
DESCRIPTION
A
03/15
Added LTC3622-23/5 Options in Header.
All
Added LTC3622-23/5 to Options Table.
1
Added LTC3622-23/5 to Electrical Characteristics.
Added MSOP-16E Package Options.
B
8/15
PAGE NUMBER
3
1, 2, 3, 22
Added H-Grade Options.
2, 3, 4
Clarified Pin Functions.
8
Clarified Table 2.
14
Added MSOP-16E in #4.
17
Clarified package description to MSE.
2
Clarified Package Description to MSE, 16-Lead MSOP, exposed die pad.
22
C
6/16
Changed ABS Max Rating of RUN1 and RUN2 pins.
2
D
9/18
Clarified RDS(ON) vs Temperature Graph
7
Rev D
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
morebyinformation
www.analog.com
subject to change without notice. No license For
is granted
implication or
otherwise under any patent or patent rights of Analog Devices.
23
LTC3622/
LTC3622-2/LTC3622-23/5
TYPICAL APPLICATION
5V/3.3V Series Output, Burst Mode Operation
VIN
5V TO 17V
INTVCC
CIN
10µF
10k
3.3µH
VOUT1
5V
1A
COUT1
22µF
22pF
VIN1
INTVCC
MODE/SYNC
C1
1µF
RUN1
RUN2
PHASE
ILIM
VIN2
LTC3622-2
PGOOD1 PGOOD2
SW1
SW2
FB1
FB2
1µH
604k
604k
82.5k
GND
134k
22pF
VOUT2
3.3V
1A
COUT2
22µF
3622 TA03
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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LTC3621-2
1A, 17V, 1/2.25MHz, Synchronous Step-Down Regulator 95% Efficiency, VIN: 2.7V to 17V, VOUT(MIN) = 0.6V, IQ = 3.5µA, ISD < 1µA,
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LTC3600
1.5A, 15V, 4MHz Synchronous Rail-to-Rail Single
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LTC3601
15V, 1.5A (IOUT) 4MHz Synchronous Step-Down
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95% Efficiency, VIN: 4.5V to 15V, VOUT(MIN) = 0.6V, IQ = 300µA, ISD < 1µA,
4mm × 4mm QFN-20, MSOP-16E Packages
LTC3603
15V, 2.5A (IOUT) 3MHz Synchronous Step-Down
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4mm × 4mm QFN-20, MSOP-16E Packages
LTC3633A
20V, Dual 3A (IOUT) 4MHz Synchronous Step-Down
DC/DC Converter
95% Efficiency, VIN: 3.6V to 20V, VOUT(MIN) = 0.6V, IQ = 500µA, ISD < 15µA,
4mm × 5mm QFN-28, TSSOP-28E Packages. A Version Up to 20VIN
LTC3605A
20V, 5A (IOUT) 4MHz Synchronous Step-Down
DC/DC Converter
95% Efficiency, VIN: 4V to 20V, VOUT(MIN) = 0.6V, IQ = 2mA, ISD < 15µA,
4mm × 4mm QFN-24 Package. A Version Up to 20VIN
LTC3604
15V, 2.5A (IOUT) 4MHz Synchronous Step-Down
DC/DC Converter
95% Efficiency, VIN: 3.6V to 15V, VOUT(MIN) = 0.6V, IQ = 300µA, ISD < 14µA,
3mm × 3mm QFN-16, MSOP-16E Packages
LTC3624/
LTC3624-2
2A, 17V, 1MHz/2.25MHz Synchronous Step-Down
Regulator
95% Efficiency, VIN: 2.7V to 17V, VOUT(MIN) = 0.6V, IQ = 3.5µA, ISD < 1µA,
3mm × 3mm DFN-8 Package
Rev D
24
09/18(D)
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