LTC4090/LTC4090-5
USB Power Manager with
2A High Voltage Bat-Track
Buck Regulator
DESCRIPTION
FEATURES
Seamless Transition Between Power Sources:
Li-Ion Battery, USB, and 6V to 36V Supply (60V Max)
n 2A Output High Voltage Buck Regulator with
Bat-Track™ Adaptive Output Control (LTC4090)
n Internal 215mW Ideal Diode Plus Optional
External Ideal Diode Controller Provides Low Loss
PowerPath™ When External Supply/ USB Not Present
n Load Dependent Charging from USB Input
Guarantees Current Compliance
n Full Featured Li-Ion Battery Charger
n 1.5A Maximum Charge Current with Thermal Limiting
n NTC Thermistor Input for Temperature Qualified
Charging
n Tiny (3mm × 6mm × 0.75mm) 22-Pin DFN Package
The LTC®4090/LTC4090-5 are USB power managers plus
high voltage Li-Ion/Polymer battery chargers. The devices
control the total current used by the USB peripheral for
operation and battery charging. Battery charge current
is automatically reduced such that the sum of the load
current and the charge current does not exceed the programmed input current limit. The LTC4090/LTC4090-5
also accommodate high voltage power supplies, such as
12V AC/DC wall adapters, Firewire, or automotive power.
n
The LTC4090 provides a Bat-Track adaptive output that
tracks the battery voltage for high efficiency charging from
the high voltage input. The LTC4090-5 provides a fixed 5V
output from the high voltage input to charge single-cell
Li-Ion batteries. The charge current is programmable and an
end-of-charge status output (CHRG) indicates full charge.
Also featured are programmable total charge time, an NTC
thermistor input used to monitor battery temperature while
charging and automatic recharging of the battery.
APPLICATIONS
n
n
n
n
HDD-Based Media Players
Personal Navigation Devices
Other USB-Based Handheld Products
Automotive Accessories
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and Bat-Track, PowerPath and ThinSOT are trademarks of Analog Devices, Inc. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
0.47µF
HIGH (7.5V-36V)
VOLTAGE INPUT
SW
BOOST
HVIN
LTC4090/LTC4090-5 High Voltage
Battery Charger Efficiency
6.8µH
22µF
1µF
90
FIGURE 12 SCHEMATIC
WITH RPROG = 52k
80 NO OUTPUT LOAD
HVOUT
IN
270pF
LTC4090
0.1µF
70
1k
VC
OUT
TIMER
BAT
LOAD
4.7µF
CLPROG
RT
59k
LTC4090
HVPR
4.7µF
USB
40.2k
VOUT (TYP)
VBAT + 0.3V
5V
5V
VBAT
2k
GND
PROG
100k
AVAILABLE INPUT
HV INPUT (LTC4090)
HV INPUT (LTC4090-5)
USB ONLY
BAT ONLY
+
EFFICIENCY (%)
5V WALL
ADAPTER
LTC4090-5
60
50
40
Li-Ion BATTERY
HVIN = 8V
HVIN = 12V
HVIN = 24V
HVIN = 36V
30
20
2.0
2.5
3.5
3.0
VBAT (V)
4.0
4.5
4090 TA01b
4090 TAO1
4090fe
For more information www.linear.com/LTC4090
1
LTC4090/LTC4090-5
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Notes 1, 2, 3, 4)
HVIN, HVEN (Note 9).................................................60V
BOOST.......................................................................56V
BOOST above SW......................................................30V
PG, SYNC...................................................................30V
IN, OUT, HVOUT
t < 1ms and Duty Cycle < 1%.................... –0.3V to 7V
Steady State............................................. –0.3V to 6V
BAT, HPWR, SUSP, VC , CHRG, HVPR............ –0.3V to 6V
NTC, TIMER, PROG, CLPROG...........–0.3V to VCC + 0.3V
IIN, IOUT, IBAT (Note 5)...............................................2.5A
Operating Temperature Range......................–40 to 85°C
Junction Temperature.............................................110°C
Storage Temperature Range....................... –65 to 125°C
ORDER INFORMATION
TOP VIEW
SYNC
1
22 HVEN
PG
2
21 HVIN
RT
3
20 SW
VC
4
19 BOOST
NTC
5
VNTC
6
HVPR
7
16 SUSP
CHRG
8
15 HPWR
PROG
9
14 CLPROG
18 HVOUT
23
GATE 10
BAT 11
17 TIMER
13 OUT
12 IN
DJC PACKAGE
22-LEAD (6mm × 3mm) PLASTIC DFN
TJMAX = 110°C, θJA = 47°C/W
EXPOSED PAD (PIN 23) IS GND, MUST BE SOLDERED TO PCB
http://www.linear.com/product/LTC4090#orderinfo
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4090EDJC#PBF
LTC4090EDJC#TRPBF
4090
22-Lead (6mm × 3mm) Plastic DFN
–40°C to 85°C
LTC4090EDJC-5#PBF
LTC4090EDJC-5#TRPBF
40905
22-Lead (6mm × 3mm) Plastic DFN
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. HVIN = HVEN = 12V, BOOST = 17V, VIN = HPWR = 5V, VBAT = 3.7V,
RPROG = 100k, RCLPROG = 2k and SUSP = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
USB Input Current Limit
VIN
USB Input Supply Voltage
IIN
Input Bias Current
IBAT = 0 (Note 6)
Suspend Mode; SUSP = 5V
l
l
ILIM
Current Limit
HPWR = 5V
HPWR = 0V
l
l
IIN(MAX)
Maximum Input Current Limit
(Note 7)
RON
On-Resistance VIN to VOUT
IOUT = 80mA
VCLPROG
CLPROG Servo Voltage in Current Limit
RCLPROG = 2k
RCLPROG = 1k
ISS
Soft-Start Inrush Current
2
l
l
l
4.35
475
90
0.98
0.98
5.5
V
0.5
50
1
100
mA
µA
500
100
525
110
mA
mA
2.4
A
0.215
W
1.00
1.00
10
1.02
1.02
V
V
mA/µs
4090fe
For more information www.linear.com/LTC4090
LTC4090/LTC4090-5
ELECTRICAL
CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. HVIN = HVEN = 12V, BOOST = 17V, VIN = HPWR = 5V, VBAT = 3.7V,
RPROG = 100k, RCLPROG = 2k and SUSP = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VCLEN
Input Current Limit Enable Threshold
Voltage (VIN - VOUT)
(VIN - VOUT) Rising
(VIN - VOUT) Falling
20
–80
50
–50
80
–20
mV
mV
VUVLO
Input Undervoltage Lockout
VIN Rising
3.6
3.8
4
DVUVLO
Input Undervoltage Lockout Hysteresis
VIN Rising – VIN Falling
l
130
V
mV
High Voltage Regulator
VHVIN
HVIN Supply Voltage
l
6
l
36
VOVLO
HVIN Overvoltage Lockout Threshold
IHVIN
HVIN Bias Current
Shutdown; HVEN = 0.2V
Not Switching, HVOUT = 3.6V
VOUT
Output Voltage with HVIN Present
Assumes HVOUT to OUT Connection,
0 ≤ VBAT ≤ 4.2V (LTC4090)
VOUT
Output Voltage with HVIN Present
fSW
Switching Frequency
tOFF
Minimum Switch Off-Time
ISW(MAX)
Switch Current Limit
Duty Cycle = 5%
VSAT
Switch VCESAT
ISW = 2A
IR
Boost Schottky Reverse Leakage
SW = 10V, HVOUT = 0V
VB(MIN)
Minimum Boost Voltage (Note 8)
IBST
BOOST Pin Current
60
V
38
40
V
0.01
130
0.5
200
µA
µA
3.45
VBAT + 0.3
4.6
V
Assumes HVOUT to OUT Connection
(LTC4090-5)
4.85
5
5.15
V
RT = 8.66k
RT = 29.4k
RT = 187k
2.1
0.9
160
2.4
1.0
200
2.7
1.15
240
MHz
MHz
kHz
60
150
ns
3.5
4.0
A
l
l
3.0
500
mV
0.02
2
µA
1.5
2.1
V
22
35
mA
15
22
60
27
35
100
µA
µA
µA
4.165
4.158
4.200
4.200
4.235
4.242
V
V
465
900
500
1000
535
1080
mA
mA
l
ISW = 1A
Battery Management
IBAT
Battery Drain Current
VBAT = 4.3V, Charging Stopped
Suspend Mode, SUSP = 5V
VIN = 0V, BAT Powers OUT, No Load
VFLOAT
VBAT Regulated Output Voltage
IBAT = 2mA
IBAT = 2mA; 0 ≤ TA ≤ 85°C
ICHG
Constant-Current Mode Charge Current, RPROG = 100k
No Load
RPROG = 50k, 0 ≤ TA ≤ 85°C
ICHG(MAX)
Maximum Charge Current
VPROG
PROG Pin Servo Voltage
kEOC
l
l
l
l
1.5
A
RPROG = 100k
RPROG = 50k
l
l
0.98
0.98
1.00
1.00
1.02
1.02
V
V
Ratio of End-of-Charge Indication
Current to Charge Current
VBAT = VFLOAT (4.2V)
l
0.085
0.1
0.11
mA/mA
ITRKL
Trickle Charge Current
BAT = 2V
35
50
60
2.75
2.9
3.0
VTRKL
Trickle Charge Threshold Voltage
BAT Rising
VCEN
Charge Enable Threshold Voltage
(VOUT – VBAT) Falling; VBAT = 4V
(VOUT – VBAT) Rising; VBAT = 4V
DVRECHRG
Recharge Battery Threshold Voltage
Threshold Voltage Relative to VFLOAT
l
55
80
l
–65
–100
mA
V
mV
mV
–135
mV
4090fe
For more information www.linear.com/LTC4090
3
LTC4090/LTC4090-5
ELECTRICAL
CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. HVIN = HVEN = 12V, BOOST = 17V, VIN = HPWR = 5V, VBAT = 3.7V,
RPROG = 100k, RCLPROG = 2k and SUSP = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
tTIMER
TIMER Accuracy
VBAT = 4.3V
–10
Recharge Time
Percent of Total Charge Time
50
%
Low Battery Trickle Charge Time
Percent of Total Charge Time,
VBAT 38V (typical),
the LTC4090/LTC4090-5 will stop switching, allowing the
output to fall out of regulation.
where VHVIN(MIN) is the minimum input voltage, and
tOFF(MIN) is the minimum switch-off time (150ns). Note
that higher switching frequency will increase the minimum
input voltage. If a lower dropout voltage is desired, a lower
switching frequency should be used.
While the high voltage regulator output is in start-up,
short-circuit, or other overload conditions, the switching
frequency should be chosen according to the following
discussion.
Inductor Selection and Maximum Output Current
For safe operation at inputs up to 60V the switching frequency must be low enough to satisfy VHVIN(MAX) ≥ 40V
according to the following equation. If lower VHVIN(MAX)
is desired, this equation can be used directly.
VHVIN(MAX ) =
VHVOUT + VD
– VD + VSW
fSW • t ON(MIN)
where VHVIN(MAX) is the maximum operating input voltage,
VHVOUT is the high voltage regulator output voltage, VD is
the catch diode drop (~0.5V), VSW is the internal switch
drop (~0.5V at max load), fSW is the switching frequency
(set by RT), and tON(MIN) is the minimum switch-on time
(~150ns). Note that a higher switching frequency will depress the maximum operating input voltage. Conversely,
a lower switching frequency will be necessary to achieve
safe operation at high input voltages.
If the output is in regulation and no short-circuit, start-up, or
overload events are expected, then input voltage transients
of up to 60V are acceptable regardless of the switching
frequency. In this mode, the LTC4090/LTC4090-5 may
A good choice for the inductor value is L = 6.8µH (assuming a 800kHz operating frequency). With this value the
maximum load current will be ~2.4A. The RMS current
rating of the inductor must be greater than the maximum
load current and its saturation current should be about
30% higher. Note that the maximum load current will be
programmed charge current plus the largest expected
application load current. For robust operation in fault
conditions, the saturation current should be ~3.5A. To
keep efficiency high, the series resistance (DCR) should
be less than 0.1W. Table 2 lists several vendors and types
that are suitable.
Table 2. Inductor Vendors
VENDOR URL
PART SERIES
TYPE
Murata
www.murata.com
LQH55D
Open
TDK
www.componenttdk.com
SLF7045
SLF10145
Shielded
Shielded
Toko
www.toko.com
D62CB
D63CB
D75C
D75F
Shielded
Shielded
Shielded
Open
Sumida
www.sumida.com
CR54
CDRH74
CDRH6D38
CR75
Open
Shielded
Shielded
Open
4090fe
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19
LTC4090/LTC4090-5
APPLICATIONS INFORMATION
Catch Diode
The catch diode conducts current only during switch-off
time. Average forward current in normal operation can
be calculated from:
ID(AVG) = IHVOUT
(V – V
)
• HVIN HVOUT
VHVIN
where IHVOUT is the output load current. The only reason to
consider a diode with a larger current rating than necessary
for nominal operation is for the worst-case condition of
shorted output. The diode current will then increase to the
typical peak switch current. Peak reverse voltage is equal
to the regulator input voltage. Use a Schottky diode with a
reverse voltage rating greater than the input voltage. The
overvoltage protection feature in the high voltage regulator
will keep the switch off when VHVIN > 40V which allows
the use of 40V rated Schottky even when VHVIN ranges
up to 60V. Table 3 lists several Schottky diodes and their
manufacturers.
Table 3. Diode Vendors
PART NUMBER
VR
(V)
IAVE
(A)
VF AT 1A
(MV)
VF AT 2A
(MV)
On Semiconductor
MBRM120E
MBRM140
20
40
1
1
530
550
595
Diodes Inc.
B120
B130
B220
B230
DFLS240L
20
30
20
30
40
1
1
2
2
2
500
500
International Rectifier
10BQ030
20BQ030
30
30
1
2
420
500
500
500
470
470
High Voltage Regulator Output Capacitor Selection
The high voltage regulator output capacitor has two
essential functions. Along with the inductor, it filters the
square wave generated at the switch pin to produce the
DC output. In this role it determines the output ripple, and
low impedance at the switching frequency is important.
The second function is to store energy in order to satisfy
transient loads and stabilize the LTC4090/LTC4090-5’s
control loop. Ceramic capacitors have very low equiva-
20
lent series resistance (ESR) and provide the best ripple
performance. A good starting value is:
COUT =
100
VOUT fSW
where fSW is in MHz, and COUT is the recommended
output capacitance in µF. Use X5R or X7R types. This
choice will provide low output ripple and good transient
response. Transient performance can be improved with a
higher value capacitor if the compensation network is also
adjusted to maintain the loop bandwidth. A lower value of
output capacitor can be used to save space and cost but
transient performance will suffer. See the High Voltage
Regulator Frequency Compensation section to choose an
appropriate compensation network.
When choosing a capacitor, look carefully through the
data sheet to find out what the actual capacitance is under
operating conditions (applied voltage and temperature).
A physically larger capacitor, or one with a higher voltage
rating, may be required. High performance tantalum or
electrolytic capacitors can be used for the output capacitor.
Low ESR is important, so choose one that is intended for
use in switching regulators. The ESR should be specified
by the supplier, and should be 0.05W or less. Such a
capacitor will be larger than a ceramic capacitor and will
have a larger capacitance, because the capacitor must be
large to achieve low ESR.
Ceramic Capacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
when used with the high voltage switching regulator due to
their piezoelectric nature. When in Burst Mode operation,
the LTC4090/LTC4090-5’s switching frequency depends
on the load current, and at very light loads the LTC4090/
LTC4090-5 can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LTC4090/
LTC4090-5 operate at a lower current limit during Burst
Mode operation, the noise is typically very quiet to a casual ear. If this is unacceptable, use a high performance
tantalum or electrolytic capacitor at the output.
4090fe
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LTC4090/LTC4090-5
APPLICATIONS INFORMATION
High Voltage Regulator Frequency Compensation
The LTC4090/LTC4090-5 high voltage regulator uses
current mode control to regulate the output. This simplifies loop compensation. In particular, the high voltage
regulator does not require the ESR of the output capacitor
for stability, so you are free to use ceramic capacitors to
achieve low output ripple and small circuit size. Frequency compensation is provided by the components tied to
the VC pin, as shown in Figure 1. Generally a capacitor
(CC) and a resistor (RC) in series to ground are used. In
addition, there may be a lower value capacitor in parallel.
This capacitor (CF) is not part of the loop compensation
but is used to filter noise at the switching frequency, and
is required only if a phase-lead capacitor is used or if the
output capacitor has high ESR.
Loop compensation determines the stability and transient
performance. Designing the compensation network is a bit
complicated and the best values depend on the application
and in particular the type of output capacitor. A practical
approach is to start with the front page schematic and
tune the compensation network to optimize performance.
Stability should then be checked across all operating conditions, including load current, input voltage and temperature. The LTC1375 data sheet contains a more thorough
discussion of loop compensation and describes how to
test the stability using a transient load. Figure 5 shows
the transient response when the load current is stepped
from 500mA to 1500mA and back to 500mA.
Low Ripple Burst Mode Operation and
Pulse-Skipping Mode
The LTC4090/LTC4090-5 are capable of operating in
either low ripple Burst Mode operation or pulse-skipping
mode which are selected using the SYNC pin. Tie the
SYNC pin below VSYNC,L (typically 0.5V) for low ripple
Burst Mode operation or above VSYNC,H (typically 0.8V)
for pulse-skipping mode.
To enhance efficiency at light loads, the LTC4090/
LTC4090‑5 can be operated in low ripple Burst Mode
operation which keeps the output capacitor charged to
the proper voltage while minimizing the input quiescent
current. During Burst Mode operation, the LTC4090/
LTC4090-5 deliver single cycle bursts of current to the
output capacitor followed by sleep periods where the output power is delivered to the load by the output capacitor.
Because the LTC4090/LTC4090-5 deliver power to output
with single, low current pulses, the output ripple is kept
below 15mV for a typical application. As the load current
decreases towards a no load condition, the percentage
of time that the high voltage regulator operates in sleep
mode increases and the average input current is greatly
reduced resulting in high efficiency even at very low loads.
See Figure 6.
At higher output loads (above 70mA for the front page
application) the LTC4090/LTC4090-5 will be running at
the frequency programmed by the RT resistor, and will be
operating in standard PWM mode. The transition between
PWM and low ripple Burst Mode operation is seamless,
and will not disturb the output voltage.
VIN = 12V; FIGURE 12 SCHEMATIC
ILOAD = 10mA
FIGURE 12 SCHEMATIC
HVOUT
50mV/DIV
IL
0.5A/DIV
IL
1A/DIV
VSW
5V/DIV
25µs/DIV
VOUT
10mV/DIV
4090 F05
Figure 5. Transient Load Response of the LTC4090 High
Voltage Regulator Front Page Application as the Load
Current is Stepped from 500mA to 1500mA.
5µs/DIV
4090 F06
Figure 6. High Voltage Regulator Burst Mode Operation
4090fe
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21
LTC4090/LTC4090-5
APPLICATIONS INFORMATION
If low quiescent current is not required, the LTC4090/
LTC4090-5 can operate in pulse-skipping mode. The benefit
of this mode is that the LTC4090/LTC4090-5 will enter full
frequency standard PWM operation at a lower output load
current than when in Burst Mode operation. The front page
application circuit will switch at full frequency at output
loads higher than about 60mA.
Boost Pin Considerations
Capacitor C2 (see Block Diagram) and an internal diode
are used to generate a boost voltage that is higher than
the input voltage. In most cases, a 0.47µF capacitor will
work well. The BOOST pin must be at least 2.3V above
the SW pin for proper operation.
High Voltage Regulator Soft-Start
The HVEN pin can be used to soft-start the high voltage
regulator of the LTC4090/LTC4090-5, reducing maximum
input current during start-up. The HVEN pin is driven
through an external RC filter to create a voltage ramp at
this pin. Figure 7 shows the start-up and shutdown waveforms with the soft-start circuit. By choosing a large RC
time constant, the peak start-up current can be reduced
to the current that is required to regulate the output, with
no overshoot. Choose the value of the resistor so that it
can supply 20µA when the HVEN pin reaches 2.3V.
Synchronization and Mode
The SYNC pin allows the high voltage regulator to be
synchronized to an external clock.
IL
1A/DIV
RUN
15k
HVEN
HVEN
2V/DIV
GND
0.22µF
VOUT
2V/DIV
2ms/DIV
4090 F07
Figure 7. To Soft-Start the High Voltage Regulator,
Add a Resistor and Capacitor to the HVEN Pin
22
Synchronizing the LTC4090/LTC4090-5 internal oscillator
to an external frequency can be done by connecting a
square wave (with 20% to 80% duty cycle) to the SYNC
pin. The square wave amplitude should be such that the
valleys are below 0.3V and the peaks are above 0.8V (up
to 6V). The high voltage regulator may be synchronized
over a 300kHz to 2MHz range. The RT resistor should be
chosen such that the LTC4090/LTC4090-5 oscillate 25%
lower than the external synchronization frequency to ensure
adequate slope compensation. While synchronized, the
high voltage regulator will turn on the power switch on
positive going edges of the clock. When the power good
(PG) output is low, such as during start-up, short-circuit,
and overload conditions, the LTC4090/LTC4090-5 will
disable the synchronization feature. The SYNC pin should
be grounded when synchronization is not required.
Alternate NTC Thermistors and Biasing
The LTC4090/LTC4090-5 provide temperature qualified
charging if a grounded thermistor and a bias resistor are
connected to NTC (see Figure 8). By using a bias resistor
whose value is equal to the room temperature resistance
of the thermistor (R25C) the upper and lower temperatures
are preprogrammed to approximately 50°C and 0°C, respectively (assuming a Vishay curve 2 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.
NTC thermistors have temperature characteristics which
are indicated on resistance-temperature conversion tables.
The Vishay-Dale thermistor NTHS0603N02N1002J, used
in the following examples, has a nominal value of 10k and
follows the Vishay curve 2 resistance-temperature characteristic. The LTC4090/LTC4090-5’s trip points are designed
4090fe
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LTC4090/LTC4090-5
APPLICATIONS INFORMATION
to work with thermistors whose resistance-temperature
characteristics follow Vishay Dale’s R-T curve 2. The Vishay
NTHS0603N02N1002J is an example of such a thermistor.
However, Vishay Dale has many thermistor products that
follow the R-T curve 2 characteristic in a variety of sizes.
Furthermore, any thermistor whose ratio of rCOLD to rHOT
is about 7.0 will also work (Vishay Dale R-T curve 2 shows
a ratio of 2.815/0.409 = 6.89).
In the explanation below, the following notation is used.
R25C = Value of the Thermistor at 25°C
Solving these equations for RNTC|COLD and RNTC|HOT results
in the following:
RNTC|COLD = Value of Thermistor at the Cold Trip Point
RNTC|HOT = Value of the Thermistor at the Hot Trip Point
Therefore, the hot trip point is set when:
RNTC|HOT
RNOM + RNTC|HOT
• VNTC = 0.29 • VNTC
and the cold trip point is set when:
RNTC|COLD
RNOM + RNTC|COLD
• VNTC = 0.74 • VNTC
RNTC|HOT = 0.409 • RNOM
and
rCOLD = Ratio of RNTC|COLD to R25C
RNTC|COLD = 2.815 • RNOM
rHOT= Ratio of RNTC|HOT to R25C
By setting RNOM equal to R25C, the above equations result
in rHOT = 0.409 and rCOLD = 2.815. Referencing these ratios
to the Vishay Resistance-Temperature curve 2 chart gives
a hot trip point of about 50°C and a cold trip point of about
0°C. The difference between the hot and cold trip points
is approximately 50°C.
RNOM = Primary Thermistor Bias Resistor (see Figure 8)
R1 = Optional Temperature Range Adjustment resistor
(see Figure 9)
The trip points for the LTC4090/LTC4090-5’s temperature
qualification are internally programmed at 0.29 • VNTC for
the hot threshold and 0.74 • VNTC for the cold threshold.
VNTC
NTC BLOCK
VNTC
6
RNOM
10k
NTC
By using a bias resistor, RNOM, different in value from
R25C, 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
NTC BLOCK
6
0.738 • VNTC
–
TOO_COLD
5
+
RNTC
10k
–
0.29 • VNTC
RNOM
13.2k
NTC
0.738 • VNTC
TOO_COLD
5
+
R1
1.97k
–
TOO_HOT
0.29 • VNTC
+
–
RNTC
10k
+
TOO_HOT
+
+
NTC_ENABLE
0.1V
NTC_ENABLE
–
0.1V
4090 F08
Figure 8. Typical NTC Thermistor Circuit
–
4090 F09
Figure 9. NTC Thermistor Circuit with Additional Bias Resistor
4090fe
For more information www.linear.com/LTC4090
23
LTC4090/LTC4090-5
APPLICATIONS INFORMATION
equations can be used to easily calculate a new value for
the bias resistor:
rHOT
• R 25C
0.409
r
= COLD • R 25C
2.815
RNOM =
RNOM
In general, if the LTC4090/LTC4090-5 is being powered
from IN the power dissipation can be calculated as follows:
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 chosen, the other is determined by the default ratios
designed in the IC. Consider an example where a 40°C
hot trip point is desired.
From the Vishay curve 2 R-T characteristics, rHOT is 0.5758
at 40°C. Using the above equation, RNOM should be set to
14.0k. With this value of RNOM, the cold trip point is about
–7°C. Notice that the span is now 47°C rather than the
previous 50°C. This is due to the increase in temperature
gain of the thermistor as absolute temperature decreases.
The upper and lower temperature trip points can be independently programmed by using an additional bias resistor
as shown in Figure 9. The following formulas can be used
to compute the values of RNOM and R1:
r
–r
RNOM = COLD HOT • R 25C
2.815
R1= 0.409 • RNOM – rHOT • R 25C
For example, to set the trip points to –5°C and 55°C with
a Vishay curve 2 thermistor choose
RNOM =
3.532 – 0.3467
• 10k = 13.2k
2.815 – 0.409
the nearest 1% value is 13.3k.
R1 = 0.409 • 13.3k – 0.3467 • 10k = 1.97k
the nearest 1% value is 1.96k. The final solution is shown
in Figure 9 and results in an upper trip point of 55°C and
a lower trip point of –5°C.
Power Dissipation and High Temperature Considerations
The die temperature of the LTC4090/LTC4090-5 must be
lower than the maximum rating of 110°C. This is generally
24
not a concern unless the ambient temperature is above
85°C. The total power dissipated inside the LTC4090/
LTC4090-5 depend on many factors, including input
voltage (IN or HVIN), battery voltage, programmed charge
current, programmed input current limit, and load current.
PD = (VIN – VBAT) • IBAT + (VIN – VOUT) • IOUT
where PD is the power dissipated, IBAT is the battery charge
current, and IOUT is the application load current. For a
typical application, an example of this calculation would be:
PD = (5V – 3.7V) • 0.4A + (5V – 4.75V) • 0.1A
= 545mW
This examples assumes VIN = 5V, VOUT = 4.75V, VBAT =
3.7V, IBAT = 400mA, and IOUT = 100mA resulting in slightly
more than 0.5W total dissipation.
If the LTC4090 is being powered from HVIN, the power
dissipation can be estimated by calculating the regulator
power loss from an efficiency measurement, and subtracting the catch diode loss.
PD = (1− h) • [ VHVOUT • (IBAT +IOUT )]
V
−VD • 1− HVOUT • (IBAT +IOUT ) + 0.3V •IBAT )
VHVIN
where h is the efficiency of the high voltage regulator and
VD is the forward voltage of the catch diode at I = IBAT
+ IOUT. The first term corresponds to the power lost in
converting VHVIN to VHVOUT, the second term subtracts
the catch diode loss, and the third term is the power dissipated in the battery charger. For a typical application,
an example of this calculation would be:
PD = (1− 0.87) • [ 4V • (1A + 0.6A)]
4V
−0.4V • 1−
• (1A + 0.6A ) + 0.3V • 1A = 0.7W
12V
This example assumes 87% efficiency, VHVIN = 12V, VBAT =
3.7V (VHVOUT is about 4V), IBAT = 1A, IOUT = 600mA resulting
in about 0.7W total dissipation. If the LTC4090-5 is being
powered from HVIN, the power dissipation can be estimated
4090fe
For more information www.linear.com/LTC4090
LTC4090/LTC4090-5
APPLICATIONS INFORMATION
by calculating the regulator power loss from an efficiency
measurement, and subtracting the catch diode loss.
5V
•
PD = (1– h) • ( 5V • (IBAT +IOUT ) ) – VD • 1–
VHVIN
(IBAT +IOUT ) + ( 5V – VBAT ) •IBAT
The difference between this equation and that for the
LTC4090 is the last term, which represents the power
dissipation in the battery charger. For a typical application,
an example of this calculation would be:
5V
PD = (1– 0.87 ) • ( 5V • (1A + 0.6A ) ) – 0.4V • 1–
•
12V
(1A + 0.6A ) + ( 5V – 3.7V ) • 1A = 1.97W
Like the LTC4090 example, this examples assumes 87%
efficiency, VHVIN = 12V, VBAT = 3.7V, IBAT = 1A and IOUT
= 600mA resulting in about 2W total power dissipation.
It is important to solder the exposed backside of the package to a ground plane. This ground should be tied to other
copper layers below with thermal vias; these layers will
spread the heat dissipated by the LTC4090/LTC4090-5.
Additional vias should be placed near the catch diode.
Adding more copper to the top and bottom layers and
tying this copper to the internal planes with vias can
C1 AND D1
GND PADS
SIDE-BY-SIDE
AND SEPERATED
WITH C3 GND PAD
reduce thermal resistance further. With these steps, the
thermal resistance from die (i.e., junction) to ambient can
be reduced to qJA = 40°C/W.
Board Layout Considerations
As discussed in the previous section, it is critical that
the exposed metal pad on the backside of the LTC4090/
LTC4090-5 package be soldered to the PC board ground.
Furthermore, proper operation and minimum EMI requires
a careful printed circuit board (PCB) layout. Note that large,
switched currents flow in the power switch (between the
HVIN and SW pins), the catch diode and the HVIN input
capacitor. These components, along with the inductor and
output capacitor, should be placed on the same side of
the circuit board, and their connections should be made
on that layer. Place a local, unbroken ground plane below
these components. The loop formed by these components
should be as small as possible.
Additionally, the SW and BOOST nodes should be kept
as small as possible. Figure 10 shows the recommended
component placement with trace and via locations.
High frequency currents, such as the high voltage input
current of the LTC4090/LTC4090-5, tend to find their way
along the ground plane on a mirror path directly beneath
the incident path on the top of the board. If there are slits
or cuts in the ground plane due to other traces on that
layer, the current will be forced to go around the slits.
If high frequency currents are not allowed to flow back
through their natural least-area path, excessive voltage will
build up and radiated emissions will occur. See Figure 11.
MINIMIZE D1, L1,
C3, U1, SW PIN LOOP
U1 THERMAL PAD
SOLDERED TO PCB.
VIAS CONNECTED TO ALL
GND PLANES WITHOUT
THERMAL RELIEF
4090 F11
MINIMIZE TRACE LENGTH
4090 F10
Figure 10. Suggested Board Layout
Figure 11. Ground Currents Follow Their Incident
Path at High Speed. Slices in the Ground Plane
Cause High Voltage and Increased Emissions.
4090fe
For more information www.linear.com/LTC4090
25
LTC4090/LTC4090-5
APPLICATIONS INFORMATION
IN and HVIN Bypass Capacitor
Battery Charger Stability Considerations
Many types of capacitors can be used for input bypassing;
however, caution must be exercised when using multilayer
ceramic capacitors. Because of the self-resonant and high
Q characteristics of some types of ceramic capacitors,
high voltage transients can be generated under some
start-up conditions, such as from connecting the charger
input to a hot power source. For more information, refer
to Application Note 88.
The constant-voltage mode feedback 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 4.7µF
capacitor with a 0.2W to 1W series resistor to GND is
recommended at the BAT pin to keep ripple voltage low
when the battery is disconnected.
TYPICAL APPLICATIONS
HIGH
(7.5V TO 36V)
VOLTAGE
INPUT
HVIN
C1
1µF
50V
1206
BOOST
SW
L1
6.8µH
0.47µF
16V
C3
22µF
6.3V
1206
D1
HVEN
IN
USB
680Ω
4.7µF
6.3V
59k
1%
HPWR
LTC4090
HVOUT
VC
270pF
SUSP
0.1µF
2.1k
1%
71.5k
1%
40.2k
1%
TIMER
HVPR
Q1
1k
LOAD
OUT
4.7µF
6.3V
CLPROG
GATE
Q2
PROG
RT
PG
SYNC
BAT
VNTC
+
10k
1%
Li-Ion
BATTERY
NTC
T 10k
D: DIODES INC. B360A
L: SUMIDA CDR6D28MN-GR5
Q1, Q2: SILICONIX Si2333DS
CHRG
680Ω
4090 F12
Figure 12. 800kHz Switching Frequency
26
4090fe
For more information www.linear.com/LTC4090
LTC4090/LTC4090-5
TYPICAL APPLICATIONS
L
10µH
0.47µF
HIGH (7.5V TO 36V)
TRANSIENT TO 60V*
SW
BOOST
HVIN
4.7µF
1µF
HVOUT
IN
USB
35k
88.7k
Q1
HVPR
LTC4090
4.7µF
1k
VC
OUT
RT
BAT
TIMER
330pF
CLPROG
0.1µF
GND
2.1k
LOAD
4.7µF
PROG
71.5k
+
Li-Ion BATTERY
L: SUMIDA CDRH8D28/HP-100
* USE SCHOTTKY DIODE RATED AT VR > 45V
4090 TAO3
Figure 13. 400kHz Switching Frequency
L
2.2µH
0.47µF
HIGH (7.5V TO 16V)
VOLTAGE INPUT
SW
BOOST
HVIN
22µF
1µF
HVOUT
IN
USB
1k
VC
30k
11.5k
Q1
HVPR
LTC4090
4.7µF
RT
TIMER
330pF
0.1µF
CLPROG
2.1k
GND
OUT
BAT
PROG
71.5k
LOAD
4.7µF
+
Li-Ion BATTERY
L: SUMIDA CDRH4D22/HP-2R2
4090 TAO4
Figure 14. 2MHz Switching Frequency
4090fe
For more information www.linear.com/LTC4090
27
LTC4090/LTC4090-5
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/LTC4090#packaging for the most recent package drawings.
DJC Package
22-Lead Plastic DFN (6mm × 3mm)
(Reference LTC DWG # 05-08-1714 Rev Ø)
0.889
0.70 ±0.05
R = 0.10
0.889
3.60 ±0.05
1.65 ±0.05
2.20 ±0.05 (2 SIDES)
PACKAGE
OUTLINE
0.25 ±0.05
0.50 BSC
5.35 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. APPLY SOLDER MASK TO AREAS THAT
ARE NOT SOLDERED
3. DRAWING IS NOT TO SCALE
6.00 ±0.10
(2 SIDES)
0.889
R = 0.10
TYP
PIN 1
TOP MARK
(NOTE 6)
3.00 ±0.10
(2 SIDES)
R = 0.115
TYP
12
22
0.889
1.65 ±0.10
(2 SIDES)
11
0.200 REF
0.40 ±0.05
0.75 ±0.05
0.00 – 0.05
5.35 ±0.10
(2 SIDES)
0.25 ±0.05
0.50 BSC
1
PIN #1 NOTCH
R0.30 TYP OR
0.25mm × 45°
CHAMFER
(DJC) DFN 0605
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WXXX)
IN JEDEC PACKAGE OUTLINE M0-229
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 TOP AND BOTTOM OF PACKAGE
28
4090fe
For more information www.linear.com/LTC4090
LTC4090/LTC4090-5
REVISION HISTORY
REV
DATE
DESCRIPTION
D
03/15
Corrected comparator hookup on block diagram
PAGE NUMBER
11
E
07/17
Removed Temp Dot from IVNTC
5
4090fe
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
its circuits
as described
herein will not infringe on existing patent rights.
Forof more
information
www.linear.com/LTC4090
29
LTC4090/LTC4090-5
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