LINER LTC1734LES6-4.2 Lithium-ion linear battery charger in thinsot Datasheet

LTC1734L
Lithium-Ion Linear
Battery Charger in ThinSOT
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FEATURES
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DESCRIPTIO
Low Profile (1mm) ThinSOTTM Package
Programmable Charge Current: 50mA to 180mA
No Blocking Diode Required
No Sense Resistor Required
1% Accurate Preset Voltage: 4.2V
Charge Current Monitor Output
for Charge Termination
Automatic Sleep Mode with Input Supply Removal
Manual Shutdown
Negligible Battery Drain Current in Shutdown
Undervoltage Lockout
Self Protection for Overcurrent/Overtemperature
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APPLICATIO S
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The LTC®1734L is a low cost, single cell, constant-current/
constant-voltage Li-Ion battery charger controller. When
combined with a few external components, the SOT-23
package forms a very small, low cost charger for single cell
lithium-ion batteries. The LTC1734L is a lower charge
current version of the LTC1734.
The LTC1734L provides a fixed float voltage of 4.2V with
1% accuracy (for 4.1V and 4.15V float voltages, contact
LTC Marketing). Constant current is programmed using a
single external resistor between the PROG pin and ground.
Manual shutdown is accomplished by floating the program resistor while removing input power automatically
puts the LTC1734L into a sleep mode. Both the shutdown
and sleep modes drain near zero current from the battery.
Charge current can be monitored via the voltage on the
PROG pin allowing a microcontroller or ADC to read the
current and determine when to terminate the charge cycle.
The output driver is both current limited and thermally
protected to prevent the LTC1734L from operating outside
of safe limits. No external blocking diode is required.
Cellular Telephones
Handheld Computers
Digital Cameras
Charging Docks and Cradles
Low Cost and Small Size Chargers
Programmable Current Sources
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
The LTC1734L can also function as a general purpose
current source or as a current source for charging nickelcadmium (NiCd) and nickel-metal-hydride (NiMH) batteries using external termination.
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TYPICAL APPLICATIO
PROG Pin Indicates Charge Status
5V
1µF
VCC
ISENSE
1
2
LTC1734L
6
GND
DRIVE
4
5
RPROG
4.7k
PROG
BAT
VBAT
4V
3V
UMT4403
IBAT = 80mA
10µF
+
2V
SINGLE
Li-Ion
BATTERY
VPROG (V)
3
VIN
5V
VBAT (V)
80mA Li-Ion Battery Charger
CONSTANT
CURRENT
1.5V
CONSTANT
VOLTAGE
VPROG
1V
1734 TA01
0V
CHARGING
BEGINS
CHARGING
COMPLETE
1734 TA01b
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LTC1734L
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ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
(Note 1)
Input Supply Voltage (VCC) ..........................– 0.3V to 9V
Input Voltage (BAT, PROG) ........ – 0.3V to (VCC + 0.3V)
Output Voltage (DRIVE) .............. – 0.3V to (VCC + 0.3V)
Output Current (ISENSE) ................................... – 210mA
Short-Circuit Duration (DRIVE) ...................... Indefinite
Junction Temperature .......................................... 125°C
Operating Ambient Temperature Range
(Note 2) ...............................................–40°C to 85°C
Operating Junction Temperature (Note 2) ............ 100°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
TOP VIEW
ISENSE 1
GND 2
VCC 3
LTC1734LES6-4.2
6 DRIVE
5 BAT
4 PROG
S6 PART MARKING
S6 PACKAGE
6-LEAD PLASTIC SOT-23
LTE6
TJMAX = 125°C, θJA = 230°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, unless otherwise noted specifications are at TA = 25°C. VCC = 5V, GND = 0V and VBAT is equal to the float voltage
unless otherwise noted. All current into a pin is positive and current out of a pin is negative. All voltages are referenced to GND,
unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VCC Supply
VCC
Input Supply Voltage (Note 5)
8
V
ICC
Quiescent VCC Pin Supply Current
VBAT = 5V, (Forces IDRIVE = IBAT = 0),
IPROG = 200µA,(7500Ω from PROG to GND)
●
670
1150
µA
ISHDN
VCC Pin Supply Current in Manual Shutdown
PROG Pin Open
●
450
900
µA
IBMS
Battery Drain Current in Manual Shutdown
(Note 3)
PROG Pin Open
●
–1
0
1
µA
IBSL
Battery Drain Current in Sleep Mode (Note 4)
VCC = 0V
●
–1
0
1
µA
VUVLOI
Undervoltage Lockout Exit Threshold
VCC Increasing
●
4.45
4.56
4.68
V
VUVLOD
VUVHYS
Undervoltage Lockout Entry Threshold
VCC Decreasing
●
4.30
4.41
4.53
Undervoltage Lockout Hysteresis
VCC Decreasing
●
4.55
150
V
mV
Charging Performance
VBAT
Output Float Voltage in Constant Voltage Mode
IBAT = 10mA, 4.55V ≤ VCC ≤ 8V
●
4.158
4.20
4.242
IBAT1
Output Full-Scale Current When Programmed
for 50mA in Constant Current Mode
RPROG = 7500Ω, 4.55V ≤ VCC ≤ 8V,
Pass PNP Beta > 50
●
39
50
60
mA
IBAT2
Output Full-Scale Current When Programmed
for 180mA in Constant Current Mode
RPROG = 2100Ω, 4.55V ≤ VCC ≤ 8V,
Pass PNP Beta > 50
●
160
180
200
mA
VCM1
Current Monitor Voltage on PROG Pin
IBAT = 10% of IBAT1, RPROG = 7500Ω,
4.55V ≤ VCC ≤ 8V, Pass PNP Beta > 50,
0°C ≤ TA ≤ 85°C
0.045
0.15
0.28
V
VCM2
Current Monitor Voltage on PROG Pin
IBAT = 10% of IBAT2, RPROG = 2100Ω,
4.55V ≤ VCC ≤ 8V, Pass PNP Beta > 50,
0°C ≤ TA ≤ 85°C
0.10
0.15
0.20
V
IDSINK
Drive Output Current
VDRIVE = 3.5V
●
20
V
mA
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LTC1734L
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, GND = 0V and VBAT is equal to the float voltage unless
otherwise noted. All current into a pin is positive and current out of a pin is negative. All voltages are referenced to GND, unless
otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
2.05
2.15
2.25
UNITS
Charger Manual Control
VMSDT
Manual Shutdown Threshold
VPROG Increasing
VMSHYS
Manual Shutdown Hysteresis
VPROG Decreasing from VMSDT
IPROGPU
Program Pin Pull-Up Current
VPROG = 2.5V
Drive Output Short-Circuit Current Limit
VDRIVE = VCC
●
V
90
mV
–6
–3
– 1.5
µA
35
65
130
mA
Protection
IDSHRT
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC1734LE is guaranteed to meet performance specifications
from 0°C to 70°C ambient temperature range and 0°C to 100°C junction
temperature range. Specifications over the – 40°C to 85°C operating
ambient temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3: Assumes that the external PNP pass transistor has negligible B-C
reverse-leakage current when the collector is biased at 4.2V (VBAT) and the
base is biased at 5V (VCC).
●
Note 4: Assumes that the external PNP pass transistor has negligible B-E
reverse-leakage current when the emitter is biased at 0V (VCC) and the
base is biased at 4.2V (VBAT).
Note 5: The 4.68V maximum undervoltage lockout (UVLO) exit threshold
must first be exceeded before the minimum VCC specification applies.
Short duration drops below the minimum VCC specification of several
microseconds or less are ignored by the UVLO. If manual shutdown is
entered, then VCC must be higher than the 4.68V maximum UVLO
threshold before manual shutdown can be exited. When operating near the
minimum VCC, a suitable PNP transistor with a low saturation voltage
must be used.
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TYPICAL PERFOR A CE CHARACTERISTICS
Float Voltage vs Temperature
and Supply Voltage
4.201
4.20
VCC = 8V
52
VCC = 5V
TA = 25°C
PNP = FCX589
RPROG = 2100Ω
4.200
VCC = 4.55V
4.19
–50 –25
50
25
0
75
TEMPERATURE (°C)
RPROG = 7.5k
PNP = FCX589
51
IBAT1 (mA)
IBAT = 10mA
PNP = FCX589
FLOAT VOLTAGE (V)
FLOAT VOLTAGE (V)
4.21
IBAT1 vs Temperature
and Supply Voltage
Float Voltage vs IBAT
50
VCC = 4.55V AND 8V
49
100
125
1734 G01
4.199
0
25
50
75 100
IBAT (mA)
125
150
175
1734 G02
48
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
1734 G03
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TYPICAL PERFOR A CE CHARACTERISTICS
IBAT2 vs Temperature
and Supply Voltage
IBAT1 vs VBAT
52
180
VCC = 4.55V AND 8V
170
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
VCC = 5V
TA = 25°C
RPROG = 7.5k
PNP = FCX589
50
BAT PIN MUST BE DISCONNECTED
AND GROUNDED TO FORCE
CC MODE IN THIS REGION
48
125
IBAT2 vs VBAT
190
IBAT2 (mA)
RPROG = 2.1k
PNP = FCX589
IBAT1 (mA)
IBAT2 (mA)
190
1
0
3
2
VBAT (V)
4
Program Pin Pull-Up Current vs
Temperature and Supply Voltage
3.6
3.5
1.6
VCC = 8V
TA = 25°C
1.2
3.2
VPROG (V)
IPROGPU (µA)
IPROGPU (µA)
5
VCC = 5V
TA = 25°C
RPROG = 7.5k
PNP = FCX589
1.4
3.4
VCC = 4.55V
4
Program Pin Voltage
vs Charge Current (50mA)
VCC = 8V
3.3
3
2
VBAT (V)
1734 G06
Program Pin Pull-Up Current
vs VPROG
VPROG = 2.5V
3.4
1
0
1734 G05
1734 G04
3.6
BAT PIN MUST BE DISCONNECTED
AND GROUNDED TO FORCE
CC MODE IN THIS REGION
180
170
5
VCC = 5V
TA = 25°C
RPROG = 2.1k
PNP = FCX589
3.0
1.0
0.8
0.6
3.2
0.4
0.2
2.6
50
25
75
0
TEMPERATURE (°C)
100
125
2
3
4
5
6
VPROG (V)
7
0
8
160
1.6
VCC = 5V
T = 25°C
1.4 A
RPROG = 2.1k
PNP = FCX589
1.2
VPROG (mV)
0.8
0.6
20
10
30
IBAT1 (mA)
Program Pin Voltage for IBAT2/10
vs Temperature and Supply Voltage
160
RPROG = 7.5k
PNP = FCX589
VCC = 8V
150
50
40
1734 F09
Program Pin Voltage for IBAT1/10
vs Temperature and Supply Voltage
Program Pin Voltage
vs Charge Current (180mA)
1.0
0
1635 G08
1734 G07
VPROG (mV)
3.0
–50 –25
VPROG (V)
LIMITS AT 25mV DUE TO
PROGRAMMING PIN PULL-UP
CURRENT (IPROGPU)
2.8
3.1
RPROG = 2.1k
PNP = FCX589
VCC = 8V
150
VCC = 4.55V
VCC = 4.55V
0.4
LIMITS AT 6mV DUE TO
PROGRAMMING PIN PULL-UP
CURRENT (IPROGPU)
0.2
0
0
45
90
135
180
IBAT2 (mA)
1734 G10
140
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
1734 G11
140
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
1734 G12
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LTC1734L
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PIN FUNCTIONS
ISENSE (Pin 1): Sense Node for Charge Current. Current
from VCC passes through the internal current sense resistor and reappears at ISENSE to supply current to the
external PNP emitter. The PNP collector provides charge
current to the battery.
GND (Pin 2): Ground. Provides a reference for the internal
voltage regulator and a return for all internal circuits.
When in the constant voltage mode, the LTC1734L will
precisely regulate the voltage between the BAT and GND
pins. The battery ground should connect close to the GND
pin to avoid voltage drop errors.
VCC (Pin 3): Positive Input Supply Voltage. Supplies
power to the internal control circuitry and external PNP
transistor through the internal current sense resistor. This
pin should be bypassed to ground with a capacitor in the
range of 1µF to 10µF.
PROG (Pin 4): Charge Current Programming, Charge
Current Monitor and Manual Shutdown Pin. Provides a
virtual reference voltage of 1.5V for an external resistor
(RPROG) tied between this pin and ground that programs
the battery charge current when the charger is in the
constant current mode. The typical charge current will be
250 times greater than the current through this resistor
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BLOCK DIAGRA
(IBAT = 375/RPROG). This pin also allows for the charge
current to be monitored. The voltage on this pin is proportional to the charge current where 1.5V corresponds to the
full programmed currrent. Floating this pin allows an
internal current source to pull the pin voltage above the
shutdown threshold voltage. Because this pin is in a signal
path, excessive capacitive loading can cause AC instability. See the Applications Information section for more
details.
BAT (Pin 5): Battery Voltage Sense Input. A precision
internal resistor divider sets the final float voltage on this
pin. This divider is disconnected in the manual shutdown
or sleep mode. When charging, approximately 34µA
flows into the BAT pin. To minimize float voltage errors,
avoid excessive resistance between the battery and the
BAT pin. For dynamically stable operation, this pin usually
requires a minimum bypass capacitance to ground of 5µF
to frequency compensate for the high frequency inductive
effects of the battery and wiring.
DRIVE (Pin 6): Base Drive Output for the External PNP
Pass Transistor. Provides a controlled sink current that
drives the base of the PNP. This pin has current limiting
protection for the LTC1734L.
VIN
1µF
VCC
3
IBAT/250
IBAT
60Ω
0.24Ω
ISENSE
1
VOLTAGE
REFERENCE
2.5V
UVLO
SHUTDOWN
+
–
REF
OUTPUT
DRIVER
A3
SHUTDOWN
DRIVE
6
TEMPERATURE AND
CURRENT LIMITING
IBAT
C1
2.15V
+
1.5V
+
SHUTDOWN
+
A2
–
–
BAT
2.5V
5
10µF
A1
SINGLE
Li-Ion
CELL
–
3µA
SHUTDOWN
4
PROG
2
1734 BD
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RPROG
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LTC1734L
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OPERATIO
The LTC1734L is a linear battery charger controller.
Operation can best be understood by referring to the
Block Diagram. Charging begins when VCC rises above
the UVLO (Undervoltage Lockout) threshold VUVLOI and
an external program resistor is connected between the
PROG pin and ground. When charging, the collector of the
external PNP provides the charge current. The PNP’s
emitter current flows through the ISENSE pin and through
the internal 0.24Ω current sense resistor. This current is
close in magnitude, but slightly more than the collector
current since it includes the base current. Amplifier A3,
along with the P-channel FET, will force the same voltage
that appears across the 0.24Ω resistor to appear across
the internal 60Ω resistor. The scale factor of 250:1 in
resistor values will cause the FET’s drain current to be 1/
250 of the charge current and it is this current that flows
through the PROG pin. In the constant current mode,
amplifier A2 is used to limit the charge current to the value
that is programmed by RPROG.
The PROG pin current, which is 1/250 of the charge
current, develops a voltage across the program resistor.
When this voltage reaches 1.5V, amplifier A2 begins
diverting current away from the output driver, thus limiting the charge current. This is the constant current mode.
The constant charge current is 250 • (1.5V/RPROG).
As the battery accepts charge, its voltage rises. When it
reaches the preset float voltage of 4.2V, a precisely divided
down version of this voltage (2.5V) is compared to the
2.5V internal reference voltage by amplifier A1. If the
battery voltage attempts to exceed 4.2V (2.5V at amplifier
A1’s input) the amplifier will divert current away from the
output driver thus maintaining 4.2V on the battery. This is
the constant voltage mode.
When in the constant voltage mode, the 250:1 current ratio
is still valid and the voltage on the PROG pin will indicate
the charge current as a proportion of the maximum current set by the current programming resistor. The battery
charge current is 250 • (VPROG/RPROG) amps. This feature
allows a microcontroller with an ADC to easily monitor
charge current and if desired, manually shut down the
charger at the appropriate time.
When VCC is applied, the charger can be manually shut
down by floating the otherwise grounded end of RPROG.
An internal 3µA current source pulls the PROG pin above
the 2.15V threshold of voltage comparator C1 initiating
shutdown.
For charging NiMH or NiCd batteries, the LTC1734L can
function as a constant current source by grounding the
BAT pin. This will prevent amplifier A1 from trying to limit
charge current and only A2 will control the current.
Fault conditions such as overheating of the die or excessive DRIVE pin current are monitored and limited.
When input power is removed or manual shutdown is
entered, the charger will drain only tiny leakage currents
from the battery, thus maximizing battery standby time.
With VCC removed the external PNP’s base is connected to
the battery by the charger. In manual shutdown the base
is connected to VCC by the charger.
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APPLICATIO S I FOR ATIO
Charger Operation
Charging begins when an input voltage is present that
exceeds the undervoltage lockout threshold (V UVLOI), a
Li-Ion battery is connected to the charger output and a
program resistor is connected from the PROG pin to
ground. During the first portion of the charge cycle, when
the battery voltage is below the preset float voltage, the
charger is in the constant current mode. As the battery
voltage rises and reaches the preset float voltage, the
charge current begins to decrease and the constant
voltage portion of the charge cycle begins. The charge
current will continue to decrease exponentially as the
battery approaches a fully charged condition.
Should the battery be removed during charging, a fast
built-in protection circuit will prevent the BAT pin from rising above 5V, allowing the precision constant voltage
circuit time to respond.
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LTC1734L
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APPLICATIONS INFORMATION
Manual Shutdown
Floating the program resistor allows an internal 3µA
current source (IPROGPU) to pull the PROG pin above the
2.15V shutdown threshold (VMSDT), thus shutting down
the charger. In this mode, the LTC1734L continues to
draw quiescent current from the supply (ISHDN), but only
a negligible leakage current is delivered to the battery
(IBMS).
Shutdown can also be accomplished by pulling the otherwise grounded end of the program resistor to a voltage
greater than 2.25V (VMSDTMax). Charging will cease above
1.5V, but the internal battery voltage resistor divider will
draw about 34µA from the battery until shutdown is
entered. Figure 1 illustrates a microcontroller configuration that can either float the resistor or force it to a voltage.
The voltage should be no more than 8V when high and
have an impedance to ground of less than 10% of the
program resistor value when low to prevent excessive
charge current errors. To reduce errors the program
resistor value may be adjusted to account for the impedance to ground. The programming resistor will prevent
potentially damaging currents if the PROG pin is forced
above VCC. Under this condition VCC may float, be loaded
down by other circuitry or be shorted to ground. If VCC is
not shorted to ground, the current through the resistor will
pull VCC up slightly.
Another method is to directly switch the PROG pin to a
voltage source when shutdown is desired (Caution: pulling the PROG below 1.5V with VCC applied will cause
excessive and uncontrolled charge currents). The voltage source must be capable of sourcing the resulting
current through the program resistor. This has the advantage of not adding any error to the program resistor
during normal operation. The voltage on the PROG pin
An NPN transistor or a diode can also be utilized to
implement shutdown from a voltage source. These have
the advantage of blocking current when the voltage source
goes low, thus automatically disconnecting the voltage
source for normal charging operation. Using an NPN
allows the use of a weak voltage source due to the current
gain of the transistor. For an NPN, connect the collector to
VCC, the base to the voltage source and the emitter to the
PROG pin. For a diode, connect the anode to the voltage
source and cathode to the PROG pin. An input high level
ranging from 3.3V to VCC should be adequate to enter
shutdown while a low level of 0.5V or less should allow for
normal charging operation. Use of inexpensive small
signal devices such as the 2N3904 or 1N914 is recommended to prevent excessive capacitive loading on the
PROG pin (see Stability section).
Sleep Mode
When the input supply is disconnected, the IC enters the
sleep mode. In this mode, the battery drain current (IBSL)
is a negligible leakage current, allowing the battery to remain connected to the charger for an extended period of
time without discharging the battery. The leakage current
is due to the reverse-biased B-E junction of the external
PNP transistor.
Undervoltage Lockout
RPROG
OPEN DRAIN
OR TOTEM
POLE OUTPUT
µC
must be greater than 2.25V (VMSDT(MAX)) to ensure
entering shutdown, but no more than 0.3V above VCC to
prevent damaging the LTC1734L from excessive PROG
pin current. An exception is if VCC is allowed to float with
no other circuitry loading VCC down. Then, because the
current will be low, it is allowable to have the PROG pin
shutdown voltage applied. A three-state logic driver with
sufficient pull-up current can be used to perform this
function by enabling the high impedance state to charge
or enabling the pull-up device to enter shutdown.
PROG
LTC1734L
ADC INPUT
1734 F01
Figure 1. Interfacing with a Microcontroller
Undervoltage lockout (UVLO) keeps the charger off until
the input voltage exceeds a predetermined threshold level
(VUVLOI) that is typically 4.56V. Approximately 150mV of
hysteresis is built in to prevent oscillation around the
threshold level. In undervoltage lockout, battery drain
current is very low (< 1µA).
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LTC1734L
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APPLICATIONS INFORMATION
Programming Constant Current
monitoring accuracy can degrade considerably at very
low current levels. If current monitoring is desired, a
minimum full-scale current of 50mA is recommended.
When in the constant current mode, the full-scale charge
current is programmed using a single external resistor
between the PROG pin and ground. This charge current
will be 250 times the current through the program resistor. The program resistor value is selected by dividing the
voltage forced across the resistor (1.5V) by the desired
resistor current:
Different charge currents can be programmed by various
means such as by switching in different program resistors
as shown in Figures 2 and 3. A voltage DAC connected
through a resistor to the PROG pin or a current DAC
connected in parallel with a resistor to the PROG pin can
also be used to program current (the resistor is required
with the IDAC to maintain AC stability as discussed in the
Stability section). Another means is to use a PWM output
from a microcontroller to duty cycle the charger into and
out of shutdown to create an average current (see Manual
Shutdown section for interfacing examples). Because
chargers are generally slow to respond, it can take up to
approximately 300µs for the charger to fully settle after a
shutdown is deasserted. This delay must be accounted for
unless the minimum PWM low duration is about 3ms or
more. Shutdown occurs within a few microseconds of a
shutdown command. The use of PWM can extend the
average current to less than the normal 50mA minimum
constant current.
RPROG = 375/IBAT
The LTC1734L is designed for an absolute maximum
current of 210mA. This translates to a maximum PROG pin
current of 840µA and a minimum program resistor of 1.8k.
Because the PROG pin is in a closed-loop signal path, the
pole frequency must be kept high enough to maintain
adequate AC stability by avoiding excessive capacitance
on the pin. See the Stability section for more details.
The minimum full-scale current that can be reliably programmed is approximately 10mA, which requires a program resistor of 37.4k. Limiting capacitive loading on the
program pin becomes more important when high value
program resistors are used. In addition, the current
3
VIN
5V
OPTIONAL FILTER
1k
PIN 4
0.1µF TO
0.5µF
CHARGE
CURRENT
MONITOR
(UNFILTERED)
4
3k
PROG
BAT
5
FZT549
IBAT
10µF
7.5k
Q1
2N7002
CONTROL 1
1
LTC1734L
2
6
GND
DRIVE
1µF
CHARGE
CURRENT
MONITOR
(FILTERED)
ISENSE
VCC
Q2
2N7002
CHARGE CURRENT CONTROL 1 CONTROL 2
0
LOW
LOW
50mA
LOW
HIGH
125mA
HIGH
LOW
175mA
HIGH
HIGH
SINGLE
Li-Ion
BATTERY
1734 F02
CONTROL 2
Figure 2. Logic Control Programming of Output Current to 0mA, 50mA, 125mA or 175mA
3
VIN
5V
1µF
2
4
3k
VCC
1
LTC1734L
6
GND
DRIVE
FZT549*
5
ILOAD
PROG
7.5k
Q1
2N7002
ISENSE
Q2
2N7002
BAT
LOAD
1734 F03
CURRENT CONTROL 1 CONTROL 2
0
LOW
LOW
50mA
LOW
HIGH
125mA
HIGH
LOW
175mA
HIGH
HIGH
*OBSERVE MAXIMUM TEMPERATURE
CONTROL 1
CONTROL 2
Figure 3. Programmable Current Source with Output Current of 0mA, 50mA, 125mA or 175mA
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Monitoring Charge Current
The voltage on the PROG pin indicates the charge current
as a proportion of the maximum current set by the
program resistor. The charge current is equal to 250 •
(VPROG/RPROG) amps. This feature allows a microcontroller with an ADC to easily monitor charge current and if
desired, manually shut down the charger at the appropriate time. The minimum PROG pin current is about 3µA
(IPROGPU).
Errors in the charge current monitor voltage on the PROG
pin and in the full-scale charge current are inversely
proportional to battery current and can be statistically
approximated as follows:
One Sigma Error(%) ≅ 1 + 0.08/IBAT(A)
Dynamic loads on the battery will cause transients to
appear on the PROG pin. Should they cause excessive
errors in charge current monitoring, a simple RC filter as
shown in Figure 2 can be used to filter the transients. The
filter will also quiet the PROG pin to help prevent momentary entry into the manual shutdown mode.
Because the PROG pin is in a closed-loop signal path the
pole frequency must be kept high enough to maintain
adequate AC stability. This means that the maximum
resistance and capacitance presented to the PROG pin
must be limited. See the Stability section for more details.
Constant Current Source
The LTC1734L can be used as a constant current source
by disabling the voltage control loop as shown in Figure 3.
This is done by pulling the BAT pin below the preset float
voltage of 4.2V by grounding the BAT pin. The program
resistor will determine the output current. The output
current range can be between approximately 10mA and
180mA, depending on the maximum power rating of the
external PNP pass transistor.
External PNP Transistor
The external PNP pass transistor must have adequate
beta, low saturation voltage and sufficient power dissipation capability (including any heat sinking, if required).
To provide 180mA of charge current with the minimum
available base drive of approximately 20mA requires a
PNP beta greater than 9.
With low supply voltages, the PNP saturation voltage
(VCESAT) becomes important. The VCESAT must be less
than the minimum supply voltage minus the maximum
voltage drop across the internal sense resistor and bond
wires (0.3Ω) and battery float voltage. If the PNP transistor can not achieve the low saturation voltage required,
base current will dramatically increase. This is to be
avoided for a number of reasons: output drive may reach
current limit resulting in the charger’s characteristics to
go out of specifications, excessive power dissipation may
force the IC into thermal shutdown, or the battery could
become discharged because some of the current from the
DRIVE pin could be pulled from the battery through the
forward biased collector base junction.
For example, to program a charge current of 100mA with
a minimum supply voltage of 4.75V, the minimum operating VCE is:
VCE(MIN)(V) = 4.75 – (0.1)(0.3) – 4.2 = 0.52V
The actual battery charge current (IBAT) is slightly less
than the expected charge current because the charger
senses the emitter current and the battery charge current
will be reduced by the base current. In terms of β (IC/IB),
IBAT can be calculated as follows:
IBAT(A) = 250 • IPROG[β/(β + 1)]
If β = 50, then IBAT is 2% low. If desired, the 2% loss can
be compensated for by increasing IPROG by 2%.
Another important factor to consider when choosing the
PNP pass transistor is the power handling capability. The
transistor’s data sheet will usually give the maximum rated
power dissipation at a given ambient temperature with a
power derating for elevated temperature operation. The
maximum power dissipation of the PNP when charging is:
PD(MAX)(W) = IBAT (VDD(MAX) – VBAT(MIN))
VDD(MAX) is the maximum supply voltage and VBAT(MIN) is
the minimum battery voltage when discharged.
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Table 1. PNP Pass Transistor Selection Guide
Maximum PD (W)
Mounted on Board
at TA = 25°C
Package Style
0.2
SC-70
0.2
SC-70
0.5
SOT-23
0.625
1
ZETEX Part Number
ROHM Part Number
Comments
UMT4403
Smallest Size
UMT2907A
Smallest Size
FMMT549
Low VCESAT
SOT-23
FMMT720
Very Low VCESAT, High Beta
SOT-89
FCX589 or BCX69
1.1
SOT-23-6
ZXT10P12DE6
1 to 2
SOT-89
FCX717
Very Low VCESAT, High Beta
Very Low VCESAT, High Beta, Small
2
SOT-223
FZT589
Low VCESAT
2
SOT-223
BCP69 or FZT549
0.75
FTR
2SB822
Low VCESAT
1
ATV
2SB1443
Low VCESAT
2
SOT-89
2SA1797
Low VCESAT
Once the maximum power dissipation and VCE(MIN) are
known, Table 1 can be used as a guide in selecting a
suitable PNP transistor. In the table, very low VCESAT is
less than 0.25V, low VCESAT is 0.25V to 0.5V and the others
are 0.5V to 0.8V all depending on the current required. See
the manufacturer’s data sheet for details. All of the PNP
transistors are rated to carry at least 1A continuously as
long as the power dissipation is within limits. The Stability
section addresses caution in the use of high beta PNPs.
Should overheating of the PNP transistor be a concern,
protection can be achieved with a positive temperature
coefficient (PTC) thermistor, wired in series with the
current programming resistor and thermally coupled to
the transistor. The PRF chip series from Murata has a
steep resistance increase at temperature thresholds from
85°C to 145°C making it behave somewhat like a thermostat switch. For example, the model PRF18BA471QB1RB
thermistor is 470Ω at 25°C, but abruptly increase its
resistance to 4.7k at 125°C. Below 125°C, the device
exhibits a small negative TC. The 470Ω thermistor can be
added in series with a 1.6k resistor to form the current
programming resistor for a 180mA charger. Should the
thermistor reach 125°C, the charge current will drop to
60mA and inhibit any further increase in temperature.
Stability
The LTC1734L contains two control loops: constant voltage and constant current. To maintain good AC stability in
the constant voltage mode, a capacitor of at least 4.7µF is
usually required from BAT to ground. The battery and
interconnecting wires appear inductive at high frequencies, and since these are in the feedback loop, this capacitance may be necessary to compensate for the inductance.
This capacitor need not exceed 100µF and its ESR can
range from near zero to several ohms depending on the
inductance to be compensated. In general, compensation
is optimal with a capacitance of 4.7µF to 22µF and an ESR
of 0.5Ω to 1.5Ω.
Using high beta PNP transistors (>300) and very low ESR
output capacitors (especially ceramic) reduces the phase
margin, possibly resulting in oscillation. Also, using high
value capacitors with very low ESRs will reduce the phase
margin. Adding a resistor of 0.5Ω to 1.5Ω in series with
the capacitor will restore the phase margin.
In the constant current mode, the PROG pin is in the
feedback loop, not the battery. Because of this, capacitance on this pin must be limited. Locating the program
resistor near the PROG pin and isolating the charge
current monitoring circuitry (if used) from the PROG pin
with a 1k to 10k resistor may be necessary if the capacitance is greater than that given by the following equation:
CMAX(pF) =
400k
RPROG
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Higher charge currents require lower program resistor
values which can tolerate more capacitive loading on the
PROG pin. Maximum capacitance can be as high as 50pF
for a charge current of 50mA (RPROG = 7.5k).
Figure 4 is a simple test circuit for checking stability in both
the constant current and constant voltage modes. With
input power applied and a near fully charged battery
connected to the charger, driving the PROG pin with a
pulse generator will cycle the charger in and out of the
manual shutdown mode. Referring to Figure 5, after a
short delay, the charger will enter the constant current
mode first, then if the battery voltage is near the programmed voltage of 4.2V, the constant voltage mode will
begin. The resulting waveform on the PROG pin is an
indication of stability.
The double exposure photo in Figure 5 shows the effects
of capacitance on the program pin. The middle waveform
is typical while the lower waveform indicates excessive
program pin capacitance resulting in constant current
mode instability. Although not common, ringing on the
constant voltage portion of the waveform is an indication
*
VIN
VCC
LTC1734L
1734 F06
*DRAIN-BULK DIODE OF FET
Figure 6. Low Loss Reverse Voltage Protection
VCC Bypass Capacitor
2V
Internal Protection
PROG
RPROG
3k
BAT
+
Li-Ion*
LTC1734L
20Ω TO
200Ω
2.5V
0V
f = 1kHz
1734 F04
*FULLY CHARGED CELL
Figure 4. Setup for AC Stability Testing
5V
1V
0V
2V
PROG PIN
(200pF ON PIN)
In some applications, protection from reverse voltage on
VCC is desired. If the supply voltage is high enough, a
series blocking diode can be used. In other cases, where
the voltage drop must be kept low, a P-channel FET as
shown in Figure 6 can be used.
0V
TO SCOPE
PROG PIN
(20pF ON PIN)
Reverse Input Voltage Protection
Many types of capacitors with values ranging from 1µF to
10µF located close to the LTC1734L will provide adequate
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 connecting
the charger input to a hot power source. To prevent these
transients from exceeding the absolute maximum voltage
rating, several ohms of resistance can be added in series
with the ceramic input capacitor.
10k
PULSE
GENERATOR
of instability due to any combination of extremely low ESR
values, high capacitance values of the output capacitor or
very high PNP transistor beta. To minimize the effect of the
scope probe capacitance, a 10k resistor is used to isolate
the probe from the program pin. Also, an adjustable load
resistor or current sink can be used to quickly alter the
charge current when a fully charged battery is used.
1V
0V
SHUT DELAY
DOWN
CONSTANT
CURRENT
CONSTANT
VOLTAGE
HORIZONTAL SCALE: 100µs/DIV
Figure 5. Stability Waveforms
Internal protection is provided to prevent excessive DRIVE
pin currents (IDSHRT) and excessive self-heating of the
LTC1734L during a fault condition. The faults can be
generated from a shorted DRIVE pin or from excessive
DRIVE pin current to the base of the external PNP
transistor when it’s in deep saturation from a very low
VCE. This protection is not designed to prevent overheating of the external pass transistor. Indirectly though, selfheating of the PNP thermally conducting to the LTC1734L
1734lf
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.
11
LTC1734L
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APPLICATIONS INFORMATION
and resulting in the IC’s junction temperature to rise
above 150°C, thus cutting off the base current to the PNP
transistor. This action will limit the transistor junction
temperature to a temperature well above 150°C. The
temperature depends on how well the IC and PNP are
thermally connected and on the transistor’s θJA. See the
External PNP Transistor section for information on protecting the transistor from overheating.
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PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
0.62
MAX
2.90 BSC
(NOTE 4)
0.95
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45
6 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD
FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
1.90 BSC
S6 TSOT-23 0302
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PART NUMBER
DESCRIPTION
COMMENTS
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Up to 1A Charge Current for Li-Ion, NiCd, NiMH or Lead-Acid
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LTC1730
Li-Ion Battery Pulse Charger
Minimizes Heat Dissipation, No Blocking Diode Required,
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LTC1731
Linear Constant-Current/Constant-Voltage Charger Controller Simple Charger Uses External FET. Features Preset Voltages,
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LTC1733
Standalone, Monolithic Linear Li-Ion Battery Charger
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LTC1734
200mA to 700mA Li-Ion Linear Charger in ThinSot
Pin Compatible with the LTC1734L, Higher Charge Current
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Up to 2A Charge Current for Li-Ion, NiCd, NiMH or Lead-Acid
Batteries with Input Current Limit
1734lf
12
Linear Technology Corporation
LT/TP 0802 2K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2001
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