LINER LTC4064 Monolithic linear charger for back-up li-ion battery Datasheet

LTC4064
Monolithic Linear Charger
for Back-Up Li-Ion Batteries
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FEATURES
DESCRIPTIO
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The LTC4064 is a standalone linear charger optimized for
prolonging the life of 1-cell Li-ion batteries in battery backup applications. By charging to a float voltage of 4V
instead of 4.2V or 4.1V, the LTC4064 decelerates the aging
process and capacity degradation when the battery is
unused for long periods of time but must be in a ready
state.
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■
■
■
■
■
■
■
■
■
■
Preset 4V Charge Voltage with 1% Accuracy
Prolongs 4.2V Li-Ion Battery Lifetime
Automatic Recharge
Thermal Regulation Maximizes Charging Rate
without Risk of Overheating*
No MOSFET, Sense Resistor or Blocking Diode
Required
Programmable Charge Termination Timer
Thermistor Input for Temperature Qualified Charging
Programmable Charge Current with 7% Accuracy
C/10 Charge Current Detection Output
25µA Supply Current in Shutdown Mode
Charge Current Monitor Useful for Gas Gauging*
Charges Directly from USB Port
Tiny Thermally Enhanced 10-pin MSOP Package
An external capacitor programs a safety timer to terminate
the charge cycle while the charge current is set externally
with a single resistor. When the input supply is removed,
the LTC4064 automatically enters a low current sleep
mode, dropping the battery drain current to less than 3µA.
Additional safety features designed to maximize battery
lifetime and reliability include NTC temperature sensing
and low battery charge conditioning (trickle charging).
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APPLICATIO S
■
■
File Servers, RAID Systems
Storage Products
Li-Ion Battery Back-Up
, LTC and LT are registered trademarks of Linear Technology Corporation.
*US Patent No. 6522118
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■
The IC contains an on-chip power MOSFET and eliminates
the need for an external sense resistor and blocking diode.
The LTC4064 also includes C/10 detection circuitry, AC
present logic, and fault detection circuitry.
TYPICAL APPLICATIO
Standalone Back-Up Li-Ion Battery Charger
VIN = 5V
8
SHDN
2
VCC
BAT
4.7µF
9
IBAT = 1A
VFLOAT = 4V
LTC4064
4
7
PROG
TIMER
GND
0.1µF
5, 11
NTC
6
1.5k
1%
1-CELL
Li-Ion
BATTERY*
4064TA01
*AN OUTPUT CAPACITOR MAY BE REQUIRED
DEPENDING ON BATTERY LEAD LENGTH
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LTC4064
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Input Supply Voltage (VCC) ..................................... 10V
BAT ......................................................................... 10V
NTC, SHDN, TIMER, PROG ............ –0.3V to VCC + 0.3V
CHRG, FAULT, ACPR ................................ –0.3V to 10V
BAT Short-Circuit Duration .......................... Continuous
BAT Current (Note 2) ............................................. 1.3A
PROG Current (Note 2) ....................................... 1.3mA
Junction Temperature .......................................... 125°C
Operating Temperature Range (Note 3) ...–40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
TOP VIEW
CHRG
VCC
FAULT
TIMER
GND
1
2
3
4
5
11
10
9
8
7
6
ACPR
BAT
SHDN
PROG
NTC
LTC4064EMSE
MSE EXPOSED PAD PACKAGE
10-LEAD PLASTIC MSOP
MSE PART MARKING
TJMAX = 125°C, θJA = 40°C/W (Note 4)
EXPOSED PAD IS GND, (PIN 11)
MUST BE SOLDERED TO PCB
LTAHQ
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, otherwise specifications are at TA = 25°C. VCC = 5V
SYMBOL
PARAMETER
VCC
VCC Supply Voltage
CONDITIONS
ICC
VCC Supply Current
VFLOAT
VBAT Regulated Float Voltage
IBAT
Battery Pin Current
ITRIKL
VTRIKL
∆VTRIKL
Trickle Charge Trip Hysteresis Voltage
VUV
VCC Undervoltage Lockout Voltage
∆VUV
VCC Undervoltage Lockout Hysteresis
VMSD
Manual Shutdown Threshold Voltage
VASD
Automatic Shutdown Threshold Voltage (VCC - VBAT) High to Low
(VCC - VBAT) Low to High
MIN
●
Charger On; Current Mode; RPROG = 30k (Note 5)
Shutdown Mode; VSHDN = 0V
Sleep Mode VCC < VBAT or VCC ≤ 4V
TYP
MAX
UNITS
6.5
V
1
25
25
2
50
50
mA
µA
µA
4.25
●
●
●
●
3.96
4.00
4.04
V
RPROG = 3k; Current Mode
RPROG = 15k; Current Mode
Shutdown Mode; VSHDN = 0V
Sleep Mode VCC < VBAT or VCC < (VUV – ∆VUV)
●
●
465
93
500
100
±1
±1
535
107
±3
±3
mA
mA
µA
µA
Trickle Charge Current
VBAT < 2V; RPROG = 3k
●
35
50
65
mA
Trickle Charge Trip Threshold Voltage
VBAT Rising
VCC Rising
●
2.48
V
100
mV
4
4.25
200
SHDN Pin Voltage
0.6
1.3
35
70
V
mV
V
mV
mV
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LTC4064
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
VPROG
PROG Pin Voltage
RPROG = 3k, IPROG = 500µA
ICHRG
CHRG Pin Weak Pulldown Current
VCHRG = 1V
30
50
µA
VCHRG
CHRG Pin Output Low Voltage
ICHRG = 5mA
0.35
0.6
V
VACPR
ACPR Pin Output Low Voltage
IACPR = 5mA
0.35
0.6
V
VFAULT
FAULT Pin Output Low Voltage
IFAULT = 5mA
0.35
0.6
V
IC/10
End of Charge Indication Current Level
RPROG = 3k
50
56
mA
tTIMER
TIMER Accuracy
CTIMER = 0.1µF
∆VRECHRG
Recharge Threshold Voltage
VFLOAT - VRECHRG, VBAT > VTRIKL
Charge Termination Timer Expired
VNTC-HOT
NTC Pin Hot Threshold Voltage
VNTC Falling
2.5
V
VHOT-HYS
NTC Pin Hot Hysteresis Voltage
80
mV
VNTC-COLD
NTC Pin Cold Threshold Voltage
VNTC Rising
4.375
VCOLD-HYS
NTC Pin Cold Hystersis Voltage
VNTC-DIS
NTC Pin Disable Threshold Voltage
100
mV
VDIS-HYS
NTC Pin Disable Hystersis Voltage
10
mV
TLIM
Junction Temperature in
Constant-Temperature Mode
105
°C
RON
Power MOSFET “ON” Resistance
375
mΩ
1.5
15
44
●
65
100
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The Absolute Maximum BAT Current Rating of 1.3A is guaranteed
by design and current density calculations. The Absolute Maximum PROG
Current Rating is guaranteed to be 1/1000 of BAT current rating by design.
Note 3: The LTC4064 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
UNITS
V
10
80
VNTC Rising
MAX
%
135
mV
V
mV
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 4: Failure to solder the exposed backside of the package to the PC
board will result in a thermal resistance much higher than 40°C/W.
Note 5: Supply current includes PROG pin current (approximately 50µA)
but does not include any current delivered to the battery through the BAT
pin (approximately 50mA).
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LTC4064
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TYPICAL PERFOR A CE CHARACTERISTICS
Battery Regulation Voltage
vs Battery Charge Current
4.02
Battery Regulation Voltage
vs Temperature
VCC = 5V
TA = 25°C
RPROG = 3k
4.01
4.010
4.02
4.008
4.00
4.006
3.99
3.96
3.94
3.92
3.98
3.88
50 100 150 200 250 300 350 400 450 500
IBAT (mA)
4.000
3.998
3.994
VCC = 5V
RPROG = 3k
IBAT = 10mA
3.97
0
4.002
3.996
3.90
3.96
3.86
–50
3.992
3.990
0
25
50
75
TEMPERATURE (°C)
–25
100
4064 G01
4
125
TA = 25°C
200
100
700
IBAT (mA)
250
400
150
300
100
200
50
100
0
0
0.5
1
VCC (V)
1.5
2 2.5
VBAT (V)
3
3.5
4064 G04
4
30
4.04
100
4064 G06
1.20
VCC = 6V
1.15
VCC = 5.5V
1.10
15
VMSD (V)
ICC (µA)
VUV (V)
75
1.25
VCC = 6.5V
20
1.05
VCC = 4.5V
1.00
10
3.97
25
50
0
TEMPERATURE (°C)
1.30
VCC = 5.5V
4.02
3.98
–25
Manual Shutdown Threshold
Voltage vs Temperature and VCC
VSHDN = 0V
25
4.03
3.99
VCC = 5V
VBAT = 3.5V
RPROG = 1.5k
0
–50
4.5
Shutdown Supply Current
vs Temperature and VCC
4.00
THERMAL CONTROL
LOOP IN OPERATION
4064 G05
4.05
0.95
VCC = 5V
0.90
5
3.96
3.95
–50 –25
600
500
200
Undervoltage Lockout Voltage
vs Temperature
7
800
300
5.5
4.01
6.5
900
350
IBAT (mA)
IBAT (mA)
400
5.0
6
Charge Current vs Ambient
Temperature with Thermal
Regulation
400
4.5
5.5
VCC (V)
1000
VCC = 5V
TA = 25°C
RPROG = 3k
500
450
4.0
5
4064 G03
Charge Current vs Battery Voltage
550
500
0
4.5
4064 G02
Charge Current vs Input Voltage
300
VCC = 5V
TA = 25°C
RPROG = 3k
IBAT = 10mA
4.004
VBAT (V)
VBAT (V)
VBAT (V)
4.04
3.98
4.00
600
Battery Regulation Voltage
vs VCC
VCC = 4.5V
0.85
50
25
0
75
TEMPERATURE (°C)
100
125
4064 G07
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
4064 G08
0.80
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
4064 G09
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LTC4064
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TYPICAL PERFOR A CE CHARACTERISTICS
PROG Pin Voltage
vs Charge Current
1.515
1.515
1.6
VCC = 5V
TA = 25°C
RPROG = 3k
1.4
PROG Pin Voltage vs Temperature
Constant Current Mode
PROG Pin Voltage vs VCC
Constant Current Mode
VBAT = 3.5V
TA = 25°C
RPROG = 3k
1.510
VCC = 5V
VBAT = 4V
RPROG = 3k
1.510
1.505
0.8
0.6
VPROG (V)
1.505
1.0
VPROG (V)
VPROG (V)
1.2
1.500
1.500
1.495
1.495
1.490
1.490
0.4
0.2
1.485
0
0
50 100 150 200 250 300 350 400 450 500
CHARGE CURRENT (mA)
4
4.5
5
5.5
VCC (V)
6.5
6
Trickle Charge Current
vs Temperature
0.6
VCC = 5V
34 IBAT < C/10
32
VCHRG (V)
ICHRG (µA)
VCC = 5V
ICHRG = 5mA
0.4
31
30
29
0.3
0.2
28
27
8
100
0.5
33
9
75
CHRG Pin Output Low Voltage
vs Temperature
35
10
0
25
50
TEMPERATURE (°C)
4064 G12
CHRG Pin Weak Pull-Down
Current vs Temperature
VBAT = 2V
TA = 25°C
RPROG = 3k
0.1
26
50
25
0
75
TEMPERATURE (°C)
100
125
25
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
Timer Error vs Temperature
5
4
50
25
75
0
TEMPERATURE (°C)
100
125
4064 G15
Timer Error vs VCC
5
VCC = 5V
CTIMER = 0.1µF
TA = 25°C
CTIMER = 0.1µF
4
3
3
2
2
1
0
–1
–2
1
0
–1
–2
–3
–3
–4
–4
–5
–50 –25
0
–50 –25
125
4064 G14
4064 G13
tTIMER (%)
7
–50 –25
tTIMER (%)
IBAT (% OF PROGRAMMED CURRENT)
11
–25
4064 G11
4064 G10
12
1.485
–50
7
–5
50
25
0
75
TEMPERATURE (°C)
100
125
4064 G16
4
4.5
5
5.5
VCC (V)
6
6.5
7
4064 G17
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LTC4064
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PI FU CTIO S
CHRG (Pin 1): Open-Drain Charge Status Output. When
the battery is being charged, the CHRG pin is pulled low by
an internal N-channel MOSFET. When the charge current
drops to 10% of the full-scale current, the N-channel
MOSFET latches off and a 30µA current source is connected from the CHRG pin to ground. The C/10 latch can
be cleared by grounding the SHDN pin, momentarily, or
toggling VCC. When the timer runs out or the input supply
is removed, the current source is disconnected and the
CHRG pin is forced high impedance.
VCC (Pin 2): Positive Input Supply Voltage. When VCC is
within 35mV of VBAT or less than the undervoltage lockout
threshold, the LTC4064 enters sleep mode, dropping IBAT
to less than 3µA. VCC can range from 4.25V to 6.5V.
Bypass this pin with at least a 4.7µF ceramic capacitor to
ground.
FAULT (Pin 3): Open-Drain Fault Status Output. The
FAULT open-drain logic signal indicates that the charger
has timed out under trickle charge conditions or the NTC
comparator is indicating an out-of-range battery temperature condition. If VBAT is less that 2.48V, trickle charging
begins whereby the charge current drops to one tenth of
its programmed value and the timer period is reduced by
a factor of four. When one fourth of the timing period has
elapsed, if VBAT is still less than 2.48V, trickle charging
stops and the FAULT pin latches to ground. The fault can
be cleared by toggling VCC, momentarily grounding the
SHDN pin or pulling the BAT pin above 2.48V. If the NTC
comparator is indicating an out-of-range battery temperature condition, the FAULT pin will pull to ground until the
temperature returns to the acceptable range.
TIMER (Pin 4): Timer Capacitor. The timer period is set by
placing a capacitor, CTIMER, to ground. The timer period is:
Time (Hours) = (CTIMER • 3 hr)/(0.1µF)
Short the TIMER pin to ground to disable the internal timer
function.
NTC (Pin 6): Input to the NTC (Negative Temperature
Coefficient) Thermistor Temperature Monitoring Circuit.
With an external 10kΩ NTC thermistor to ground and a 1%
resistor to VCC, this pin can sense the temperature of the
battery pack and stop charging when it is out of range.
When the voltage at this pin drops below (0.5)•(VCC) at hot
temperatures or rises above (0.875)•(VCC) at cold, charging is suspended and the internal timer is frozen. The
CHRG pin output status is not affected in this hold state.
The FAULT pin will be pulled to ground, but not latched.
When the temperature returns to an acceptable range,
charging will resume and the FAULT pin is released. The
NTC feature can be disabled by grounding the NTC pin.
PROG (Pin 7): Charge Current Program and Charge Current Monitor Pin. The charge current is programmed by
connecting a resistor, RPROG to ground. When in constant-current mode, the LTC4064 servos the PROG pin
voltage to 1.5V. In all modes the voltage on the PROG pin
can be used to measure the charge current as follows:
IBAT = (VPROG/RPROG) • 1000.
SHDN (Pin 8): Shutdown Input Pin. Pulling the SHDN pin
to ground will put the LTC4064 into standby mode where
the BAT drain current is reduced to less than 3µA, and the
supply current is reduced to less than 25µA. For normal
operation, pull the SHDN pin up to VCC.
BAT (Pin 9): Charge Current Output. A bypass capacitor of
at least 1µF with a 1Ω series resistor is required to keep the
loop stable when the battery is not present. A precision
internal resistor divider sets the final float potential on this
pin. The internal resistor divider is disconnected in sleep
and shutdown mode.
ACPR (Pin 10): Open-Drain Power Supply Status Output.
When VCC is greater than the undervoltage lockout threshold and at least 35mV above VBAT, the ACPR pin will pull
to ground. Otherwise, the pin is high impedance.
GND (Pins 5, 11): Ground. The exposed backside of the
package is also ground and must be soldered to the PC
board for maximum heat transfer.
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LTC4064
W
W
SI PLIFIED BLOCK DIAGRA
VCC
2
–
105°C
D1
TA
D2
+
TDIE
M2
×1
D3
M1
×1000
+
–
MA
9
30µA
NTC 6
BAT
R1
NTC
MP
+
VA
–
CA
R2
+
–
2.485V
REF
HOT COLD DISABLE
CHRG 1
STOP
SHDN
8 SHDN
C/10
R3
30µA
1.5V
LOGIC
ACPR 10
R4
ACPR
0.15V
+
C2
C/10
FAULT 3
R5
–
FAULT
CHARGE
COUNTER
C3
OSCILLATOR
–
2.485V
4
+
TO BAT
7
TIMER
PROG
5, 11
GND
4064 BD
RPROG
CTIMER
Figure 1
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LTC4064
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OPERATIO
The LTC4064 is a linear battery charger designed primarily
for charging single cell lithium-ion batteries used in backup applications. With a 4V final float voltage accuracy of
±1%, the LTC4064 maximizes the lifetime of 4.2V chemistry lithium-ion batteries. A precision, automatic recharge
feature ensures that the battery voltage remains within
100mV of this 4V float voltage at all times.
Featuring an internal P-channel power MOSFET, the charger
uses a constant-current/constant-voltage charge algorithm with programmable current and a programmable
timer for charge termination. Charge current can be
programmed up to 1.25A with an accuracy of ±7%. No
blocking diode or sense resistor is required thus dropping
the external component count to three for the basic
charger circuit. The CHRG, ACPR, and FAULT open-drain
status outputs provide information regarding the status of
the LTC4064 at all times. An NTC thermistor input
provides the option of charge qualification using battery
temperature.
An internal thermal limit reduces the programmed charge
current if the die temperature attempts to rise above a
preset value of approximately 105°C. This feature protects
the LTC4064 from excessive temperature, and allows the
user to push the limits of the power handling capability of
a given circuit board without risk of damaging the LTC4064
or the external components. Another benefit of the LTC4064
thermal limit is that charge current can be set according to
typical, not worst-case, ambient temperatures for a given
application with the assurance that the charger will automatically reduce the current in worst-case conditions.
The charge cycle begins when the voltage at the VCC pin
rises above the UVLO level, a program resistor is connected from the PROG pin to ground, and the SHDN pin is
pulled above the shutdown threshold. At the beginning of
the charge cycle, if the battery voltage is below 2.48V, the
charger goes into trickle charge mode to bring the cell
voltage up to a safe level for charging. The charger goes
into the fast charge constant-current mode once the
voltage on the BAT pin rises above 2.48V. In constantcurrent mode, the charge current is set by RPROG.
When the battery approaches the final float voltage, the
charge current begins to decrease as the LTC4064 enters
the constant-voltage mode. When the current drops to
10% of the full-scale charge current, an internal comparator latches off the MOSFET on the CHRG pin and connects
a weak current source to ground (30µA) to indicate a near
end-of-charge (C/10) condition. The C/10 latch can be
cleared by grounding the SHDN pin momentarily, or
momentarily removing and reapplying VCC.
An external capacitor on the TIMER pin sets the total
charge time. When this time elapses, the charge cycle
terminates and the CHRG pin assumes a high impedance
state. To restart the charge cycle, remove the input voltage
and reapply it, or momentarily force the SHDN pin to 0V.
The charge cycle will also restart if the BAT pin voltage falls
below the recharge threshold.
When the input voltage is not present, the charger goes
into a sleep mode, dropping battery drain current, IBAT, to
less than 3µA. This greatly reduces the current drain on the
battery and increases the standby time. The charger can be
shut down (ICC = 25µA) by forcing the SHDN pin to 0V.
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LTC4064
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APPLICATIO S I FOR ATIO
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until VCC
rises above the undervoltage lockout threshold. The UVLO
circuit has a built-in hysteresis of 200mV. Furthermore, to
protect against reverse current in the power MOSFET, the
UVLO circuit keeps the charger in shutdown mode if VCC
falls to within 35mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown until VCC rises 70mV above the battery voltage.
For example, if 500mA charge current is required,
calculate:
RPROG = 1500V/0.5A = 3kΩ
For best stability over temperature and time, 1% metalfilm resistors are recommended.
If the charger is in constant-temperature or constantvoltage mode, the battery current can be monitored by
measuring the PROG pin voltage as follows:
IBAT = (VPROG / RPROG) • 1000
Trickle Charge And Defective Battery Detection
USB and Wall Adapter Power
At the beginning of a charge cycle, if the battery voltage is
low (below 2.48V) the charger goes into trickle charge
reducing the charge current to 10% of the full-scale
current. If the low battery voltage persists for one quarter
of the total charge time, the battery is assumed to be
defective, the charge cycle is terminated, the CHRG pin
output assumes a high impedance state, and the FAULT
pin pulls low. The fault can be cleared by toggling VCC,
temporarily forcing the SHDN pin to 0V, or temporarily
forcing the BAT pin voltage above 2.48V.
Although the LTC4064 allows charging from a USB port,
a wall adapter can also be used to charge Li-Ion batteries.
Figure 2 shows an example of how to combine wall adapter
and USB power inputs. A P-channel MOSFET, MP1, is
used to prevent back conducting into the USB port when
a wall adapter is present and Schottky diode, D1, is used
to prevent USB power loss through the 1k pull-down
resistor.
Shutdown
The LTC4064 can be shut down (ICC = 25µA) by pulling the
SHDN pin to 0V. For normal operation, pull the SHDN pin
above the manual shutdown threshold voltage level. Do
not leave this pin open. In shutdown the internal linear
regulator is turned off, and the internal timer is reset.
Programming Charge Current
Typically a wall adapter can supply significantly more
current than the 500mA-limited USB port. Therefore, an Nchannel MOSFET, MN1 and an extra 3k program resistor
can be used to increase the charge current to 1A when the
wall adapter is present.
5V WALL
ADAPTER
1A ICHG
USB
POWER
500mA ICHG
LTC4064
D1
2
MP1
BAT
= (1.5V / RPROG) • 1000 or
ICHG
SYSTEM
LOAD
VCC
The formula for the battery charge current (see Figure 1)
is:
ICHG = (IPROG) • 1000
9
PROG
7
+
Li-Ion
BATTERY
3k
1k
MN1
3k
4064 F02
RPROG = 1500V/ICHG
where RPROG is the total resistance from the PROG pin to
ground. Under trickle charge conditions, this current is
reduced to 10% of the full-scale value.
Figure 2. Combining Wall Adapter and USB Power
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LTC4064
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APPLICATIO S I FOR ATIO
Programming The Timer
The programmable timer is used to terminate the charge
cycle. The timer duration is programmed by an external
capacitor at the TIMER pin. The total charge time is:
Table 1.
FAULT
CHRG
High
Low
Charge cycle has started, C/10 has not been
reached and charging is proceeding normally.
Low
Low
Charge cycle has started, C/10 has not been
reached, but the charge current and timer
have been paused due to an NTC out-oftemperature condition.
High
30µA
pull-down
C/10 has been reached and charging is
proceeding normally.
Low
30µA
pull-down
C/10 has been reached but the charge current
and timer have paused due to an NTC out-oftemperature condition.
High
High
Normal timeout (charging has terminated).
Low
High
If FAULT goes low and CHRG goes high
impedance simultaneously, then the LTC4064
has timed out due to a bad cell (VBAT <2.48V
after one-quarter the programmed charge time).
If CHRG goes high impedance first, then
the LTC4064 has timed out normally (charging
has terminated), but NTC is indicating an outof-temperature condition.
Time (Hours) = (3 Hours) • (CTIMER/0.1µF) or
CTIMER = 0.1µF • Time (Hours)/3 (Hours)
The timer starts when an input voltage greater than the
undervoltage lockout threshold level is applied and the
SHDN pin is greater than the manual shutdown threshold
voltage level. After a time-out occurs, the charge current
stops, and the CHRG output assumes a high impedance
state to indicate that the charging has stopped. Connecting the TIMER pin to ground disables the timer function.
Recharge
After a charge cycle has terminated, if the battery voltage
drops below the recharge threshold of 3.90V a new charge
cycle will begin. The recharge circuit integrates the BAT
pin voltage for a few milliseconds to prevent a transient
from restarting the charge cycle.
If the battery voltage remains below 2.48V during trickle
charge for 1/4 of the programmed time, the battery may be
defective and the charge cycle will end. In addition, the
recharge comparator is disabled and a new charge cycle
will not begin unless the input voltage is toggled off-thenon, the SHDN pin is momentarily pulled to ground, or the
BAT pin is pulled above the 2.48V trickle charge threshold.
Open-Drain Status Outputs
The LTC4064 has three open-drain status outputs: ACPR,
CHRG and FAULT. The ACPR pin pulls low when an input
voltage greater than the undervoltage lockout threshold is
applied and becomes high impedance when power (VIN <
VUV) is removed. CHRG and FAULT work together to
indicate the status of the charge cycle. Table 1 describes
the status of the charge cycle based on the CHRG and
FAULT outputs.
Description
CHRG Status Output Pin
When the charge cycle starts, the CHRG pin is pulled to
ground by an internal N-channel MOSFET capable of
driving an LED. When the charge current drops to 10% of
the full-scale current (C/10), the N-channel MOSFET is
latched off and a weak 30µA current source to ground is
connected to the CHRG pin. After a time-out occurs,
the pin assumes a high impedance state. By using two
different value pull-up resistors a microprocessor can
detect three states from this pin (charging, C/10 and timeout). See Figure 3.
When the LTC4064 is in charge mode, the CHRG pin is
pulled low by the internal N-channel MOSFET. To detect
this mode, force the digital output pin, OUT, high and
measure the voltage at the CHRG pin. The N-channel
MOSFET will pull the pin low even with the 2k pull-up
resistor. Once the charge current drops to 10% of the
sn4064 4064fs
10
LTC4064
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APPLICATIO S I FOR ATIO
V+
VDD
VCC
7/8 VCC
8
VCC
400k
LTC4064
CHRG
3
–
RHOT
1%
2k
TOO COLD
+
µPROCESSOR
OUT
NTC
IN
4064 F03
RNTC
10k
TOO HOT
–
Figure 3. Microprocessor Interface
full-scale current (C/10), the N-channel MOSFET is turned
off and a 30µA current source is connected to the CHRG
pin. The IN pin will then be pulled high by the 2k pull-up.
By forcing the OUT pin to a high impedance state, the
current source will pull the pin low through the 400k
resistor. When the internal timer has expired, the CHRG
pin will assume a high impedance state and the 400k
resistor will then pull the pin high to indicate that charging
has terminated.
NTC Thermistor
The battery temperature is measured by placing a negative
temperature coefficient (NTC) thermistor close to the
battery pack. The NTC circuitry is shown in Figure 4. To use
this feature, connect a 10k NTC thermistor between the
NTC pin and ground and a resistor (RHOT) from the NTC pin
to VCC. RHOT should be a 1% resistor with a value equal to
the value of the chosen NTC thermistor at 50°C (this value
is 4.1k for a Vishay NTHS0603N02N1002J thermistor).
The LTC4064 goes into hold mode when the resistance of
the NTC thermistor drops below 4.1k which should be
approximately 50°C. The hold mode freezes the timer and
stops the charge cycle until the thermistor indicates a
return to a valid temperature. As the temperature drops,
the resistance of the NTC thermistor rises. The LTC4064
is designed to go into hold mode when the value of the NTC
thermistor increases to seven times the value of RHOT. For
a Vishay NTHS0603N02N1002J thermistor, this value is
28.7k which corresponds to approximately 0°C. The hot
and cold comparators each have approximately 2°C of
hysteresis to prevent oscillation about the trip point. The
NTC function can be disabled by grounding the NTC pin.
+
1/2 VCC
+
3/160 VCC
DISABLE NTC
–
LTC4064
4064 F04
Figure 4
Thermistors
The LTC4064 NTC trip points were designed 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. Futhermore, 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 RCOLD to RHOT of 2.816/0.4086 = 6.9).
NTC Layout Considerations
It is important that the NTC thermistor not be in close
thermal contact with the LTC4064. Because the LTC4064
package can reach temperatures in excess of the 50°C trip
point, the NTC function can cause a hysteretic oscillation
which turns the charge current on and off according to the
package temperature rather than the battery temperature.
This problem can be eliminated by thermally coupling the
NTC thermistor to the battery and not to the LTC4064.
Furthermore, it is essential that the VCC connection to
RHOT is made according to standard Kelvin sense techniques. Since VCC is a high current path into the LTC4064,
it is essential to minimize voltage drops between the VCC
input pin and the top of RHOT.
sn4064 4064fs
11
LTC4064
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APPLICATIO S I FOR ATIO
NTC Trip Point Errors
When a 1% resistor is used for RHOT, the major error in
the 50°C trip point is determined by the tolerance of
the NTC thermistor. A typical 10k NTC thermistor has
a ±10% tolerance. By looking up the temperature
coefficient of the thermistor at 50°C, the tolerance error
can be calculated in degrees centigrade. Consider the
Vishay NTHS0603N02N1002J thermistor which has a
temperature coefficient of –3.3%/°C at 50°C. Dividing
the tolerance by the temperature coefficient, ±10%/
(3.3%/°C) = ±3°C, gives the temperature error of the hot
trip point.
The cold trip point is a little more complicated because its
error depends on the tolerance of the NTC thermistor and
the degree to which the ratio of its value at 0°C and its value
at 50°C varies from 7 to 1. Therefore, the cold trip point
error can be calculated using the tolerance, TOL, the
temperature coefficient of the thermistor at 0°C, TC
(in %/°C), the value of the thermistor at 0°C, RCOLD, and
the value of the thermistor at 50°C, RHOT. The formula is:
⎛ 1 + TOL RCOLD ⎞
•
– 1⎟ • 100
⎜
RHOT
⎠
Temperature Error (°C) = ⎝ 7
TC
For example, the Vishay NTHS0603N02N1002J thermistor
with a tolerance of ±10%, TC of –4.5%/°C, and RCOLD/
RHOT of 6.89, has a cold trip point error of:
⎛ 1 ± 0.10
⎞
• 6.89 – 1⎟ • 100
⎜
⎠
Temperature Error (°C) = ⎝ 7
– 4.5
= –1.8°C, +2.5°C
If a thermistor with a tolerance less than ±10% is used, the
trip point errors begin to depend on errors other than
thermistor tolerance including the input offset voltage of
the internal comparators of the LTC4064 and the effects of
internal voltage drops due to high charging currents.
Constant-Current/Constant-Voltage/
Constant-Temperature
The LTC4064 uses a unique architecture to charge a
battery in a constant-current, constant-voltage, constanttemperature fashion. Figure 1 shows a simplified block
diagram of the LTC4064. Three of the amplifier feedback
loops shown control the constant-current, CA, constantvoltage, VA, and constant-temperature, TA modes. A
fourth amplifier feedback loop, MA, is used to increase the
output impedance of the current source pair, M1 and M2
(note that M1 is the internal P-channel power MOSFET). It
ensures that the drain current of M1 is exactly 1000 times
greater than the drain current of M2.
Amplifiers CA, TA, and VA are used in three separate
feedback loops to force the charger into constant-current,
temperature, or voltage mode, respectively. Diodes, D1,
D2, and D3 provide priority to whichever loop is trying to
reduce the charge current the most. The outputs of the
other two amplifiers saturate low which effectively removes their loops from the system. When in constantcurrent mode, CA servos the voltage at the PROG pin to be
precisely 1.50V (or 0.15V when in trickle-charge mode).
TA limits the die temperature to approximately 105°C
when in constant-temperature mode and the PROG pin
voltage gives an indication of the charge current as discussed in “Programming Charge Current”. VA servos its
inverting input to precisely 2.485V when in constantvoltage mode and the internal resistor divider made up of
R1 and R2 ensures that the battery voltage is maintained
at 4V. Again, the PROG pin voltage gives an indication of
the charge current.
In typical operation, the charge cycle begins in constantcurrent mode with the current delivered to the battery
equal to 1500V/RPROG. If the power dissipation of the
LTC4064 results in the junction temperature approaching
105°C, the amplifier (TA) will begin decreasing the charge
current to limit the die temperature to approximately
105°C. As the battery voltage rises, the LTC4064 either
returns to constant-current mode or it enters constantvoltage mode straight from constant-temperature mode.
sn4064 4064fs
12
LTC4064
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APPLICATIO S I FOR ATIO
Regardless of mode, the voltage at the PROG pin is
proportional to the current being delivered to the battery.
Power Dissipation
The conditions that cause the LTC4064 to reduce charge
current due to the thermal protection feedback can be
approximated by considering the power dissipated in the
IC. For high charge currents, the LTC4064 power dissipation is approximately:
PD = (VCC – VBAT) • IBAT
where PD is the power dissipated, VCC is the input supply
voltage, VBAT is the battery voltage, and IBAT is the battery
charge current. It is not necessary to perform any worstcase power dissipation scenarios because the LTC4064
will automatically reduce the charge current to maintain
the die temperature at approximately 105°C. However, the
approximate ambient temperature at which the thermal
feedback begins to protect the IC is:
TA = 105°C – PDθJA
TA = 105°C – (VCC – VBAT) • IBAT • θJA
Example: Consider an LTC4064 operating from a 5V wall
adapter providing 1.2A to a 3.75V Li-Ion battery. The
ambient temperature above which the LTC4064 will begin
to reduce the 1.2A charge current is approximately:
TA = 105°C – (5V – 3.75V) • 1.2A • 40°C/W
TA = 105°C – 1.5W • 40°C/W = 105°C – 60°C = 45°C
The LTC4064 can be used above 45°C, but the charge
current will be reduced below 1.2A. The approximate
charge current at a given ambient temperature can be
approximated by:
IBAT =
105°C – TA
(VCC – VBAT )• θ JA
Consider the above example with an ambient temperature
of 55°C. The charge current will be reduced to approximately:
IBAT =
105°C – 55°C
50°C
=
= 1A
(5V – 3.75V)• 40°C / W 50°C / A
Furthermore, the voltage at the PROG pin will change
proportionally with the charge current as discussed in the
Programming Charge Current section.
It is important to remember that LTC4064 applications do
not need to be designed for worst-case thermal conditions
since the IC will automatically reduce power dissipation
when the junction temperature reaches approximately
105°C.
Board Layout Considerations
The ability to deliver maximum charge current under all
conditions require that the exposed metal pad on the
backside of the LTC4064 package be soldered to the PC
board ground. Correctly soldered to a 2500mm2 doublesided 1oz. copper board the LTC4064 has a thermal
resistance of approximately 40°C/W. Failure to make
thermal contact between the exposed pad on the backside
of the package and the copper board will result in thermal
resistances far greater than 40°C/W. As an example, a
correctly soldered LTC4064 can deliver over 1250mA to a
battery from a 5V supply at room temperature. Without a
backside thermal connection, this number could drop to
less than 500mA.
VCC Bypass Capacitor
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 connecting the charger input
to a hot power source. For more information refer to
Application Note 88.
Stability
The constant-voltage mode feedback loop is stable
without any compensation provided that a battery is
connected. However, a 1µF capacitor with a 1Ω series
resistor to GND is recommended at the BAT pin to keep
ripple voltage low when the battery is disconnected.
In the constant-current mode it is the PROG pin that is in
the feedback loop and not the battery. The constantcurrent mode stability is affected by the impedance at the
sn4064 4064fs
13
LTC4064
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APPLICATIO S I FOR ATIO
PROG pin. With no additional capacitance on the PROG
pin, stability is acceptable with program resistor values as
high as 50k. However, additional capacitance on this node
reduces the maximum allowed program resistor. The pole
frequency at the PROG pin should be kept above 500kHz.
Therefore, if the PROG pin is loaded with a capacitance, C,
the following equation should be used to calculate the
maximum resistance value for RPROG:
RPROG < 1/(6.283 • 5 × 105 • C)
Average, rather than instantaneous, battery current may
be of interest to the user. For example, if a switching power
supply operating in low-current mode is connected in
parallel with the battery the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
filter can be used on the PROG pin to measure the average
battery current as shown in Figure 5. A 10k resistor is
added between the PROG pin and the filter capacitor and
monitoring circuit to ensure stability.
LTC4064
PROG
GND
5
CHARGE
CURRENT
MONITOR
CIRCUITRY
10k
7
RPROG
CFILTER
4064 F05
Figure 5. Isolating Capacitive Load on PROG Pin and Filtering
sn4064 4064fs
14
LTC4064
U
PACKAGE DESCRIPTIO
MSE Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1663)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.794 ± 0.102
(.110 ± .004)
5.23
(.206)
MIN
0.889 ± 0.127
(.035 ± .005)
1
2.06 ± 0.102
(.081 ± .004)
1.83 ± 0.102
(.072 ± .004)
2.083 ± 0.102 3.20 – 3.45
(.082 ± .004) (.126 – .136)
10
0.50
0.305 ± 0.038
(.0197)
(.0120 ± .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
0.254
(.010)
DETAIL “A”
0° – 6° TYP
1 2 3 4 5
GAUGE PLANE
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
0.18
(.007)
0.497 ± 0.076
(.0196 ± .003)
REF
10 9 8 7 6
SEATING
PLANE
0.86
(.034)
REF
1.10
(.043)
MAX
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.127 ± 0.076
(.005 ± .003)
MSOP (MSE) 0603
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
sn4064 4064fs
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.
15
LTC4064
U
TYPICAL APPLICATIO S
USB/Wall Adapter Power Li-Ion Battery Charger
5V WALL
ADAPTER
LTC4064
BAT
2
USB
POWER
IBAT
9
1µF
VCC
+
Li-Ion
CELL
1Ω
4.7µF
4
1k
TIMER
SHDN
8
SUSPEND
GND NTC PROG
5
7
6
µC
3.74k
0.1µF
100mA/
500mA
15k
4064 TA02
Li-Ion Battery Charger with Reverse Polarity Input Protection
2
5V WALL
ADAPTER
8
4.7µF
4
LTC4064
VCC
BAT
VIN = 5V
IBAT = 1A
1k
PROG
GND
NTC
0.1µF 5
6
8
SHDN
1k
1-CELL+
Li-Ion
BATTERY
SHDN
TIMER
9
Full Featured Single Cell Li-Ion Charger
1k
2
VCC
4k
1%
ACPR
10
1
7
4.7µF
1.5k
1%
3
CHRG
FAULT
LTC4064
6
9
NTC
BAT
4
RNTC
10k
4064 TA03
TIMER
PROG
GND
0.1µF
5
IBAT = 500mA
1µF
7
3k
1%
1Ω
Li-Ion
CELL
4064 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
LT1571
LTC1731
200kHz/500kHz Switching Battery Charger
Lithium-Ion Linear Battery Charger Controller
COMMENTS
LTC1733
LTC1734
LTC1734L
LTC4006
Up to 1.5A Charge Current; Preset and Adjustable Battery Voltages
Simple Charger uses External FET, Features Preset Voltages, C/10
Charger Detection and Programmable Timer
Lithium-Ion Linear Battery Charger Controller
Simple Charger uses External FET, Features Preset Voltages, C/10
Charger Detection and Programmable Timer, Input Power Good Indication
Monolithic Lithium-Ion Linear Battery Charger
Standalone Charger with Programmable Timer, Up to 1.5A Charge Current
Lithium-Ion Linear Battery Charger in ThinSOTTM
Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed
Lithium-Ion Linear Battery Charger Controller
50mA to 180mA, No Blocking Diode, No Sense Resistor Needed
4A Lithium-Ion Synchronous Switching Battery Charger 6V ≤ VIN ≤ 28V; 2-, 3-, 4-Cell Lithium-Ion Batteries; Up to 96% Efficiency
LTC4050
Lithium-Ion Linear Battery Charger Controller
LTC4052
Lithium-Ion Linear Battery Pulse Charger
LTC4054
Standalone Lithium-Ion Linear Battery Charger in
ThinSOT
Standalone Lithium-Ion Linear Battery Charger
Controller in ThinSOT
LTC1732
LTC4056
Simple Charger uses External FET, Thermistor Input for
Battery Temperature Sensing
Fully Integrated, Standalone Pulse Charger, Minimal Heat Dissipation,
Overcurrent Protection
Up to 800mA Charge Current, Thermal Regulation, USB Compatible,
Charge Termination
Up to 700mA Charge Current, Charge Termination, Continuous Charging
with Poorly Regulated or High Impedance Input Supplies
ThinSOT is a trademark of Linear Technology Corporation.
sn4064 4064fs
16
Linear Technology Corporation
LT/TP 0803 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2001