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PDF LT1769 Data sheet ( Hoja de datos )
| Número de pieza | LT1769 | |
| Descripción | Constant-Current/ Constant-Voltage 2A Battery Charger with Input Current Limiting | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1769
Constant-Current/
Constant-Voltage 2A Battery
Charger with Input Current Limiting
FEATURES
s Simple Solution to Charge NiCd, NiMH and Lithium
Rechargeable Batteries—Charging Current
Programmed by Resistors or DAC
s Adapter Current Limit Allows Maximum Possible
Charging Current During System Use*
s Precision 0.5% Accuracy for Voltage Mode Charging
s High Efficiency Current Mode PWM with 3A Internal
Switch
s 5% Charge Current Accuracy
s Adjustable Undervoltage Lockout
s Automatic Shutdown When AC Adapter is Removed
s Low Reverse Battery Drain Current: 3µA
s Current Sensing Can Be at Either Terminal of the Battery
s Charging Current Soft Start
s Shutdown Control
s Available in 28-Lead Narrow SSOP Package
U
APPLICATIO S
s Chargers for NiCd, NiMH, Lead-Acid, Lithium
Rechargeable Batteries
s Switching Regulators with Precision Current Limit
, LTC and LT are registered trademarks of Linear Technology Corporation.
*US patent number 5,723,970
**See LT1510 for 1.5A charger; see LT1511 for 3A charger
DESCRIPTIO
The LT®1769 current mode PWM battery charger is a
simple, efficient solution to fast charge modern recharge-
able batteries including lithium-ion (Li-Ion), nickel-metal-
hydride (NiMH) and nickel-cadmium (NiCd) that require
constant-current and/or constant-voltage charging. The
internal switch is capable of delivering 2A** DC current
(3A peak current). Charge current can be programmed by
resistors or a DAC to within 5%. With 0.5% reference voltage
accuracy, the LT1769 meets the critical constant-voltage
charging requirement for Li-Ion cells.
A third control loop is provided to regulate the current
drawn from the input AC adapter. This allows simulta-
neous operation of the equipment and battery charging
without overloading the adapter. Charge current is reduced
to keep the adapter current below specified levels.
The LT1769 can charge batteries ranging from 1V to 20V.
Ground sensing of current is not required and the battery’s
negative terminal can be tied directly to ground. A saturat-
ing switch running at 200kHz gives high charging effi-
ciency and small inductor size. A blocking diode is not
required between the chip and the battery because the
chip goes into sleep mode and drains only 3µA when the
wall adapter is unplugged.
TYPICAL APPLICATIO
D1††
SS24
L1**
22µH
D2
1N4148
C2
0.47µF
2nF
10k
NOTE: COMPLETE LITHIUM-ION CHARGER,
NO TERMINATION REQUIRED. RS4, R7
AND C1 ARE OPTIONAL FOR IIN LIMITING
*TOKIN OR UNITED CHEMI-CON/MARCON
CERAMIC SURFACE MOUNT
**22µH SUMIDA CDRH125
†SEE APPLICATIONS INFORMATION FOR
INPUT CURRENT LIMIT AND UNDERVOLTAGE LOCKOUT
††GENERAL SEMICONDUCTOR. FOR TJ LESS THEN 100°C
MBRS130LT3 CAN BE USED
GND CLP
SW
BOOST
LT1769
COMP1
CLN
VCC
UV
SPIN
PROG
VC
OVP SENSE BAT
RS3
200Ω
1%
RS2
200Ω
1%
RS1
0.05Ω
BATTERY CURRENT
SENSE
CIN*
15µF
R7†
500Ω
C1
1µF
0.33µF
300Ω
CPROG
1µF
R3 +
390k
0.25%
BATTERY
VOLTAGE SENSE
R4
162k
0.25%
COUT
22µF
TANT
D3††
SS24
RS4†
ADAPTER
CURRENT SENSE
VIN (ADAPTER INPUT)
11V TO 28V
TO MAIN
R5† SYSTEM LOAD
UNDERVOLTAGE
LOCKOUT
RPROG
4.93k
1%
R6
5k
8.4V
Li-Ion
VBAT
1511 • F01
Figure 1. 2A Lithium-Ion Battery Charger
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1769
VREF Line Regulation
0.003
0.002
0.001
0
ALL TEMPERATURES
–0.001
–0.002
–0.003
0
5 10 15 20 25 30
VCC (V)
1769 G04
Maximum Duty Cycle
98
97
96
95
94
93
92
91
90
0 20 40 60 80 100 120 140
JUNCTION TEMPERATURE (°C)
1769 G06
PROG Pin Characteristics
6
TJ = 125°C
TJ = 25°C
0
–6
0 1234 5
VPROG (V)
1769 G08
IVA vs ∆VOVP (Voltage Amplifier)
4
3
2
TJ = 125°C
1
TJ = 25°C
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
IVA (mA)
1769 G05
VC Pin Characteristics
–1.20
–1.08
–0.96
–0.84
–0.72
–0.60
–0.48
–0.36
–0.24
–0.12
0
0.12
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
VC (V)
1769 G07
Reference Voltage
vs Temperature
2.470
2.468
2.466
2.464
2.462
2.460
2.458
0
25 50 75 100 125 150
JUNCTION TEMPERATURE
1769 G09
5
5 Page 
LT1769
APPLICATIONS INFORMATION
LT1769
PROG
300Ω
5V
0V
PWM
IBAT = (DC)(2A)
RPROG
4.7k
Q1
VN2222
CPROG
1µF
1769 F03
Figure 3. PWM Current Programming
Lithium-Ion Charging
The 2A Lithium-Ion Battery Charger (Figure 1) charges at
a constant 2A until battery voltage reaches a limit set by R3
and R4. The charger will then automatically go into a
constant-voltage mode with current decreasing to near
zero over time as the battery reaches full charge. This is the
normal regimen for lithium-ion charging, with the charger
holding the battery at “float” voltage indefinitely. In this
case no external sensing of full charge is needed.
Battery Voltage Sense Resistors Selection
To minimize battery drain when the charger is off, current
through the R3/R4 divider is set at 15µA. The input current
to the OVP pin is 3nA and the error can be neglected.
With divider current set at 15µA, VBAT = 8.4V, R4 =
2.465/15µA = 162k and,
R3 = (R4)(VBAT − 2.465) = 162k(8.4 − 2.465)
2.465
2.465
= 390k
Li-Ion batteries typically require float voltage accuracy of
1% to 2%. Accuracy of the LT1769 OVP voltage is ±0.5%
at 25°C and ±1% over full temperature. This leads to the
possibility that very accurate (0.1%) resistors might be
needed for R3 and R4. Actually, the temperature of the
LT1769 will rarely exceed 50°C in float mode because
charging currents have tapered off to a low level, so 0.25%
resistors will normally provide the required level of overall
accuracy.
When power is on, there is about 200µA of current flowing
out of the BAT and SENSE pins. If the battery is removed
during charging, and total load including R3 and R4 is less
than 200µA, VBAT could float up to VCC even though the
loop has turned switching off. To keep VBAT regulated to
the battery voltage in this condition, R3 and R4 can be
chosen to draw 0.5mA and Q3 can be added to disconnect
them when power is off (Figure 4). R5 isolates the OVP pin
from any high frequency noise on VIN. An alternative method
is to use a Zener diode with a breakdown voltage two or three
volts higher than battery voltage to clamp the VBAT voltage.
R3
12k
0.25%
+ VBAT
8.4V
LT1769
OVP
Q3
VN2222
R5
220k
R4
4.99k
0.25%
VIN
1769 F04
Figure 4. Disconnecting Voltage Divider
Some battery manufacturers recommend terminating the
constant-voltage float mode after charge current has
dropped below a specified level (typically around 10% of
the full current) and a further time out period of 30 to 90
minutes has elapsed. This may extend battery life, so
check with the manufacturer for details. The circuit in
Figure 5 will detect when charge current has dropped
below 270mA. This logic signal is used to initiate a timeout
period, after which the LT1769 can be shut down by
pulling the VC pin low with an open collector or drain.
Some external means must be used to detect the need for
additional charging or the charger may be turned on
periodically to complete a short float-voltage cycle.
Current trip level is determined by the battery voltage, R1
through R3 and the sense resistor (RS1). D2 generates
hysteresis in the trip level to avoid multiple comparator
transitions.
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1769.PDF ] | |
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