LTC1731EMS8-8.4#PBF Linear Technology, LTC1731EMS8-8.4#PBF Datasheet - Page 8

• Manufacturer Part Number: LTC1731EMS8-8.4#PBF
• Description: IC BATT CHRG CNTRLR LI-ION 8MSOP
• Manufacturer: Linear Technology

Specifications of LTC1731EMS8-8.4#PBF

• Function: Charge Management
• Battery Type: Li-Ion, NiCd, NiMH
• Voltage - Supply: 8.8 V ~ 12 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS
LTC1731-8.2/LTC1731-8.4
Charger Conditions
The charger is off when any of the following conditions
exist: the V
- V
timer has ended. The DRV pin will be pulled to V
internal resistor divider is disconnected to reduce the
current drain on the battery.
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until V
rises above 8.2V. To prevent oscillation around
V
Trickle Charge and Defective Battery Detection
At the beginning of the charging sequence, if the battery
voltage is less than 4.95V the charger goes into trickle
charge mode. The charge current is reduced to 10% of the
full-scale current. If the low battery voltage persists for
one quarter of the total charging time, the battery is
considered defective, charging will be terminated and the
CHRG pin output is forced to a high impedance state.
Shutdown
The LTC1731-8.2/LTC1731-8.4 can be forced into shut-
down by floating the PROG pin and allowing the internal
2.5 A current source to pull the pin above the 2.457V
shutdown threshold voltage. The DRV pin is then pulled
up to V
internal timer is reset in the shutdown mode.
Programming Charge Current
The formula for the battery charge current (see Block
Diagram) is:
where R
ground.
For example, if 0.5A charge current is needed, select a
value for R
charge current. R
8
CC
BAT
I
R
BAT
PROG
= 8.2V, the UVLO circuit has built-in hysteresis.
) is less than 54mV, the PROG pin is floating, or the
CC
= (2.457V/R
PROG
turning off the external P-channel MOSFET. The
= (2.457V/500mA)(800 /0.2 ) = 19.656k
CC
SENSE
pin is less than 8.2V, the droput voltage (V
is the total resistance from the PROG pin to
SENSE
that will drop 100mV at the maximum
U
PROG
= 0.1V/0.5A = 0.2 , then calculate:
)(800 /R
INFORMATION
U
SENSE
W
)
U
CC
and the
CC
CC
For best stability over temperature and time, 1% resistors
are recommended. The closest 1% resistor value is 19.6k.
Programming the Timer
The programmable timer is used to terminate the charge.
The length of the timer is programmed by an external
capacitor at the TIMER pin. The total charge time is:
The timer starts when the input voltage greater than 8.2V
is applied and the program resistor is connected to ground.
After a time-out occurs, the CHRG output will become high
impedance indicating that the charge cycle has ended.
Connecting the TIMER pin to V
also puts the charger into a constant-current mode. To
only disable the timer function, short the TIMER pin to
GND.
CHRG Status Output Pin
When the charge cycle starts, the CHRG pin is pulled to
ground by an internal N-channel MOSFET that can drive an
LED. When the charge current drops to 10% of the full-
scale current (C/10), the N-channel MOSFET turns off and
a weak 100 A current source to ground is connected to the
CHRG pin. After a time-out occurs, the CHRG pin goes
high impedance indicating that the charge cycle has ended.
By using two different value pull-up resistors, a micropro-
cessor can detect three states from this pin (charging,
C/10 and stop charging). See Figure 1.
Time (Hours) = (3 Hours)(C
LTC1731-8.4
Figure 1. Microprocessor Interface
V
V
CC
+
CHRG
7
2
100k
2k
TIMER
CC
disables the timer and
OUT
IN
PROCESSOR
/0.1 F)
V
DD
1731 F01
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