LTC4012 datasheet(26/48 Pages) AD

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LTC4162-S

Rev B

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OPERATION

aVishayNTCS0402E3103FLTorNTHS0402N02N1002JE.

vcharge_setting, vabsorb_delta, and v_equalize_delta

control the 25°C value of vcharge_dac. At other tempera-

tures, the value of vcharge_dac is adjusted based on the

thermistor_voltage to produce the temperature profile

shown in Figure 2. In effect, the temperature profile is

shifted up or down by increasing or decreasing the value

of vcharge_setting. The absorb and equalize voltages

follow along. The slope of the temperature compensation

response is not software programmable but can be shifted

left or right by changing the thermistor bias circuit. The

default vabsorb_delta value is 21 which translates to an

absorb voltage of 2.4V/cell at 25°C. The default v_equal-

ize_delta value is 42 which translates to an equalize volt-

age of 2.6V/cell at 25°C. Temperature compensation is

active over a thermistor_voltage range of 21437 to 912

which corresponds to an approximate temperature range

of –55°C to 135°C.

Figure 2. 12V Lead-Acid Temperature Profile

−50 −25

75 100 125 150

TEMPERATURE (°C)

11.4

12.0

12.6

13.2

13.8

14.4

15.0

15.6

16.2

CC–CV

EQUALIZE

ABSORB

4162S F02

Low Power Ship Mode

The LTC4162 can reduce its already low battery-only

standby current to about 2.8µA in a special mode designed

for shipment and storage. Ship mode is armed by setting

arm_ship_mode to arm. It does not take effect, however,

until the input voltage VIN drops below approximately 1V.

Uponreturnoftheinputvoltageaboveapproximately1Vthe

LTC4162wakesfromshipmode.Thedecisiontoremainout

of ship mode is latched once the internal voltage reference

is re-biased and VIN is detected as having reached about

4.2V (vin_gt_4p2v). In ship mode, the VCC2P5 2.5V logic

LDO and the INTVCC 5V system LDO are deactivated and,

along with them, all logic and communications with the

I2C port. Consequently, no settings or state information

will persist through a ship mode cycle.

Oscillator Synchronization

The SYNC pin is available to synchronize the switching

battery charger to an external clock for optimum noise

immunity. To use the SYNC pin, use the RT pin to set

the frequency of the internal oscillator to the frequency

expected by the SYNC signal. If no signal is present at

SYNC, the internal oscillator will run normally. If a signal

within the required tolerance range appears at SYNC, the

internal oscillator will detect it and synchronize with it. To

avoid a long or short cycle, synchronization won't occur

until the internal oscillator and external signals coincide.

Therefore, synchronization may take several thousand

cycles (milliseconds) to occur. If SYNC is not used, it

should just be grounded.

Under Voltage Lockout Circuits/suspend_charger/

System Faults

Various supply monitor circuits, as well as suspend_char-

ger, can disable charging. If the voltage at VIN falls below

BATSENS+ (i.e. not vin_gt_vbat), or thermal_shutdown

(die temperature above ~150°C), no_rt resistor, not

intvcc_gt_2p8v, not vin_gt_4p2v, or a CELLS0/1 pins

cell_count_err, the LTC4162 suspends charging and

reports charger_suspended. In the absence of any of the

above fault conditions, charging is re-enabled when VIN

rises VIN_DUVLO above the BATSENS+ voltage.

LTC4162 Lead-Acid Variants

The LTC4162-SAD is fully programmable and follows

the descriptions given thus far but, for added safety, the

LTC4162-SST non-programmable version is available

which prevents writing to v_equalize_delta, max_equal-

ize_time, vabsorb_delta, max_absorb_time,vcharge_set-

ting and en_sla_temp_comp.

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