LTC1325CSW datasheet(13/24 Pages) LINER

13 / 24 page

LTC1325

FUNCTIONAL DESCRIPTIO

The chip enters the discharge mode when the proper

mode command bits are set and the power shutdown

command bit is clear. If a fault condition does not exist,

then the DIS pin is pulled up to VDD by the internal driver.

The DIS voltage is used to turn on an external transistor

which discharges the battery through an external series

resistor RDIS.

Discharging will continue until a new command word is

input to change the mode or a fault condition occurs.

Charge Mode

Command: MOD1 = 1, MOD0 = 0, PS = 0

Status:

BATP = 1, BATR = 0, FMCV = 0, FEDV = X,

FHTF = 0, FLTF = 0, tOUT = 0

The chip enters the charge mode when the proper mode

command bits are set and the power shutdown command

bit is clear. If a fault condition does not exist then charging

can begin. Charging will continue until a new command

word is input to change the mode or a fault condition

occurs.

The charge current may be regulated by a programmable

111kHz PWM buck current regulator, or by using the PFET

to gate an external current regulator or current limited

transformer.

111kHz PWM Controller

The block diagram of the charging loop connected as a

PWM buck current regulator is shown in Figure 4. The

PWM may operate in either continuous or discontinuous

mode. The loop forces the average voltage across the

sense resistor to be equal to the voltage at the output of the

DAC, so that the charging current becomes VDAC/RSENSE.

With switch S2 on and the others off, amplifier A1 along

with C1, R1 and R2 are configured as an integrator with

16kHz bandwidth. The output of the integrator is the

average difference between the voltage across the sense

resistor and the DAC output voltage.

The rising edge of the oscillator waveform triggers the one

shot which sets the flip-flop output high. This turns on the

external PFET P1 by pulling its gate low via the FET driver.

With P1 on, the current through the inductor L1 starts to

(MCV), minimum cell voltage exceeded (EDV), high tem-

perature limit exceeded (HTF), low temperature limit ex-

ceeded (LTF) and time limit exceeded (tOUT). When a fault

condition occurs, the discharge and charge loops are

disabled or prevented from turning on and the fail-safe bit

(FS) is set. The chip is reset by shifting in a new command

word with the fail-safe clear FSCLR bit set. The 8-bit status

word contains the state of each fault condition.

Power Shutdown Mode

Command: MOD1 = X, MOD0 = X, PS = 1

Status:

BATP = X, BATR = X, FMCV = X, FEDV = X,

FHTF = X, FLTF = X, tOUT = X

In the power shutdown mode, the analog section is turned

off and the supply current drops to 30

µA. The voltage

regulator, which provides power to the internal analog

circuitry and external bias networks, is shut down. The

voltage divider across the battery is disconnected and the

only circuit left on is the voltage regulator for the serial

interface logic.

Idle Mode

Command: MOD1 = 0, MOD0 = 0, PS = 0

Status:

BATP = X, BATR = X, FMCV = X, FEDV = X,

FHTF = X, FLTF = X, tOUT = X

The chip enters the idle mode when the proper mode

command bits are set and the power shutdown command

bit is cleared. During the idle mode, the chip is fully

powered, but the discharge, charge and gas gauge circuits

are off. The chip may be placed in the idle mode momen-

tarily while charging the battery, allowing an ADC mea-

surement to be made without any switching noise from the

PWM current source affecting the accuracy of the reading.

The mode command bits are picked off as they appear at

DIN, so that while the rest of the command word is being

shifted in, the charging loop has time to settle before an

ADC measurement is made.

Discharge Mode

Command: MOD1 = 0, MOD0 = 1, PS = 0

Status:

BATP = 1, BATR = 0, FMCV = X, FEDV = 0,

FHTF = 0, FLTF = 0, tOUT = 0

LTC1325CSW Datasheet(PDF) 13 Page - Linear Technology

LTC1325CSW Datasheet(HTML) 13 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL