LTC1759 datasheet(8/28 Pages) LINER

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LTC1759

VC (Pin 27): This is the control signal of the inner loop of

the current mode PWM. Switching starts at 0.9V. Higher

VC corresponds to higher charging current in normal

operation. A capacitor of at least 0.33

µFtoAGNDfiltersout

noise and controls the rate of soft start.

PROG (Pin 28): This pin is for programming the charging

current and for system loop compensation. During normal

operation, the pin voltage is approximately 2.465V.

SENSE (Pin 29): Current Amplifier CA1 Input. Sensing

must be at the positive terminal of the battery.

SPIN (Pin 30): This pin is for the internal amplifier

CA1 bias. It must be connected to RSENSE as shown in

Figure 1.

BAT1 (Pin 31): Current Amplifier CA1 Input.

BOOSTC (Pin 33): This pin is used to bootstrap and supply

the current sense amplifier CA1 for very low dropout

conditions. VCC can be as low as only 0.4V above the

battery voltage. A diode and a capacitor are needed to get

the voltage from VBOOST. If low dropout is not needed and

VCC is always 3V or greater than VBAT, this pin can be left

floating or tied to VCC. Do not force this pin to a voltage

lower than VCC.

BGATE (Pin 35): Drives the gate of the bottom external

N-channel FET of the charger buck converter.

Monitor/Fault Diagnostic Pins

DCDIV (Pin 21): Supply Divider Input. This is a high

impedance comparator input with a 1V threshold (rising

edge) and hysteresis.

DCIN (Pin 22): Input connected to the DC input source to

monitor the DC input for power-fail condition.

BAT2 (Pin 23): Sensing Point for Voltage Control Loop.

Connect this to the positive terminal of the battery.

Internal Power Supply Pins

AGND (Pin 6): DC Accurate Ground for Analog Circuitry.

VDD (Pin 16): Low Voltage Power Supply Input. Bypass

this pin with 0.1

µF.

DGND (Pin 18): Ground for Digital Circuitry and DACs.

Should be connected to AGND at the negative terminal

of the charger output filter capacitor.

VCC (Pin 32): Power Input for Battery Charger Section.

Bypass this pin with 0.47

µF.

GBIAS (Pin 34): 8.6V Regulator Output for Bootstrapping

VBOOST and VBOOSTC. A bypass capacitor of at least 2µF is

needed. Switching will stop if VBOOST drops below 7.1V.

PGND (Pin 36): High Current Ground Return for Charger

Gate Drivers.

SBS Interface Pins

INTB (Interrupt Bar) (Pin 13): Active Low Interrupt Output

to Host. Signals host that there has been a change of status

in the charger registers and that the host should read the

LTC1759 status registers to determine if any action on its

part is required. This signal can be connected to the

optional SMBALERT# line of the SMBus. Open drain with

weak current source pull-up to VDD (with Schottky to allow

it to be pulled to 5V externally, see Figure 2).

SDA (Pin 14): SMBus Data Signal from Main (Host-

controlled) SMBus.

SCL (Pin 15): SMBus Clock Signal from Main (Host-

Controlled) SMBus. External pull-up resistor is required.

THERM (Pin 19): Thermistor Force/Sense Pin to Smart

Battery. See Electrical Characteristics table for more

detail. Maximum allowed combined capacitance on THERM

and RNR is 75pF.

RNR (Pin 20): Thermistor Force/Sense Pin to Smart

Battery. See Electrical Characteristics table for more

detail. Maximum allowed combined capacitance on THERM

and RNR is 75pF.

PIN FUNCTIONS

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