LTC1980

6

1980f

PI FU CTIO S

PROG (Pin 1): Charge Current Ratio Programming Pin.

Programs the full charge current when the charger is in the

constant current mode. A resistor placed between the

PROG pin and the PROGT pin (Pin 2) determines the

charge current. The PROG pin connects to an open drain

MOSFET which turns on for full current and is off when

trickle charging.

PROGT (Pin 2): Trickle Charge Programming Pin. Pro-

grams the trickle charge current for a deeply discharged

battery. Two resistors are used, one between the PROGT

4) provides compensation for the constant current feed-

back loop.

REGFB (Pin 3): DC/DC Converter Feedback Pin. This pin is

used to program the DC/DC converter output voltage when

the LTC1980 is in the DC/DC (regulator) converter mode.

programs the output voltage. The virtual reference voltage

regulator outer loop.

Mode PWM. A common current mode loop is used by the

battery charger and voltage regulator functions. Minimum

duty factor (measured on BGTDR (Pin 14) in regulator

mode and RGTDR (Pin 11) in charger mode) occurs at

This part includes slope compensation, so there is some

LDOFB (Pin 5): Low Dropout Regulator Feedback Pin.

This pin is used to program the low dropout linear regula-

tor output voltage. An external resistor divider from the

output of the LDO regulator (drain of the external MOSFET)

to LDOFB to ground programs the output voltage. The

virtual reference voltage on this pin is 1.225V.

LDODRV (Pin 6): Low Dropout Error Amplifier Output.

This pin drives the gate of an external PMOS pass transis-

transistor) if MODE (Pin 16) is grounded or if undervoltage

occurs.

Side of the Combo Charger/Converter Circuit.

WA (Pin 8): Wall Adapter Comparator Input. An external

resistor divider from the wall adapter output to WA to

ground sets the threshold which determines if charging

can occur. If the wall adapter is below this threshold, the

LTC1980 assumes the wall adapter is not present and the

charger shuts down. Wall adapter sense threshold is set

higher than the DC/DC converter output voltage to insure

correct operation.

BATT1 (Pin 9): Logic Input Pin for Selecting

Preprogrammed Li-Ion Charge Voltage. See Truth Table

logic settings.

BATT2 (Pin 10): Logic Input Pin for Selecting

Preprogrammed Li-Ion Charge Voltage. The following

combinations of BATT1 and BATT2 select the correct Li-

Ion charge voltage. See Truth Table.

BATT2

BATT1

FLOAT VOLTAGE

0

0

4.1V

0

1

4.2V

1

0

8.2V

1

1

8.4V

Don’t Care

Open

Externally Set Via OVP

RGTDR (Pin 11): DC/DC Converter (Regulator) Side Gate

Drive Pin. This pin provides gate drive to the external

former.

PGND (Pin 12): Power Ground. Refer to the Applications

Information section for proper use of ground and power

ground connections.

this pin with a 1µF or larger ceramic capacitor (or other low

ESR capacitor) to PGND (Pin 12). Do not connect any load

to this pin.

BGTDR (Pin 14): DC/DC Converter (Battery) Side Gate

Drive Pin. This pin provides gate drive to the external

former.