LTC1980
6
1980f
UU
U
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
pin and CA
OUT
(Pin 22) and another from PROGT to
ground. A capacitor between the PROGT pin and V
C
(Pin
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.
An external resistor divider from V
REG
to REGFB to ground
programs the output voltage. The virtual reference voltage
(V
REF
) on this pin is 1.225V. A series RC from the REGFB
pin to V
C
(Pin 4) provides pole-zero compensation for the
regulator outer loop.
V
C
(Pin 4): Control Signal of the Inner Loop of the Current
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
approximately 1V. Duty factor increases as V
C
increases.
This part includes slope compensation, so there is some
variation in V
C
for minimum and maximum duty factor as
V
REG
or V
BAT
is varied.
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-
tor. This pin is pulled up to V
REG
(shutting off the pass
transistor) if MODE (Pin 16) is grounded or if undervoltage
occurs.
V
REG
(Pin 7): Connection Point to the DC/DC Converter
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
Logic 1 = V
BIAS2
(Pin 19), Logic 0 = GND
RGTDR (Pin 11): DC/DC Converter (Regulator) Side Gate
Drive Pin. This pin provides gate drive to the external
MOSFET (REG-FET) that connects to V
REG
via the trans-
former.
PGND (Pin 12): Power Ground. Refer to the Applications
Information section for proper use of ground and power
ground connections.
V
BIAS1
(Pin 13): Internally Generated Power Bus. Bypass
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
MOSFET (BAT-FET) that connects to V
BAT
via the trans-
former.
