Datasheet LTC1980 (Analog Devices) - 6

LTC1980
U U U PI FU CTIO S PROG (Pin 1):
Charge Current Ratio Programming Pin.
VREG (Pin 7):
Connection Point to the DC/DC Converter Programs the full charge current when the charger is in the Side of the Combo Charger/Converter Circuit. constant current mode. A resistor placed between the
WA (Pin 8):
Wall Adapter Comparator Input. An external PROG pin and the PROGT pin (Pin 2) determines the resistor divider from the wall adapter output to WA to charge current. The PROG pin connects to an open drain ground sets the threshold which determines if charging MOSFET which turns on for full current and is off when can occur. If the wall adapter is below this threshold, the trickle charging. LTC1980 assumes the wall adapter is not present and the
PROGT (Pin 2):
Trickle Charge Programming Pin. Pro- charger shuts down. Wall adapter sense threshold is set grams the trickle charge current for a deeply discharged higher than the DC/DC converter output voltage to insure battery. Two resistors are used, one between the PROGT correct operation. pin and CAOUT (Pin 22) and another from PROGT to
BATT1 (Pin 9):
Logic Input Pin for Selecting ground. A capacitor between the PROGT pin and VC (Pin Preprogrammed Li-Ion Charge Voltage. See Truth Table 4) provides compensation for the constant current feed- logic settings. back loop.
BATT2 (Pin 10):
Logic Input Pin for Selecting
REGFB (Pin 3):
DC/DC Converter Feedback Pin. This pin is Preprogrammed Li-Ion Charge Voltage. The following used to program the DC/DC converter output voltage when combinations of BATT1 and BATT2 select the correct Li- the LTC1980 is in the DC/DC (regulator) converter mode. Ion charge voltage. See Truth Table. An external resistor divider from VREG to REGFB to ground programs the output voltage. The virtual reference voltage
BATT2 BATT1 FLOAT VOLTAGE
(VREF) on this pin is 1.225V. A series RC from the REGFB 0 0 4.1V pin to VC (Pin 4) provides pole-zero compensation for the 0 1 4.2V regulator outer loop. 1 0 8.2V
V
1 1 8.4V
C (Pin 4):
Control Signal of the Inner Loop of the Current Mode PWM. A common current mode loop is used by the Don’t Care Open Externally Set Via OVP battery charger and voltage regulator functions. Minimum Logic 1 = VBIAS2 (Pin 19), Logic 0 = GND duty factor (measured on BGTDR (Pin 14) in regulator
RGTDR (Pin 11):
DC/DC Converter (Regulator) Side Gate mode and RGTDR (Pin 11) in charger mode) occurs at Drive Pin. This pin provides gate drive to the external approximately 1V. Duty factor increases as VC increases. MOSFET (REG-FET) that connects to VREG via the trans- This part includes slope compensation, so there is some former. variation in VC for minimum and maximum duty factor as V
PGND (Pin 12):
Power Ground. Refer to the Applications REG or VBAT is varied. Information section for proper use of ground and power
LDOFB (Pin 5):
Low Dropout Regulator Feedback Pin. ground connections. This pin is used to program the low dropout linear regula- tor output voltage. An external resistor divider from the
VBIAS1 (Pin 13):
Internally Generated Power Bus. Bypass output of the LDO regulator (drain of the external MOSFET) this pin with a 1µF or larger ceramic capacitor (or other low to LDOFB to ground programs the output voltage. The ESR capacitor) to PGND (Pin 12). Do not connect any load virtual reference voltage on this pin is 1.225V. to this pin.
LDODRV (Pin 6):
Low Dropout Error Amplifier Output.
BGTDR (Pin 14):
DC/DC Converter (Battery) Side Gate This pin drives the gate of an external PMOS pass transis- Drive Pin. This pin provides gate drive to the external tor. This pin is pulled up to V MOSFET (BAT-FET) that connects to V REG (shutting off the pass BAT via the trans- transistor) if MODE (Pin 16) is grounded or if undervoltage former. occurs. 1980f 6