Datasheet LT1511 (Analog Devices) - 6

LT1511
U U U PIN FUNCTIONS GND (Pins 1, 4, 5, 7, 16, 23, 24):
Ground Pin.
SENSE (Pin 12):
Current Amplifier CA1 Input. Sensing can
SW (Pin 2):
Switch Output. The Schottky catch diode must be at either terminal of the battery. be placed with very short lead length in close proximity to
SPIN (Pin 13):
This pin is for the internal amplifier CA1 SW pin and GND. bias. It has to be connected to RS1 as shown in the 3A
BOOST (Pin 3):
This pin is used to bootstrap and drive the Lithium Battery Charger (Figure 1). switch power NPN transistor to a low on-voltage for low
BAT (Pin 14):
Current Amplifier CA1 Input. power dissipation. In normal operation, VBOOST = VCC +
COMP2 (Pin 15):
This is also a compensation node for the VBAT when switch is on. Maximum allowable VBOOST is amplifier CL1. It gets up to 2.8V at input adapter current 55V. limit and/or at constant-voltage charging.
UV (Pin 6):
Undervoltage Lockout Input. The rising thresh-
UV
old is at 6.7V with a hysteresis of 0.5V. Switching stops in
OUT (Pin 17):
This is an open collector output for undervoltage lockout status. It stays low in undervoltage undervoltage lockout. When the supply (normally the wall state. With an external pull-up resistor , it goes high at valid adapter output) to the chip is removed, the UV pin has to V be pulled down to below 0.7V (a 5k resistor from adapter CC. Note that the base drive of the open collector NPN comes from CLN pin. UV output to GND is required) otherwise the reverse battery OUT stays low only when CLN is higher than 2V. Pull-up current should be kept under current drained by the chip will be approximately 200µA 100µA. instead of 3µA. Do not leave UV pin floating. If it is connected to V
V
IN with no resistor divider, the built-in 6.7V
C (Pin 18):
This is the control signal of the inner loop of undervoltage lockout will be effective. the current mode PWM. Switching starts at 0.7V. Higher V
OVP (Pin 8):
This is the input to the amplifier VA with a C corresponds to higher charging current in normal operation. A capacitor of at least 0.33µF to GND filters out threshold of 2.465V. Typical input current is about 3nA out noise and controls the rate of soft-start. To shut down of pin. For charging lithium-ion batteries, VA monitors the switching, pull this pin low. Typical output current is 30µA. battery voltage and reduces charging when battery voltage reaches the preset value. If it is not used, the OVP pin
PROG (Pin 19):
This pin is for programming the charging should be grounded. current and for system loop compensation. During normal operation, V
CLP (Pin 9):
This is the positive input to the supply current PROG stays close to 2.465V. If it is shorted to GND the switching will stop. When a microprocessor limit amplifier CL1. The threshold is set at 100mV. When controlled DAC is used to program charging current, it used to limit supply current, a filter is needed to filter out must be capable of sinking current at a compliance up to the 200kHz switching noise. 2.465V.
CLN (Pin 10):
This is the negative input to the amplifier
V
CL1.
CC (Pins 20, 21, 22):
This is the supply of the chip. For good bypass, a low ESR capacitor of 20µF or higher is
COMP1 (Pin 11):
This is the compensation node for the required, with the lead length kept to a minimum. VCC amplifier CL1. A 200pF capacitor is required from this pin should be between 8V and 28V and at least 3V higher than to GND if input current amplifier CL1 is used. At input VBAT. Undervoltage lockout starts and switching stops adapter current limit, this node rises to 1V. By forcing when VCC goes below 7V. Note that there is a parasitic COMP1 low with an external transistor, amplifier CL1 will diode inside from SW pin to VCC pin. Do not force VCC be defeated (no adapter current limit). COMP1 can source below SW by more than 0.7V with battery present. All three 200µA. VCC pins should be shorted together close to the pins. 6