6

LT1511

GND (Pins 1, 4, 5, 7, 16, 23, 24): Ground Pin.

SW (Pin 2): Switch Output. The Schottky catch diode must

be placed with very short lead length in close proximity to

SW pin and GND.

BOOST (Pin 3): This pin is used to bootstrap and drive the

switch power NPN transistor to a low on-voltage for low

55V.

UV (Pin 6): Undervoltage Lockout Input. The rising thresh-

old is at 6.7V with a hysteresis of 0.5V. Switching stops in

undervoltage lockout. When the supply (normally the wall

adapter output) to the chip is removed, the UV pin has to

be pulled down to below 0.7V (a 5k resistor from adapter

output to GND is required) otherwise the reverse battery

current drained by the chip will be approximately 200

µA

instead of 3

µA. Do not leave UV pin floating. If it is

undervoltage lockout will be effective.

OVP (Pin 8): This is the input to the amplifier VA with a

threshold of 2.465V. Typical input current is about 3nA out

of pin. For charging lithium-ion batteries, VA monitors the

battery voltage and reduces charging when battery voltage

reaches the preset value. If it is not used, the OVP pin

should be grounded.

CLP (Pin 9): This is the positive input to the supply current

limit amplifier CL1. The threshold is set at 100mV. When

used to limit supply current, a filter is needed to filter out

the 200kHz switching noise.

CLN (Pin 10): This is the negative input to the amplifier

CL1.

COMP1 (Pin 11): This is the compensation node for the

amplifier CL1. A 200pF capacitor is required from this pin

to GND if input current amplifier CL1 is used. At input

adapter current limit, this node rises to 1V. By forcing

COMP1 low with an external transistor, amplifier CL1 will

be defeated (no adapter current limit). COMP1 can source

200

µA.

SENSE (Pin 12): Current Amplifier CA1 Input. Sensing can

be at either terminal of the battery.

SPIN (Pin 13): This pin is for the internal amplifier CA1

Lithium Battery Charger (Figure 1).

BAT (Pin 14): Current Amplifier CA1 Input.

COMP2 (Pin 15): This is also a compensation node for the

amplifier CL1. It gets up to 2.8V at input adapter current

limit and/or at constant-voltage charging.

undervoltage lockout status. It stays low in undervoltage

state. With an external pull-up resistor , it goes high at valid

higher than 2V. Pull-up current should be kept under

100

µA.

the current mode PWM. Switching starts at 0.7V. Higher

operation. A capacitor of at least 0.33

µF to GND filters out

noise and controls the rate of soft-start. To shut down

switching, pull this pin low. Typical output current is 30

µA.

PROG (Pin 19): This pin is for programming the charging

current and for system loop compensation. During normal

GND the switching will stop. When a microprocessor

controlled DAC is used to program charging current, it

must be capable of sinking current at a compliance up to

2.465V.

good bypass, a low ESR capacitor of 20

µF or higher is

should be between 8V and 28V and at least 3V higher than

below SW by more than 0.7V with battery present. All three