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
power dissipation. In normal operation, V
BOOST
= V
CC
+
V
BAT
when switch is on. Maximum allowable V
BOOST
is
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 200µA
instead of 3µA. Do not leave UV pin floating. If it is
connected to V
IN
with no resistor divider, the built-in 6.7V
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
200µA.
PIN FUNCTIONS
UUU
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
bias. It has to be connected to R
S1
as shown in the 3A
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.
UV
OUT
(Pin 17): This is an open collector output for
undervoltage lockout status. It stays low in undervoltage
state. With an external pull-up resistor , it goes high at valid
V
CC
. Note that the base drive of the open collector NPN
comes from CLN pin. UV
OUT
stays low only when CLN is
higher than 2V. Pull-up current should be kept under
100µA.
V
C
(Pin 18): This is the control signal of the inner loop of
the current mode PWM. Switching starts at 0.7V. Higher
V
C
corresponds to higher charging current in normal
operation. A capacitor of at least 0.33µF to GND filters out
noise and controls the rate of soft-start. To shut down
switching, pull this pin low. Typical output current is 30µA.
PROG (Pin 19): This pin is for programming the charging
current and for system loop compensation. During normal
operation, V
PROG
stays close to 2.465V. If it is shorted to
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.
V
CC
(Pins 20, 21, 22): This is the supply of the chip. For
good bypass, a low ESR capacitor of 20µF or higher is
required, with the lead length kept to a minimum. V
CC
should be between 8V and 28V and at least 3V higher than
V
BAT
. Undervoltage lockout starts and switching stops
when V
CC
goes below 7V. Note that there is a parasitic
diode inside from SW pin to V
CC
pin. Do not force V
CC
below SW by more than 0.7V with battery present. All three
V
CC
pins should be shorted together close to the pins.
