LT1769 Linear Technology, LT1769 Datasheet - Page 6

• Manufacturer Part Number: LT1769
• Description: Constant-Current/ Constant-Voltage 2A Battery Charger with Input Current Limiting
• Manufacturer: Linear Technology

PIN
LT1769
GND (Pins 1 to 3, 7, 8, 14, 15, 22, 26 to 28): Ground Pins.
Must be connected to expanded PC lands for proper heat
sinking. See Applications Information section for details.
SW (Pin 4): Switch Output. The Schottky catch diode must
be placed with very short lead length in close proximity to
SW pin and GND.
BOOST (Pin 5): This pin is used to bootstrap and drive the
switch power NPN transistor to a low on-voltage for low
power dissipation. In Figure 1, V
switch is on. For lowest IC power dissipation, connect
boost diode D1 to a 3V to 6V at 30mA voltage source (see
Figure 10).
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 input supply (normally
the wall adapter output) to the IC is removed, the UV pin
must 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 IC will be approximately
200 A instead of 3 A. Do not leave the UV pin floating.
When connected to V
in 6.7V undervoltage lockout will be effective.
OVP (Pin 9): This is the input to amplifier VA with a
threshold of 2.465V. Typical bias current is about 3nA out
of this 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 10): This is the positive input to the input 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 11): This is the negative input to the input current
limit amplifier CL1.
COMP1 (Pin 12): This is the compensation node for the
input current limit amplifier CL1. 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 A. If this
function is not used, the resistor and capacitor on COMP1
pin, shown on the Figure 1 circuit, are not needed.
6
U
FUNCTIONS
U
U
IN
with no resistor divider, the built-
BOOST
= V
CC
+ V
BAT
when
SENSE (Pin 13): Current Amplifier CA1 Input. Sensing can
be at either terminal of the battery.
SPIN (Pin 16): This pin is for the current amplifier CA1
bias. It must be connected to R
Lithium Battery Charger (Figure 1).
BAT (Pin 17): Current Amplifier CA1 Input.
COMP2 (Pin 18): This is also a compensation node for
amplifier CL1. Voltage on this pin rises to 2.8V at input
adapter current limit and/or at constant-voltage charging.
UV
undervoltage lockout status. It stays low in undervoltage
state. With an external pull-up resistor, it goes high at valid
V
comes from CLN pin. UV
higher than 2V. Pull-up current should be kept under
100 A.
V
current mode PWM. Switching starts at 0.7V. In normal
operation, a higher V
current. A capacitor of at least 0.33 F to GND filters out
noise and controls the rate of soft start. To stop switching,
pull this pin low. Typical output current is 30 A.
PROG (Pin 21): This pin is for programming the charge
current and for system loop compensation. During normal
operation, V
GND switching will stop. When a microprocessor con-
trolled DAC is used to program charge current, it must be
capable of sinking current at a compliance up to 2.465V.
V
bypass, a low ESR capacitor of 15 F or higher is required,
with the lead length kept to a minimum. V
between 8V and 28V and at least 3V higher than V
Undervoltage lockout starts and switching stops when
V
parasitic diode from SW pin to V
below SW by more than 0.7V with battery present. All three
V
CC
C
CC1
CC
CC
OUT
(Pin 20): This is the inner loop control signal for the
. Note that the base drive of the open-collector NPN
goes below 7V typical. Note that there is an internal
pins should be shorted together close to the pins.
, V
(Pin 19): This is an open-collector output for
CC2
, V
PROG
CC3
(Pins 23 to 25): Input Supply. For good
stays close to 2.465V. If it is shorted to
C
OUT
corresponds to higher charge
stays low only when CLN is
CC
S1
pin. Do not force V
as shown in the 2A
CC
should be
BAT
CC
.