LT1769IGN Linear Technology, LT1769IGN Datasheet - Page 8

• Manufacturer Part Number: LT1769IGN
• Description: IC CHARGER BATT CONST V/I 28SSOP
• Manufacturer: Linear Technology

Specifications of LT1769IGN

• Function: Charge Management
• Battery Type: Lead Acid, Li-Ion, NiCd, NiMH
• Voltage - Supply: 8 V ~ 25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP (0.150", 3.95mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LT1769
OPERATION
The LT1769 is a current mode PWM step-down (buck)
switcher. The battery DC charge current is programmed
by a resistor R
pin (see Block Diagram). Amplifier CA1 converts the
charge current through R
fed into the PROG pin. Amplifier CA2 compares the output
of CA1 with the programmed current and drives the PWM
control loop to force them to be equal. High DC accuracy
is achieved with averaging capacitor C
I
through R1 and generates a ramp signal that is fed to the
PWM control comparator C1 through buffer B1 and level
8
TEST CIRCUITS
PROG
has both AC and DC components. I
+
PROG
U
0.65V
(or a DAC output current) at the PROG
1k
0.047 F
S1
V
C
to a much lower current I
60k
–
+
LT1006
0.47 F
I
PROG
PROG
LT1769
CA2
. Note that
PROG
–
+
20k
R
PROG
PROG
V
10k
300
REF
1 F
PROG
goes
LT1769
Test Circuit 2
Test Circuit 1
+
1k
R
2.465V
PROG
PROG
VA
shift resistors R2 and R3, forming the current mode inner
loop. The BOOST pin drives the switch NPN Q
saturation and reduces power loss. For batteries like
lithium-ion that require both constant-current and con-
stant-voltage charging, the 0.5%, 2.465V reference and
the amplifier VA reduce the charge current when battery
voltage reaches the preset level. For NiMH and NiCd, VA
can be used for overvoltage protection. When the input
voltage is removed, the V
battery voltage, forcing the charger into a low battery drain
(3 A typical) sleep mode. To shut down the charger,
simply pull the V
+
–
–
+
LT1013
V
REF
10k
CA1
+
–
C
OVP
1769 TC02
pin low with a transistor.
BAT
SPIN
SENSE
CC
200
200
R
R
S3
S2
pin drops to 0.7V below the
R
100
S1
+
1769 TC01
V
BAT
SW
1769fa
into