Datasheet LT1511 (Analog Devices) - 8

LT1511
TEST CIRCUITS Test Circuit 1
SPIN LT1511 RS3 – SENSE 200Ω + VC R R S1 CA2 CA1 S2 10Ω + BAT 200Ω 1k 0.047 60k – µF + VBAT VREF PROG 1µF 300Ω RPROG + LT1006 1k 1511 • TC01 – + ≈ 0.65V 20k
Test Circuit 2
LT1511 OVP + VA – V PROG REF 10k IPROG 10k – LT1013 + + 0.47µF RPROG 2.465V 1511 • TC02
U OPERATION
The LT1511 is a current mode PWM step-down (buck) R2 and R3, forming the current mode inner loop. The switcher. The battery DC charging current is programmed Boost pin drives the switch NPN QSW into saturation and by a resistor RPROG (or a DAC output current) at the PROG reduces power loss. For batteries like lithium-ion that pin (see Block Diagram). Amplifier CA1 converts the require both constant-current and constant-voltage charg- charging current through RS1 to a much lower current ing, the 0.5%, 2.465V reference and the amplifier VA IPROG fed into the PROG pin. Amplifier CA2 compares the reduce the charging current when battery voltage reaches output of CA1 with the programmed current and drives the the preset level. For NiMH and NiCd, VA can be used for PWM loop to force them to be equal. High DC accuracy is overvoltage protection. When input voltage is not present, achieved with averaging capacitor CPROG. Note that IPROG the charger goes into low current (3µA typically) sleep has both AC and DC components. IPROG goes through R1 mode as input drops down to 0.7V below battery voltage. and generates a ramp signal that is fed to the PWM control To shut down the charger, simply pull the VC pin low with comparator C1 through buffer B1 and level shift resistors a transistor. 8