15105I データシートの表示（PDF） - Linear Technology

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15105I

Constant-Voltage/Constant-Current Battery Charger

Linear Technology 

LT1510/LT1510-5

TEST CIRCUITS

Test Circuit 2

LT1510

OVP

VA

IPROG

PROG

10k

VREF

10k

–

0.47µF RPROG

LT1013

+

+

2.465V

1510 TC02

U

OPERATIO

The LT1510 is a current mode PWM step-down (buck)

switcher. The battery DC charging current is programmed

by a resistor RPROG (or a DAC output current) at the PROG

pin (see Block Diagram). Amplifier CA1 converts the

charging current through RS1 to a much lower current

IPROG (500µA/A) fed into the PROG pin. Amplifier CA2

compares the output of CA1 with the programmed current

and drives the PWM loop to force them to be equal. High

DC accuracy is achieved with averaging capacitor CPROG.

Note that IPROG has both AC and DC components. IPROG

goes through R1 and generates a ramp signal that is fed to

the PWM control comparator C1 through buffer B1 and

level shift resistors R2 and R3, forming the current mode

inner loop. The Boost pin drives the switch NPN QSW into

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 charging current when battery

voltage reaches the preset level. For NiMH and NiCd, VA

can be used for overvoltage protection. When input volt-

age is not present, the charger goes into low current (3µA

typically) sleep mode as input drops down to 0.7V below

battery voltage. To shut down the charger, simply pull the

VC pin low with a transistor.

APPLICATIONS INFORMATION

Application Note 68, the LT1510 design manual, contains

more in depth appications examples.

Input and Output Capacitors

In the chargers in Figures 1 and 2 on the first page of this

data sheet, the input capacitor CIN is assumed to absorb all

input switching ripple current in the converter, so it must

have adequate ripple current rating. Worst-case RMS

ripple current will be equal to one half of output charging

current. Actual capacitance value is not critical. Solid

tantalum capacitors such as the AVX TPS and Sprague

593D series have high ripple current rating in a relatively

small surface mount package, but caution must be used

when tantalum capacitors are used for input bypass. High

input surge currents can be created when the adapter is

hot-plugged to the charger and solid tantalum capacitors

have a known failure mechanism when subjected to very

high turn-on surge currents. Highest possible voltage

rating on the capacitor will minimize problems. Consult with

the manufacturer before use. Alternatives include new high

8

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