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LTC4070

4070f

BLOCK DIAGRAM

4070 BD

3-STATE

DETECT

OSC

CLK

ADJ

1.5s

PULSED

DUTY CYCLE < 0.002%

30μs

NTCBIAS

NTC

RNOM

10k

–

REF

–

GND

DRV

HBO

LBO

VCC

ADC

NTHS0805N02N1002J

LTC4070

OPERATION

The LTC4070 provides a simple, reliable, and high perfor-

mance battery protection and charging solution by prevent-

ing the battery voltage from exceeding a programmed level.

Its shunt architecture requires just one resistor between

the input supply and the battery to handle a wide range

of battery applications. When the input supply is removed

and the battery voltage is below the high battery output

threshold, the LTC4070 consumes just 450nA from the

battery.

While the battery voltage is below the programmed float

voltage, the charge rate is determined by the input voltage,

the battery voltage, and the input resistor:

ICHG =

VIN − VBAT

()

RIN

As the battery voltage approaches the float voltage, the

LTC4070 shunts current away from the battery thereby

reducing the charge current. The LTC4070 can shunt up to

50mA with float voltage accuracy of ±1% over temperature.

The shunt current limits the maximum charge current, but

the 50mA internal capability can be increased by adding

an external P-channel MOSFET.

Adjustable Float Voltage, VFLOAT

A built-in 3-state decoder connected to the ADJ pin provides

three programmable float voltages: 4.0V, 4.1V, or 4.2V. The

float voltage is programmed to 4.0V when ADJ is tied to

GND, 4.1V when ADJ is floating, and 4.2V when ADJ is

tied to VCC. The state of the ADJ pin is sampled about

once every 1.5 seconds. When it is being sampled, the

LTC4070 applies a relatively low impedance voltage at the

ADJ pin. This technique prevents low level board leakage

from corrupting the programmed float voltage.

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