LP28400ACQVF datasheet(8/10 Pages) POWER

8 / 10 page

LP28400A – 02

Sep.-2016

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Page 8 of 10

Preliminary Datasheet

LP28400A

Battery Temperature Detection

The LP28400A continuously monitors temperature

by measuring the voltage between the THM and

GND pins. A negative or a positive temperature

coefficient thermistor (NTC, PTC) and an external

voltage divider typically develop this voltage. The

LP28400A compares this voltage against its internal

VTHM-L and VTHM-H thresholds to determine if

charging is allowed. The temperature sensing circuit

is immune to any fluctuation in VVL, since both the

external voltage divider and the internal thresholds

(VTHM-L)and VTHM-H) are referenced to VVL.

The resistor values of R1 and R2 are calculated by

the following equations:

For NTC Thermistors

For PTC Thermistors

K1(VTHM-L)=28% , K2(VTHM-H)=74%.

Where R(TC) is the cold temperature resistance and

R(TH) is the hot temperature resistance of thermistor,

as specified by the thermistor manufacturer. R1 or

R2 can be omitted if only one temperature (hot or

cold) setting is required. Applying a voltage between

the VTHM-L and VTHM-H thresholds to pin THM

disables the temperature-sensing feature.

Charge state indication

As showed below, the LED STAT respond to this five

STATES.

STATE

STAT Pin

LED STAT

Without Battery

Flicker

Charging

Low

Light On

Charge complete

High

Light Off

Vreg < Vreg(th)

Low

Light On

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