LTC4124 datasheet(13/30 Pages) AD

13 / 30 page

LTC4124

Rev. A

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APPLICATIONS INFORMATION

The LTC4124 is designed to be a highly integrated com-

plete solution for a wireless single cell Li-Ion battery char-

ger. As such its application circuit is simple with a minimal

number of external components.

COMPONENT SELECTION

In the simplest application with a DC input voltage and no

wireless power input, a single cell Li-Ion battery charger

with the LTC4124 requires no external components at all

(Figure 6). Note that even though this simplest application

is a complete functional single cell Li-Ion battery charger,

it does not have the temperature qualified charging feature

nor does it have any visual charge status indicator.

In order to include the temperature qualified charging, a

negative temperature coefficient (NTC) thermistor needs

to be added. To add a visual charge status indicator, an

LED needs to be connected between the VCC pin and the

CHRG pin. Figure 7 shows these two components added

to the application circuit of Figure 6.

Figure 6.

LTC4124

4124 F06

VCC

VSEL2

LBSEL

NTC

DCIN

BAT

ACIN

CHRG

PRECHG VSEL1 GND ISEL1 ISEL2

Simplest 10mA Single Cell Li-Ion Charger

with LTC4124 with No Temperature Qualified

Charging and No Charge Status Indicator

Figure 7.

RNTCRX

100k

DRX

LTC4124

4124 F07

VCC

VSEL2

LBSEL

CHRG

DCIN

NTC

BAT

ACIN

PRECHG

VSEL1 GND ISEL1 ISEL2

Simple 10mA Single Cell Li-Ion Charger with DC Input

NTC Thermistor

To use the battery temperature qualified charging feature,

connect a 100kΩ NTC thermistor between the NTC pin

and GND. Thermistor manufacturer data sheets usually

include either a temperature lookup table or a formula

relating temperature to the resistance at that correspond-

ing temperature. Table 5 shows some thermistors that can

be used with the LTC4124.

Table 5. Recommended NTC Thermistors

Manufacturer

Part Number

Description

TDK

NTCG064EF104F

100kΩ, 1%, 0201

MURATA

NCP03WF104F

100kΩ, 1%, 0201

In the setup shown in Figure 7, the LTC4124 will pause

charging at higher temperatures when the resistance of

the NTC thermistor drops to 54kΩ. For the thermistors

listed in Table 5, this corresponds to approximately 43°C.

As temperature drops, the resistance of the NTC thermis-

tor rises. The LTC4124 will also pause charging when the

value of the NTC thermistor increases to 300kΩ. For the

thermistors listed in Table 5, this corresponds to approxi-

mately 3°C. For the same thermistors in Table 5, the hot

and cold comparators each have approximately 5°C of

hysteresis to prevent oscillation about the trip point.

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