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LT8490

8490f

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applicaTions inForMaTion

Figure 12. Battery Temperature Sensing Circuit

Figure 13. Stage 2 Voltage Limit vs Temperature

When Temperature Compensation Is Enabled

8490 F12

LT8490

GND

AVDD

TEMPSENSE

100nF

11.5k

CABLE

TO/FROM

CHARGER

10k NTC THERMISTOR

THERMALLY COUPLED

WITH BATTERY PACK

TO CHARGER OUTPUT

AT RSENSE2

When temperature compensated charging and Stage 3

are enabled, use:

CHARGECFG1% = 2.67 •

VS3

VS2

− 0.85

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟+0.55

⎡

⎣

⎢

⎤

⎦

⎥

• 100%

When temperature compensated charging is disabled and

Stage 3 is enabled, use:

CHARGECFG1% = 2.72− 2.67 •

VS3

VS2

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

⎡

⎣

⎢

⎤

⎦

⎥

• 100%

where VS3/VS2 should be between 0.86 to 0.99.

For example, to enable temperature compensated charg-

ing with VS3 set to 93% of VS2, choose a divider that puts

CHARGECFG1 at 76% of AVDD. For best accuracy use

resistors that have a 1% tolerance or better.

Temperature Measurement, Compensation and Fault

The LT8490 can measure the battery temperature using

an NTC (negative temperature coefficient) thermistor

thermally coupled to the battery pack. The temperature

monitoring function is enabled by connecting a 10kΩ,

ß = 3380 NTC thermistor from the TEMPSENSE pin to

ground and an 11.5kΩ (1% tolerance or better) resistor

from AVDD to TEMPSENSE (as shown in Figure 12). If

battery temperature monitoring is not required, then use a

10kΩ resistor in place of the thermistor. This will indicate

to the LT8490 that the battery is always at 25°C.

The LT8490 monitors the voltage on the TEMPSENSE pin

to determine the battery temperature and also to detect if

the thermistor is connected or not. A TEMPSENSE volt-

age greater than 96% of AVDD (typical) indicates that the

thermistorhasbeendisconnected.Threechargerfunctions

rely on the TEMPSENSE information.

1. INVALID BATTERY TEMPERATURE FAULT: A tempera-

turefaultoccurswhenthebatterytemperatureisoutside

ofthevalidrangeasconfiguredontheCHARGECFG2pin

(–20°C to 50°C or 0°C to 50°C). The temperature fault

condition remains until the temperature returns within

–15°Cto45°Cor5°Cto45°C(5°Cofhysteresis).During

a temperature fault, charging is halted and the STATUS

and FAULT pins follow the pattern described in Table 6.

If timer termination is enabled with the CHARGECFG2

pin, the timer count is paused during the temperature

fault and resumes when the fault state is exited.

2. BATTERY VOLTAGE TEMPERATURE COMPENSATION:

Some battery chemistries charge best when the voltage

limit is adjusted with battery temperature. Lead-acid

batteries, in particular, experience a significant change

in the ideal charging voltage as temperature changes. If

enabledwiththeCHARGECFG1pin,thebatterycharging

voltage and all related voltage thresholds are automati-

cally adjusted with battery temperature. As the voltage

on the TEMPSENSE pin changes, the PWM duty cycle

from the FBOW pin changes such that the voltage limits

of the LT8490 follow the curve shown in Figure 13.

BATTERY TEMPERATURE (°C)

–25

100

102

104

106

108

112

110

–5

–15

8490 F13

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