L6924UTR datasheet(25/37 Pages) STMICROELECTRONICS

25 / 37 page

L6924U

Application information: monitoring and protection

Doc ID 14716 Rev 2

25/37

charge the battery, only when the voltage at the TH pin goes under VMINTH_HYS = 780 mV

(typ).

For what concerns the high temperature limit, when the TH pin voltage falls under the

VMAXTH = 12.5 % of VREF (225 mV Typ.), the L6924U stops the charge until the TH pin

voltage reaches the VMAXTH_HYS = 248 mV (typ.).

When the battery is at the low temperature limit, the TH pin voltage is 900 mV. The correct

resistance ratio to set the low temperature limit at 0 °C can be found with the following

equation:

Equation 12

Where RUP is the pull-up resistor, VREF is equal to 1.8 V, and RNTC0°C is the value of the

NTC at 0 °C. Since at the low temperature limit VMINTH = 900 mV:

Equation 13

It follows that:

Equation 14

Similarly, when the battery is at the high temperature limit, the TH pin voltage is 225 mV. The

correct resistance ratio to set the high temperature limit at 50 °C can be found with the

following equation:

Equation 15

Where RNTC50°C is the value of the NTC at 50 °C. Considering VMAXTH = 225 mV it follows

that:

Equation 16

Consequently:

Equation 17

NTC

REF

MINTH

NTC

REF

MAXTH

NTC

225

NTC

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