L9945 datasheet(21/151 Pages) STMICROELECTRONICS

21 / 151 page

Table 9. VPS supply block electrical characteristics

Symbol

Parameter

Test condition

Min.

Typ.

Max.

Unit

IVPS_OPM

IVPS operating mode current

VVPS_UV

VPS low battery detection threshold

3.5

3.8

tVPS_react

VPS Comparator output reaction time

100

700

tLBD_FIL

Filter time for VPS low battery detection

0.5

µs

5.2.3

VPS ADC

L9945 has an internal ADC monitoring VPS. Measure is obtained reading VPS_ADC[x] bit and applying the

following conversion law:

Eq. (2): Battery monitor conversion law

VPS=0.048×CODE

(2)

The table below reports the electrical characteristics of the VPS ADC.

Note:

Tj = Tj_op; all supplies are independent; 4.5 V < VDD5 < 5.5 V; 3.0 V < VIO < 5.5 V, unless otherwise noted.

Table 10. VPS ADC electrical characteristics

Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

ADC_res

Resolution

bit

fADC

Conversion rate

62.5

kHz

VPS_ADC_in

Input range VVPS

VPS_ACC

VVPS accuracy

3.5 V < VVPS < 12 V

-400

400

12 V < VVPS < 48 V

-3.3

3.3

5.2.4

Charge pump (VGBHI)

To effectively bias the high side drivers and fail safe switch, a charge pump is used to drive the gate voltage

above VPS. The charge pump switching frequency is nominally 200 KHz.

A built-in monitoring circuit checks if the charge pump output voltage is sufficient to control the high side valve

driver. In case of undervoltage (VGBHI < VCP_UV), the outputs are actively turned off and VCP_UV_LATCH is

set (readable via SPI, cleared on readout). The output of the undervoltage comparator can be monitored reading

VCP_UV_STATE via SPI.

At power ON, the charge pump is enabled when VDD5 is above VPOR and NRES is not asserted.

Refer to the AN: "Charge Pump Stress Estimation In Switching Applications" in order to understand how the

switching frequency of the outputs affects the charge pump behavior.

L9945

Supply concept

DS12275 - Rev 8

page 21/151

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