UM1557 datasheet(31/111 Pages) STMICROELECTRONICS

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UM1557

Analogue current sense

Doc ID 023521 Rev 2

31/111

Example for the chosen device:

Setting Iref1 = 2 A and Iref2 = 4 A according to Table 4 we get Vsense1 = 1.563 V and

Vsense2 = 3.115 V then

M=1.289 [S]

b= -0.014 [A]

Iout is then:

Iout = 1.289*Vsense - 0.014

(5)

After calibration, the current sense variation is still influenced by the device temperature.

Equation (5) is still affected by an error proportional to the sense current thermal drift.

This drift is reported in the datasheet as dK/K. The drift decreases when increasing the

output current.For example, in the VND5T035AK datasheet, the drift is +/-15 % at 2 A and it

decreases down to +/-5 % when the output current is 10 A.

3.5.4

Open load detection in off-state

●

Available if FR_Stby pin is set high

●

Indicated by VSENSEH on CS pin

●

External pull-up on the output needed

●

Possibility to distinguish between open load in off-state and short to VBAT using

switchable pull-up resistor.

Figure 24.

Analogue HSD–open load detection in off-state

Rgnd

4.7k

Dgnd

GND

56k

GND

Rsense

56k

GND

Vbat

GND

OUTPUT

GND

+5V

GND

Vdd

GND

out

ADC in

Microcontroller

100nF

1nF

100nF

10nF

22k

Vbat

Logic

OUT

FR_Stby

GND

Vcc

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