UM1556 datasheet(25/87 Pages) STMICROELECTRONICS

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UM1556

Analogue current sense

Doc ID 023520 Rev 2

25/87

encloses the geometric ratio, the current sense amplifier offset and various process

parameter spreads.

Care must be taken in order to ensure the ISENSE is proportional to IOUT. Indeed, the

maximum drop across the RSENSE is internally limited to approx. 7.5 V as specified in the

datasheet by the parameter VSENSE “maximum analog sense output voltage” (5 V minimum

@ 8 V <Vcc <16 V; -40°C < Tj <150 °C)

Example 1: VND5025AK with RSENSE selected to have VSENSE =1.5 V @ IOUT = 3 A

Considering (for sake of simplicity) K2 @ 3 A = 2790 (typical value) → ISENSE =1 mA→

RSENSE =1.5 k

Assuming a typical VSENSE saturation of 7.5 V → maximum ISENSE = 5 mA to maintain

linearity

→ maximum IOUT =14 A.

In other words, with the selected RSENSE any load current greater than 14 A produces

the same VSENSE (see Figure 26).

Figure 26.

VSENSE vs IOUT

On the other hand, care must be taken to prevent the P channel MOSFET M1 from

saturation, causing the ISENSE to again be disproportional with IOUT. This normally happens

when the maximum current that M1 is able to supply is reached (11 mA typ.)

This value is consistent with the current sense operating range and current limitation value.

Example 2: VND5025AK with RSENSE selected in order to have VSENSE =1.5 V @ IOUT

=10 A

Considering (for sake of simplicity) K3 @ 10 A = 2760 (typical value)

→ ISENSE =

3.6 mA

→ RSENSE = 414 Ω

Assuming K to remain approx. 2760 for IOUT > 10 A, the maximum load current which

can be detected is:

Main

sense

∝

UM1556 Datasheet(PDF) 25 Page - STMicroelectronics