UM1556 datasheet(28/87 Pages) STMICROELECTRONICS

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Analogue current sense

UM1556

28/87

Doc ID 023520 Rev 2

2.6

Current sense resistor calculation

The analogue M0-5 HSDs integrate a current sense which under normal circumstances

provides a voltage across an external shunt resistor (RSENSE), which is proportional to the

load current with an N/n ratio (the so-called K factor):

This allows monitoring of the current which flows through the load and the detection of fault

conditions such as open load, overload and short-circuit to GND leading to a thermal

shutdown. In case of a thermal shutdown (M0-5, M0-5Enhanced) or a Power Limitation (M0-

5Enhanced), the CSENSE pin is switched to a voltage source VSENSEH (VSENSEH =9V typ,

ISENSEHmax = 8 mA) for as long as the device remains in the thermal shutdown (Power

Limitation) mode. The voltage from the current sense resistor is usually connected through a

10 k

Ω protection resistor to the ADC input of the µC. For the VSENSEH level, the voltage is

limited by the µC internal ESD protection (~5.6 V) and the ADC shows maximum value

(0xFF in case of 8 bit resolution). The capacitor CF is used to improve the accuracy of the

ADC. This capacitor plus a 10 k

Ω serial resistor function as a low pass filter (>10 kHz) for

potential HF noise on the CSENSE line (especially if there is a long wire route to the

microcontroller).

Figure 28.

Current sense resistor

The RSENSE value definition example:

Consider the VN5016AJ (16 m

Ω) with a nominal load current IN = 5 A@VSENSE = 2 V and

typ K = 5000 (datasheet):

SENSE

SENSE ISENSE

⋅

SEN SE

OUT

------------- V

[]

⋅

SENSE

OU T

-----------------------

⋅

5000

---

⋅

κΩ

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