UM1556 datasheet(29/87 Pages) STMICROELECTRONICS

29 / 87 page

UM1556

Analogue current sense

Doc ID 023520 Rev 2

29/87

2.7

Diagnostics with different load configurations

2.7.1

Diagnostics with paralleled loads

A HSD with current sensing allows the detection of individual bulb failures when in a parallel

arrangement. However, if we consider the bulb wattage spread, the HSD K-factor tolerance,

variations of bulb currents vs. VBAT and ADC resolution, it is clear that accurate failure

determination can be difficult in some cases. For example, if there is a largeand small bulb

on the output, the detection limit for the lowest power bulb is lost in the tolerances.

In order to achieve better current sense accuracy, one or both of the strategies listed below

can be adopted:

Current sense calibration (K-factor measurement) of each HSD

VBAT measurement →bulb current compensation by appropriate software

2.7.2

Diagnostics with different load options

In some cases, the requirement profile asks for alternative loads to be driven with one and

the same High Side Driver. These load alternatives may be a bulb lamp alternating with an

LED (-cluster). In this case the driver:

●

must handle the high inrush current of the bulb load

●

must provide sufficiently low power dissipation during continuous operation

●

must not indicate an open load in case an LED (-cluster) is applied instead of a bulb.

M0-5 drivers today offer an open load threshold (in case of drivers with digital status output)

that is usually low enough to prevent an open load detection in case an LED is connected.

If an analog current sense device is used, different sense resistors have to be used in order

to have the current sense band in the appropriate range matching the different load

currents.

An example of a current sense resistor switching circuit can be seen in the Figure 29. The

measured scale can be extended by RSENSE1, switched in parallel to RSENSE2 by MOSFET

Q1.

Table 6.

Paralleling bulbs – overview

5+5W

OK without calibration

7+7W

21+21W

27+27W

21+5W

Calibration and VBAT monitoring recommended

27+7W

21+21+5W

Calibration and VBAT monitoring necessary

27+27+7W

UM1556 Datasheet(PDF) 29 Page - STMicroelectronics

UM1556 Datasheet(HTML) 29 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

Datasheet Download

Link URL