UM1556 datasheet(78/87 Pages) STMICROELECTRONICS

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Paralleling of HSDs

UM1556

78/87

Doc ID 023520 Rev 2

Figure 61.

Direct connection of CS pins (not recommended) – Hybrid HSD

Direct connection of CS pins is not safe in following cases:

●

Loss of Vbat1 or Vbat2

●

Loss of GND connection

Loss of either Vbat1 or Vbat2 leads to an incorrect current sense signal. If Vbat2 is lost, U2

logic part is supplied by U1 current sense signal through the internal Vcc-CS clamp

structure. Therefore the voltage on CS bus drops and we no longer have an accurate

VSENSE reading.

If the GND connection of one device is lost, positive as well as negative ISO pulses on the

associated supply line are no longer clamped (considering no other devices connected on

this supply line). If the transient voltage is high enough to activate involved clamp structures,

there may be an unlimited current flow between both supply lines through the CS pins. This

current can lead to malfunction or even failure of one or both of the HSDs.

In order to ensure a valid current sense signal and to protect devices in all previously

described cases, we can add a diode in series to each CS pin (as previously described in

the case of monolithic devices – see Section 6.2.1: Monolithic HSDs supplied from different

supply lines).

6.2.3

Mix of monolithic and hybrid HSDs supplied from different supply lines

Paralleling CS pins of monolithic and hybrid HSDs is possible, however some precautions in

schematics should be applied if the HSDs are supplied from different supply lines. Direct

connection of CS pins (as shown in Figure 62) is not safe.

Logic

OUT

CS_DIS

GND

Vcc

Reverse

Bat. Prot.

Pwr Clamp

Logic

OUT

CS_DIS

GND

Vcc

Reverse

Bat. Prot.

Pwr Clamp

GND

Vbat1

GND

100nF/50V

Vbat2

GND

100nF/50V

GND

Rsense

GND

ADC_IN

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