L9800 datasheet(28/55 Pages) STMICROELECTRONICS

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Power stages

The device is an 8-channel low-side relay switch. The power stages are made by N-channel Power MOSFET

transistors.

The source of the power transistors must be directly connected to the GND pin potential. An unwanted OV

detection may happen when a different voltage is applied.

7.1

Operating modes

The RDS(ON) (on-state resistance) depends on the TJ (junction temperature) and on the supply voltage.

7.1.1

Switching resistive loads

In the case of resistive loads switching, refer to the following switching times and slew rates.

Figure 20. Switching resistive load

VDS

tON

tOFF

% of

V /

tON

tOFF

tDELAY(ON)

tDELAY(OFF)

INn/

OUT.OUTn

70% ofVS

30% ofVS

10% ofVS

7.1.2

Inductive output clamp

The inductance still drives the current the voltage across the power switch increases until reaching VDS(CL) in

case of switching off inductive loads. The voltage clamping is necessary to prevent device destruction and

protects the device in all operative modes. The maximum allowed load inductance is limited by the max energy.

The clamping structure preserves the device in all the operating states: sleep, idle, active, and limp-home (see the

Figure 21).

Figure 21. Output clamp concept

DRAIN

SOURCE

Configurable channel

VDS(CL)

Control

Logic

L9800

Power stages

DS14041 - Rev 2

page 28/55

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