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L9634

4

CIRCUIT DESCRIPTION

OSD is an integrated circuit to be used in air bag systems. Its main functions are deployment of the air

bag and diagnostics of the SDM (Sensing Deployment Module). The OSD supports 8 de-ployment loops.

The main features of OSD IC are:

21V max (current and time are internally limited while power supply is externally lim-ited).

to -1V.

ground difference.

4.1

Power On Reset

VDD loss of regulation detection is filtered for tPOR prior to issue an internal reset. This filter is intended

to provide protection from short transients on VDD input. When VDD input voltage decreases below VRST

for tPOR, OSD undergoes an internal reset. OSD keeps all current sinks and current sources, except the

IPD, inactive and all outputs are driven to an inactive state and remains inactive as VDD decays down to

0V. When VDD rises above VRST, the outputs and the internal current sinks and current sources are en-

abled. When OSD is in reset, none of the outputs are momentarily turned on.

4.2

Deployment Drivers

The on chip deployment drivers are sized to deliver IDEPLOY. Deployment current and period are pro-

grammable via SPI. The high side driver survives deployment condition 1 and 2 as defined here below.

SQLx is shorted to ground (-1V) in these two conditions.

Table 8. Deployment Survivability Conditions

No.

Drivers

Conditions

Voltage

Duration

1.

SQHx

1.47A

VRESx = 40V; SQLx = -1V

1.7

Ω

2.5mS

2.

2.14A

VRESx = 21V; SQLx = -1V

1.7

Ω

4.5mS

3.

SQLx

2.14A

SQHx = 18V

1.7

Ω

4.5mS

Obsolete

Product(s)

- Obsolete

Product(s)