L9662 datasheet(27/80 Pages) STMICROELECTRONICS

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L9662

Functional description

3.2.3

Reference resistor

IREF pin shall be connected to VDD supply through a resistor, RIREF. When the device

detects the resistor on IREF pin is larger than RIREF_H or smaller than RIREF_L, it goes

into a reset condition. All outputs are disabled and all internal registers are reset to their

default conditions.

3.2.4

Loss of ground

GND

When the GND pin is disconnected from PC-board ground, the ASIC goes in reset

condition. All outputs are disabled and all internal registers are reset to their default

conditions.

GND0-GND7

A loss of power-ground (GND0 – GND7) pin/s disables the respective low side driver/s on

SQLx. However, the high side driver of the respective channel will still be able to be turned

on. Thus under the scenario where the low side is shorted to ground the device will be able

to provide the programmed firing current for the specified time.

An open GNDx connection on any channel has no affect on the other channels. An open

GNDx condition will be detected using the low side MOS diagnostics.

AGND

The AGND pin is a reference for AOUT pin. When AGND loses its connection, the voltage

on AOUT pin is pulled up to VDD voltage. The rest of functionality and parametric is not

affected by a loss of AGND condition.

3.2.5

VRESx capacitance

To ensure all diagnostics function properly a typical capacitor of equal to or greater than

68nF is required for every 4 VRESx pins and located close to the supply pins. Thus a

capacitor will be placed close to the VRES0, 1,2, and 3 pins and a second capacitor will be

close to the VRES4, 5,6, and 7 pins.

3.2.6

Supply voltages

The primary current sources for the different functions of the ASIC are as follows:



VRESx - Firing currents along with HSS and HS FET diagnostic currents



VSDIAG - Squib resistance and HSS diagnostics



VSATS - Voltage and current necessary for satellite operation excluding period during

sync pulse



VSYNC - Sync pulse voltage



VDD will be used for all internal functions as well as short to battery/ground and high

squib resistance diagnostics.

3.2.7

Ground connections

The GND pins (6, 38, and 45) are all common internal to the ASIC. A ground plane is

needed to directly connect the GND pins together so that low impedance is maintained

between the two pins. This ground plane needs to be isolated from the high current ground

for the squib drivers to prevent voltage shifts.

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