L9660 datasheet(19/49 Pages) STMICROELECTRONICS

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L9660

Functional description

3.2.3

Reference resistor

IREF pin shall be connected to VDD supply through a resistor, RIREF. When the L9660

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 L9660 goes in reset

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

conditions.

GND0-GND3

A loss of power-ground (GND0 – GND3) pin/s disables the respective low side driver/s on

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

Thus under the scenario where the low side is shorted to ground the L9660 is 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 is 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 and L9660 goes in reset condition. All outputs are

disabled and all internal register are reset to their default conditions.

3.2.5

VRESx capacitance

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

68nF is required close to the firing supply pins. Thus a minimum of 2 capacitors are required

with one placed close to the VRES0 and VRES1 pins and a second capacitor close to the

VRES2 and VRES3 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



VDD is used for all internal functions as well as short to battery/ground and high squib

resistance diagnostics.

3.2.7

Ground connections

GND pin (6) is not connected internally to other ground pins (AGND or power ground

GNDx). A ground plane is needed to directly connect the GND pin. This ground plane needs

to be isolated from the high current ground for the squib drivers to prevent voltage shifts.

AGND pin should be connected to ground plane too to minimize drop versus ground

reference of ADC that capture AOUT voltage.

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