L9945 datasheet(24/144 Pages) STMICROELECTRONICS

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5.4

Output pre-drivers

This paragraph contains the available configurations for the output pre-drivers. Enable and control strategies are

explained. Output diagnostic is also explained, along with other useful application information.

5.4.1

Available configurations

There are eight pre-driver channels. Each channel can be independently configured in three different ways, via

SPI configuration commands:

•

Low-Side with NFET;

•

High-Side with NFET;

•

High-Side with PFET.

Channel side is programmed through LS_HS_config_xx bit, while FET type is selected through N_P_config_xx

bit. Refer to Section 2: Output configurations in order to understand how the external FET must be mounted with

respect to device pins. Complex configurations for H-Bridge and Peak & Hold are presented in their respective

section.

5.4.2

Default configuration and output enable

After reset channels are configured as Low-Side with NFET by default. Outputs are in three-state until they are

configured and enabled through the en_OUT_xx bit.

Channel 6 has an additional enable control via the EN6 input: EN6 is in logical AND with en_OUT_06 bit,

meaning that both signals have to be set high in order to enable the output driver. This feature makes it suitable

for safety relevant load control. EN6 status can be monitored reading EN6_STATE bit via SPI. If channel 6 has

been disabled setting EN6 low, the event is latched in EN6_LATCH, cleared on SPI readout.

5.4.3

Output control

The outputs can be controlled ON and OFF via SPI bit SPI_ON_OUTxx or input pins NONx. The selection of the

control signal is independent for each channel and is programmed via the SPI_input_sel_xx bit:

•

SPI_input_sel_xx = 0: control via NONx input

–

The NONx inputs are active low, meaning that the output is ON when the input is low and vice-versa

•

SPI_input_sel_xx = 1: control via SPI_ON_OUTxx bit

–

The SPI_ON_OUTxx bit are positive asserted, meaning that the output is ON when the input is high

and vice-versa

The table below summarizes output behavior depending on control strategy and control input.

Table 13. Output status depending on control strategy and control input

SPI_input_sel_xx

NONx

SPI_ON_OUTxx

External FET status

X(1)

OFF

1. All “X” = don't care.

5.4.4

Gate charge/discharge currents

During normal operation external FET is actively switched ON/OFF by means of a pull up/pull down current

source, as shown in Figure 12.

L9945

Functional description

DS12275 - Rev 10

page 24/144

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