L9945TR datasheet(25/144 Pages) STMICROELECTRONICS

25 / 144 page

Figure 12. Output pre-driver control

IPU

IPD

IPU

IPD

VGBHI

NFET ou

Ratings: CM = 50 V for 12 V systems, 100 V for 24 V and 48 V systems.

tput control

NONx = 0

SPI_ON_OUTxx = 1

NONx = 1

SPI_ON_OUTxx = 0

To load

battery

To load

ground

To load

VPS

RPU

NONx = 1

SPI_ON_OUTxx = 0

NONx = 0

SPI_ON_OUTxx = 1

PFET output control

GADG2702171056PS

The pull up/pull down currents can be programmed via SPI through the GCC_config_xx bit, as shown in the table

below:

Table 14. Selection of gate charge/discharge currents

GCC_config_xx

IPU / IPD [mA]

Limited by external resistor (RG)

Internally clamped to ICh0Gx/IDCh0Gx

In case GCC_config_xx is programmed "0b00", an external resistor RG is required for protecting the transistor

gate against excessive current: the resistor must be mounted in series on the IPU / IPD path, as shown in

Figure 12. However, to prevent charge pump stress, the device internally limits the maximum charge/discharge

current to ICh0Gx/IDCh0Gx (refer to Table 15).

External measures have to be taken to keep the external MOS reliably OFF in case of output three-state. For

external NMOS a gate pull down resistor RPD is needed and for external PMOS a gate pull up resistor RPU is

necessary (refer to Figure 12).

In order to improve EMI behavior, an external Miller capacitor CM can be mounted between transistor gate and

drain. Value of this capacitor depends on:

•

The switching frequency required by the application;

•

The programmed charge/discharge current.

The AN "How To Improve EMI Behavior In Switching Applications" provides a guideline for CM selection. It also

helps choosing the right value for IPU/IPD in order to reduce EMI.

5.4.5

Internal and external clamping

The device guarantees a maximum gate to source voltage of 20 V by means of an internal clamping circuitry

which limits the overdrive. However, such a clamp is not intended as a protection against external spikes or

failures (STB/STG).

L9945

Functional description

DS12275 - Rev 10

page 25/144

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