L6474 datasheet(18/51 Pages) STMICROELECTRONICS

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Functional description

L6474

18/51

Doc ID 022529 Rev 2

Functional description

6.1

Device power-up

At power-up end, the device state is the following:

●

Registers are set to default

●

Internal logic is driven by internal oscillator and a 2 MHz clock is provided by the

OSCOUT pin

●

Bridges are disabled (High Z)

●

UVLO bit in STATUS register is forced low (fail condition)

●

FLAG output is forced low.

During power-up the device is under reset (all logic IO disabled and power bridges in high

impedance state) until the following conditions are satisfied:

●

VS is greater than VSthOn

●

VREG is greater than VREGth = 2.8 V typical

●

Internal oscillator is operative.

6.2

Logic I/O

Pins CS, CK, SDI, STCK, DIR and STBY\RST are TTL/CMOS 3.3 V-5 V compatible logic

inputs.

Pin SDO is a TTL/CMOS compatible logic output. VDD pin voltage sets the logic output pin

voltage range; when it is connected to VREG or 3.3 V external supply voltage, the output is

3.3 V compatible. When VDD is connected to a 5 V supply voltage, SDO is 5 V compatible.

VDD is not internally connected to VREG, an external connection is always needed.

A 10 µF capacitor should be connected to the VDD pin in order to obtain a proper operation.

Pins FLAG and SYNC are open drain outputs.

6.3

Charge pump

To ensure the correct driving of the high side integrated MOSFETs, a voltage higher than

the motor power supply voltage needs to be applied to the VBOOT pin. The high side gate

driver supply voltage VBOOT is obtained through an oscillator and a few external

components realizing a charge pump (see Figure 5).

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