STSPIN840 datasheet(15/28 Pages) STMICROELECTRONICS

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DocID031835 Rev 1

15/28

STSPIN840

Detailed description

5.3

PWM current control

The device implements two independent PWM current controllers, one for each full bridge.

The bridge current is sensed through the SNS pins monitoring the voltage drop across an

external resistor connected between the source of the low side power MOSFET (SENSE

pins) and ground.

The voltage of the SNS pins (VSNSA and VSNSB) is compared to the respective reference

voltage pin (VREFA and VREFB).

When VSNSX > VREFX the current limiter is triggered, the OFF time counter is started and the

low sides of the full bridge are turned on (slow decay) until the end of count of the timer.

During current decays the inputs values are ignored until the system returns to ON condition

(decay time expired).

The reference voltage value, VREF, has to be selected according the load current target

value (peak value) and sense resistors value.

Equation 1

VREF = RSENSE ILOAD,peak

Table 8. ON and slow decay states

PHx(1)

1. When the device works in parallel mode the PHA and PWMA inputs drive both Full bridge A and B.

PWMx(1)

Slow decay

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

HSx1 = OFF

LSx1 = ON

HSx2 = ON

LSx2 = OFF

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

HSx1 = ON

LSx1 = OFF

HSx2 = OFF

LSx2 = ON

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

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