STSPIN820 datasheet(16/29 Pages) STMICROELECTRONICS

16 / 29 page

Functional description

STSPIN820

16/29

DocID031065 Rev 2

5.3

PWM current control

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

The voltage of the sense pins (VSNSA and VSNSB) is compared to the respective internal

reference voltage based on the sequencer value (seeTable 8 and Table 9).

When VSNSX > VREFX the integrated comparator is triggered, the OFF time counter is

started and the decay sequence is performed.

The decay sequence starts turning on both the low sides of the full-bridge (slow decay),

after the behavior of the PWM current control depends on the DECAY input:



When the DECAY input is low (mixed decay): the system switches from slow decay

to quasi-synchronous fast decay (the sinking side of the bridge is put in high

impedance) when the counter reaches a fixed threshold corresponding to a 5/8th of the

total decay time (tOFF).

As soon as the counter reaches the end of the count it is reset and the bridges return in

the ON state.



When the DECAY input is high (slow decay only): the system stays in slow decay

until the counter reaches the end of the count, then it is reset and the bridges returns in

the ON state.

The description of the ON, slow decay and fast decay status are listed in Table 11.

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

value (peak value) and the sense resistors value.

Equation 1

VREF = RSNS · ILOAD,peak

Table 11. ON, slow decay and fast decay states

Current direction(1)

1. The current direction is set according to Table 8 or Table 9.

Slow decay

Fast decay

(quasi-synch.)

Zero

(power bridge

disabled)

HSX1 = OFF

LSX1 = OFF

HSX2 = OFF

LSX2 = OFF

HSX1 = OFF

LSX1 = OFF

HSX2 = OFF

LSX2 = OFF

HSX1 = OFF

LSX1 = OFF

HSX2 = OFF

LSX2 = OFF

X1 → X2

HSX1 = ON

LSX1 = OFF

HSX2 = OFF

LSX2 = ON

HSX1 = OFF

LSX1 = ON

HSX2 = OFF

LSX2 = ON

HSX1 = OFF

LSX1 = ON

HSX2 = OFF

LSX2 = OFF

X1 ← X2

HSX1 = OFF

LSX1 = ON

HSX2 = ON

LSX2 = OFF

HSX1 = OFF

LSX1 = ON

HSX2 = OFF

LSX2 = ON

HSX1 = OFF

LSX1 = OFF

HSX2 = OFF

LSX2 = ON

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