STSPIN250 datasheet(15/26 Pages) STMICROELECTRONICS

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DocID029872 Rev 2

15/26

STSPIN250

Device description

6.3

PWM current control

The device implements a current controller.

The voltage on the sense pins (VSENSE) is compared to the reference voltage applied on the

REF pin (VREF).

When VSENSE > VREF, the current limiter is triggered, the OFF time counter is started, and

the decay sequence is performed.

The decay sequence starts turning on all the low sides of the full-bridge. After the

programmed OFF time the system returns to the ON state.

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

value (peak value) and sense resistors value.

Equation 1

VREF = RSNSx  ILOAD,peak

In choosing the sense resistors value, two main issues must be taken into account:



The sensing resistor dissipates energy and provides dangerous negative voltages on

the SENSE pins during the current recirculation. For this reason the resistance of this

component should be kept low (using multiple resistors in parallel will help obtaining

the required power rating with standard resistors).



The lower is the RSNSx value, the higher is the peak current error due to noise on the

VREF pin and to the input offset of the current sense comparator: too low values of

RSNSx must be avoided.

Table 9. ON and slow decay states

PWM

Decay

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

N.A.(1)

1. During decays the input values are ignored until the system returns to ON condition (decay time expired).

HSx1 = OFF

LSx1 = ON

HSx2 = ON

LSx2 = OFF

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

N.A.(1)

HSx1 = ON

LSx1 = OFF

HSx2 = OFF

LSx2 = ON

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

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