STSPIN240 datasheet(15/26 Pages) STMICROELECTRONICS

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DocID029313 Rev 3

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STSPIN240

Functional description

6.3

PWM current control

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

The voltage on the sense pins (VSENSEA and VSENSEB) is compared to the reference voltage

applied on the REF pin (VREF).

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

the decay sequence is performed.

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

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 resistor 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 to obtain 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

PHx

PWMx

Decay

HSx1 = OFF

LSx1 = ON

HSx2 = OFF

LSx2 = ON

N.A.(1)

1. During decays the inputs 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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