AN4539 datasheet(22/33 Pages) STMICROELECTRONICS

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Voltage mode buck converter with synchronous rectification and fault protection

AN4539

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DocID026506 Rev 1

Voltage mode buck converter with synchronous

rectification and fault protection

In this section we will discuss:

•

Deadtime;

•

Digital FAULT protection;

•

Burst mode controller.

This example presents a voltage mode buck converter where the freewheeling diode is

replaced by a MOSFET for synchronous rectification purpose. This allows to increase the

converter efficiency by reducing the losses when the inductance is demagnetized into the

output capacitor.

Figure 9 shows the power stage topology. It includes the output voltage reading and an

over-current protection using the FAULT input, to have the converter shut-down when the

current exceed a programmable threshold. For simplicity, the current sensor and the

conditioning circuitry are not discussed here; the expected FAULT feedback on FLT1 input is

a digital signal (on PA12 input).

Figure 9. Voltage mode buck with synchronous rectification

The HRTIM is operating in continuous mode, and the PWMs signals are defined as

following:

•

TA1: Set on TA Period, reset on TA CMP2

•

TA2: complementary of TA1 with deadtime generator (identical rising and falling edge

deadtimes)

The converter is over-current protected with the FLT1 digital input, low level sensitive. The

TA1 and TA2 output are forced to the low level in case of FLT1 event, by programming a

positive output polarity and an inactive fault state.

Figure 10 shows the buck control waveforms on TA1 and TA2 outputs and includes the case

where a fault occurs.

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