AN3392 datasheet(16/57 Pages) STMICROELECTRONICS

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SPV1020 functions

AN3392

16/57

Doc ID 018749 Rev 1

6.3

Burst mode

This mode guarantees a correct startup for the SPV1020, avoiding voltage oscillations. After

the input voltage is applied, the converter begins operation when the input voltage exceeds

6.5 V (ULVO_H).

Burst mode contains four internal states, which guarantee to gradually activate phase “1”

and sequentially the four phases. Figure 13 shows the FSM of burst mode (the grey circles

are the burst mode states).

Each phase is driven with a set of 10 “pulses”. Each pulse can be “ON”, driving the phase

with a signal at a minimum PWM duty cycle of 5%, or “OFF”, with the driving signal

completely low.

When activated, a phase is driven with 1 pulse “ON” and 9 pulses “OFF”. The number of

“ON” pulses can be increased up to 10 (in this case, another phase is activated), or

decreased down to 0 (the phase is always OFF).

An increase or decrease of “ON” pulses depends on the status of the ULVO signal that

checks if the input voltage is greater than the minimum threshold or not.

Figure 13.

Burst mode FSM

When all four phases are active, the system enters normal (or MPPT) mode.

6.4

Normal/MPPT mode

This mode guarantees the maximum power extraction from a photovoltaic input supply by

executing an MPPT algorithm.

The MPPT algorithm generates a voltage reference (Vref) for a PWM generator. The

resulting waveform, with a duty cycle (DC) proportional to Vref, drives the eight internal

switching elements.

Only Phase “1” is active

•n pulses @DC=5%

• (10-n) pulses @DC=0%

[UVLO is ON]

OFF State

[UVLO is OFF]

[UVLO is ON]

[Check UVLO]

[n = 1]

If UVLO is ON [n = n+1]

else [n = n -1]

[UVLO is OFF]

[n is 1]

[UVLO is ON]

& [n is 10]

Phases 1 & 3 active

@DC=5%

Phases 1, 3 & 2 active

@DC=5%

Phases 1, 3, 2 & 4 active

@DC=5%

Normal

Mode

[UVLO is OFF]

[UVLO is ON]

[UVLO is OFF]

[UVLO is ON]

[UVLO is OFF]

AM02600v1

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