STPM066S datasheet(24/67 Pages) STMICROELECTRONICS

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VBATx can be read from 0 to 44 V:

Decimal=23.27×VBATxx=1,2 −1

(5)

VBATx=decimal+1

23.27

(6)

Example:

When the read out SPI register is 0x145, the decimal is 325 and VBAT1 = 14 V.

If the read out of SPI register is 0x28B, the decimal is 651 and VBAT1 = 28 V.

4.2.12

Maximum Duty Cycle and Refresh Mode for Buck

The high-side N-channel MOSFET is turned on at the beginning of each clock cycle and kept on until the inductor

current reaches its peak value as set by the regulation loop. Once the high side power is turned OFF, and after

a small delay (shoot-through delay), the lower N-channel MOSFET is turned on until the start of the next clock

cycle.

In dropout operation the high-side MOSFET can stay on 100%. To ensure the bootstrap capacitor is recharged,

the buck low-side power is forced off time (140ns) per 4 cycles. It is called “refresh mode”. This forced OFF time

limits the maximum duty cycle of the buck to:

Dmax=1−fsw⋅tOFF⋅0.25

(7)

The actual maximum duty cycle varies with the switching frequency.

Figure 13. Refresh mode in bucks

4 cycles

fSW_buck

PH_buck

tOFF_refresh

GADG0509181611PS

4.2.13

Frequency-Hopping Spread Spectrum

STPM066S features a pseudo-random spectrum for 2.4 MHz switching frequency, and a triangular spread

architecture for 400 kHz switching frequency. The frequency shifts only by one step at each cycle to avoid large

jumps in bucks and boost switching frequencies.

STPM066S

Voltage regulators and features description

DS12976 - Rev 2

page 24/67

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