SPSA068 datasheet(21/49 Pages) STMICROELECTRONICS

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4.7

Spread spectrum

SPSA068 features a triangular-modulation spread spectrum for 2.4 MHz at the modulation frequency of

Fspread_mod_2.4, while for 400 kHz at Fspread_mod_400. The modulation frequency can be fixed or variable

according to the SPI configuration: BUCK_SS_MAIN_FIXED_FMODE and BUCK_SS_AUX_FIXED_FMODE. In

case of BUCK_SS_MAIN_FIXED_FMODE = ’0’, the Fspread_mod_2.4 is randomically changed in a range of

Fspread_mod_rand_2.4, while in case of BUCK_SS_AUX_FIXED_FMODE = ’0’ the Fspread_mod_400 is changed in a

range of Fspread_mod_rand_400, to avoid emissions in the audio band, and it is superposed to a higher frequency

modulation of lower amplitude to ensure effectiveness in the whole frequency spectrum. Both spread spectrum’s

can be independently disabled by SPI.

4.8

Undervoltage and overvoltage (power-good)

Output voltages are monitored: undervoltage and overvoltage information is provided through SPI.

One SPI bit allows to select between two threshold options for each regulator.

The power on timeout for every regulator is a signal that is set to ‘1’ if BUCK or VREF are not switched on

after 3 ms. If the timeout expires, the relative power on the timeout is set and the device moves to REC state.

4.9

Temperature control

The PMIC has a thermal sensor with ADC, positioned at the center of the chip to continuously monitor the

temperature of the die.

In case the temperature reaches the thermal shutdown threshold, the outputs are shut down and the device

moves in REC state.

A temperature warning is signaled by the FAULT pin, written in a register and read out by SPI.

Temperature information is updated every 500 μs and it is coded in the digital domain in unsigned 8 bit word

provided into a SPI register.

Temperature is calculated with the following formula:

Temperature C∘ =1.3706×CHIP_TEMP<15:8>−77.402

(1)

SPSA068

Functional description

DS14755 - Rev 1

page 21/49

SPSA068 Datasheet(PDF) 21 Page - STMicroelectronics