AN2833 datasheet(19/32 Pages) STMICROELECTRONICS

Part #	AN2833

Description	Dual step-down controller with auxiliary voltages for industrial system power

PDF	32 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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19 / 32 page

AN2833

Test setup and performance summary

19/32

11.2

Power-up

As shown in Figure 8 power-up starts when the input voltage is applied and the voltage on

the SHDN pin is above the SHDN on threshold (1.5 V). First LDO5 goes up with a masking

time of about 4 ms. If the LDO5 output is above the UVLO threshold at this time, the device

enters standby mode and the adjustable internal linear regulator LDO is turned on.

Figure 8.

REF, LDO5 and LDO power-up

11.3

Soft-start and shutdown waveforms

Figure 9, 10, 11 and 12 show respectively the soft-start and shutdown waveforms.

The PM681A has an independent internal digital soft-start for each switching section.

During the soft-start phase the internal current limit increases from 25% to 100% with steps

of 25% to avoid that the inductor current rises abruptly.

AM01443v1

AN2833 Datasheet(PDF) 19 Page - STMicroelectronics