A6986ITR datasheet(14/62 Pages) STMICROELECTRONICS

Part #	A6986ITR

Description	Automotive 38 V, 5 W synchronous iso-buck converter for isolated applications

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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Figure 9. Soft-start phase

The CSS value is chosen according to equation (1)

CSS = SSGAIN∙ISSCH∙TSS

VFB = 3∙4μA∙TSS

0.85V

(1)

where TSS is the soft-start time, ISS CH the charging current and VFB the reference of the error amplifier.

During normal operation a new soft-start cycle takes place in case of:

• Thermal shutdown event

• UVLO event

• The device is driven in INH mode

The soft-start capacitor is discharged with a 0.6 mA typ. current capability for 1 ms time max. For complete and

proper capacitor discharge in case of fault conditions, a maximum CSS = 67 nF value is suggested.

In case the soft-start should be externally driven by a voltage step (e.g. the signal from ignition switch in

automotive applications), the schematic in Figure 10 can be used.

The secondary output line regulation is defined, similarly to the primary side, as the variation of the secondary

output voltage due to the input voltage change at a specific current.

A6986I

Soft-start and inhibit

DS13481 - Rev 2

page 14/62

A6986ITR Datasheet(PDF) 14 Page - STMicroelectronics