SiC437, SiC438

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Vishay Siliconix

S18-0030-Rev. B, 15-Jan-18

7

Document Number: 75921

THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT

For SiC43xA, the minimum switching frequency that the

regulator will drop to is 25 kHz as the part avoids switching

frequencies in the audible range to prevent audible noise. In

this version of the part, the light load mode, is called the

ultrasonic mode.



The SiC43x has a low pin count and minimum external

components. To offer the user maximum flexibility to choose

soft start times, current limit settings, switching frequencies

and to enable or disable the light load mode, just two MODE

pins are used and a particular resistor value connected to

modes.This is best explained by the below tables:

OUTPUT MONITORING AND PROTECTION FEATURES

Output Overcurrent Protection (OCP)

SiC43x has pulse-by-pulse overcurrent limit control. The

inductor valley current is monitored during LS FET turn-on

time, the valley current is compared with internal threshold

to determine the threshold for OCP. If monitored current

is higher than threshold, HS turn-on pulse is skipped and

LS FET is kept on until the valley current returns below

OCP limit.

In the severe over-current condition, pulse-by-pulse current

limit eventually triggers output undervoltage protection

(UVP) and the device will go into hiccup mode as described

in the next section.

Fig. 7 - Over-Current Protection Illustration

TABLE 1 - MODE 1 CONFIGURATION SETTINGS

OPERATION

CONNECTION

Skip

300

51

500

100

750

200

1000

500

Forced CCM

300

51

500

100

750

200

1000

500

TABLE 2 - MODE 2 CONFIGURATION SETTINGS

SOFT-START TIME

CONNECTION

4.5 ms

30

51

54

100

78

200

100 % (18 A on SiC437)

100 % (12 A on SiC438)

500

9 ms

30

51

54

100

78

200

100 % (18 A on SiC437)

100 % (12 A on SiC438)

500

I

load

OCP

threshold

I

inductor

GH