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SIC402A

10 A microBUCK® SiC402A/B Integrated Buck Regulator with Programmable LDO

Vishay Semiconductors 

www.vishay.com

OPERATIONAL DESCRIPTION

Device Overview

The SiC402A/B is a step down synchronous DC/DC buck

converter with integrated power MOSFETs and a 200 mA

capable programmable LDO. The device is capable of

10 A operation at very high efficiency. A space saving

5 x 5 (mm) 32-pin package is used. The programmable

operating frequency of up to 1 MHz enables optimizing

the configuration for PCB area and efficiency.

The buck controller uses a pseudo-fixed frequency adaptive

on-time control. This control method allows fast transient

response which permits the use of smaller output

capacitors.

Input Voltage Requirements

The SiC402A/B requires two input supplies for normal

operation: VIN and VDD. VIN operates over a wide range from

3 V to 28 V. VDD requires a 3 V to 5.5 V supply input that can

be an external source or the internal LDO configured to

supply 3 V to 5.5 V from VIN.

Power Up Sequence

When the SiC402A/B uses an external power source at the

VDD pin, the switching regulator initiates the start up when

VIN, VDD and EN/PSV are above their respective thresholds.

When EN/PSV is at logic high, VDD needs to be applied after

VIN rises. It is also recommended to use a 10  resistor

between an external power source and the VDD pin. To start

up by using the EN/PSV pin when both VDD and VIN are

above their respective thresholds, apply EN/PSV to enable

the start-up process. For SiC402A/B in self-biased mode,

refer to the LDO section for a full description.

Shutdown

The SiC402A/B can be shut-down by pulling either VDD or

EN/PSV below its threshold. When using an external power

source, it is recommended that the VDD voltage ramps down

before the VIN voltage. When VDD is active and EN/PSV at

logic low, the output voltage discharges into the VOUT pin

through an internal FET.

Pseudo-Fixed Frequency Adaptive On-Time Control

The PWM control method used for the SiC402A/B is

pseudo-fixed frequency, adaptive on-time, as shown in

figure 23. The ripple voltage generated at the output

capacitor ESR is used as a PWM ramp signal. This ripple is

used to trigger the on-time of the controller.

SiC402A, SiC402BCD

Vishay Siliconix

VIN

Q1

Q2

tON

VLX

CIN

VLX

L

VFB

ESR

FB threshold

VOUT

FB

+

COUT

Fig. 23 - PWM Control Method, VOUT Ripple



The adaptive on-time is determined by an internal one-shot

timer. When the one-shot is triggered by the output ripple,

the device sends a single on-time pulse to the highside

MOSFET. The pulse period is determined by VOUT and VIN;

the period is proportional to output voltage and inversely

proportional to input voltage. With this adaptive on-time

arrangement, the device automatically anticipates the

on-time needed to regulate VOUT for the present VIN

condition and at the selected frequency.

The advantages of adaptive on-time control are:

• Predictable operating frequency compared to other

variable frequency methods.

• Reduced component count by eliminating the error

amplifier and compensation components.

• Reduced component count by removing the need to

sense and control inductor current.

• Fast transient response - the response time is controlled

by a fast comparator instead of a typically slow error

amplifier.

• Reduced output capacitance due to fast transient

response.

One-Shot Timer and Operating Frequency

The one-shot timer operates as shown in figure 24. The FB

comparator output goes high when VFB is less than the

internal 600 mV reference. This feeds into the gate drive and

turns on the high-side MOSFET, and also starts the

one-shot timer. The one-shot timer uses an internal

comparator and a capacitor. One comparator input is

connected to VOUT, the other input is connected to the

capacitor. When the on-time begins, the internal capacitor

charges from zero volts through a current which is

proportional to VIN. When the capacitor voltage reaches

VOUT, the on-time is completed and the high-side MOSFET

turns off.

S14-2048-Rev. C, 13-Oct-14

10

Document Number: 63729

For technical questions, contact: powerictechsupport@vishay.com

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

ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000

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