SMB117 datasheet(18/32 Pages) SUMMIT

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SMB113A/B/SMB117/A

Preliminary Information

Summit Microelectronics, Inc

2111 2.4 6/24/2008

APPLICATIONS INFORMATION

High Voltage Operation:

While the SMB113A has a max input voltage of 6.0V

the controller can operate to0 much higher voltages by

using the circuit depicted below. By inserting a

capacitor, C1, in series with the HSDRV gate signal

the HSDRV pin is isolated from the 12V supply, and

the AC coupling capacitor acts as a level translator

transferring the 0-5V signal from the HSDRV pin to a

12V to 7V (12V-5V = 7V) signal at the gate of the

PFET. When the gate stops switching the capacitor

becomes an open circuit and the gate will be pulled

high by R1 turning off the output. The schottky diode

and the pull-up resistor are used for DC restoration

and as a pull-up respectively.

Since the converter runs directly from the input supply

(12V in this instance) the efficiency is consistent with

that of a synchronous converter. Typical efficiency

curves are shown below.

LSDRV

HSDRV

AC Coupling capacitor

All power comes directly from 12V supply

DC Restoration

C45

22uF

C51

0.1uF

Schottky

C28

22uF

C33

0.1uF

3.3uH

Q2(P)

Q1(N)

FDC6420C

Vout

+12V

time

12V

Figure 7 – High-voltage operation

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