SMB113A/B/SMB117/A
Preliminary Information
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.
12V
All power comes directly from 12V supply
5V
7V
time
time
Q2(P)
HSDRV
C1
0.1uF
Schottky
+12V
Q6
AC Coupling capacitor
R1
1K
C28
L1
3.3uH
DC Restoration
C33
0.1uF
1
Vout
Q1(N)
22uF
NP
FDC6420C
C45
C51
LSDRV
22uF
0.1uF
Figure 7 – High-voltage operation
Summit Microelectronics, Inc
2111 2.4 6/24/2008
18
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
