Additional Application Circuits
5V
5V
R1
6.3K
R3
10K
V
OUT
Q1
Q2
Q3
Q2
FMMT2907ACT
FMMT2907ACT
FMMT2907ACT FMMT2907ACT
R2
1k
R1
24K
R4
10K
OVP OUT
TO V
FFB1
Q1
ENABLE 1
SIGNAL
FMMT2222ACT
TO COMP1
R2
5K
Q4
FMMT2222ACT
R3
1K
(R1 + R2)(0.65V)
R2
Figure 14: An external circuit can be built to provide an enable func-
tion for channel 1. The circuit shown above connects to the VFB1 and
COMP1 pins as indicated. If the ENABLE1 signal is left floating or is
pulled high, channel 1 is enabled. If the ENABLE1 pin is pulled
below 1V, Q1 will conduct, and mirror Q3 pulls VFFB1 up at the same
time as Q2 and Q4 pull COMP1 low. This will force GATE1 to go low
and turn off the switch FET. The circuit above will provide about
1mA of additional drive to the VFFB1 pin components. This additional
current must be sufficient to pull VFFB1 up to about 1V in order to
guarantee GATE1 is held low.
VOVP
=
Figure 12: Example external over voltage protection circuit. If VOUT
exceeds VOVP, OVP out goes high. Resistor values shown above pro-
vide a +10% tolerance for a 3.3V output.
5V
VOUT
PGOOD OUT
R1
18K
R3
10K
Q2
FMMT2222ACT
Q1
FMMT2222ACT
R2
5K
(R1 + R2)(0.65V)
VPGOOD
=
R2
Figure 13: Example external Power GOOD circuit. PGOOD(OUT) is low
until VOUT exceeds VPGOOD. VPGOOD is typically chosen to be 10%
below nominal VOUT. Resistor values above provide a -10% tolerance
on VOUT =3.3V.
15
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
