MC34166, MC33166
http://onsemi.com
10
4
2
1
5
3
+
C
F
R
F
R
1
1.5 k
C
O
1000
V
O
28 V/0.6 A
R
2
EA
Reference
Thermal
Oscillator
S
R
Q
PWM
UVLO
ILIMIT
V
in
12 V
C
in
330
+
6.8 k
4.7 k0.47
Q
1
D
1
1N5822
+
*Gate resistor R
G
, zener diode D
3
, and diode D
4
are required only when V
in
is greater than 20 V.
L
190 mH
*R
G
620
D
3
1N967A
D
2
1N5822
Q
2
MTP3055EL
D
4
1N4148
+
+
Test Conditions Results
Line Regulation V
in
= 8.0 V to 24 V, I
O
= 0.6 A 23 mV = ± 0.41%
Load Regulation V
in
= 12 V, I
O
= 0.1 A to 0.6 A 3.0 mV = ± 0.005%
Output Ripple V
in
= 12 V, I
O
= 0.6 A 100 mV
pp
Short Circuit Current
V
in
= 12 V, R
L
= 0.1 W
4.0 A
Efficiency V
in
= 12 V, I
O
= 0.6 A 82.8%
L = Coilcraft M1496−A or General Magnetics Technology GMT−0223, 42 turns of #16 AWG
on Magnetics Inc. 58350−A2 core.
Heatsink = AAVID Engineering Inc. MC34166: 5903B, or 5930B MTP3055EL: 5925B
Figure 21 shows that the MC34166 can be configured as a step−up/down converter with the addition of an external power MOSFET. Energy
is stored in the inductor during the on−time of transistors Q
1
and Q
2
. During the off−time, the energy is transferred, with respect to ground, to
the output filter capacitor and load. This circuit configuration has two significant advantages over the basic step−up converter circuit. The first
advantage is that output short−circuit protection is provided by the MC34166, since Q
1
is directly in series with V
in
and the load. Second, the
output voltage can be programmed to be less than V
in
. Notice that during the off−time, the inductor forward biases diodes D
1
and D
2
, transferring
its energy with respect to ground rather than with respect to V
in
. When operating with V
in
greater than 20 V, a gate protection network is required
for the MOSFET. The network consists of components R
G
, D
3
, and D
4
.
Figure 21. Step−Up/Down Converter
(Top View)
(Bottom View)
3.45″
″
1.9
Figure 22. Step−Up/Down Converter Printed Circuit Board and Component Layout
MC34166 STEP−UP/DOWN
V
in
V
O
C
O
C
in
L
C
F
RF
R2
R1
D1
+−
+−
+
+
D3
D2
R
G
Q2
