MC34167 ON Semiconductor, MC34167 Datasheet - Page 12

• Manufacturer Part Number: MC34167
• Description: (MC33167 / MC34167) Step-Up/Down/Inverting Switching Regulators
• Manufacturer: ON Semiconductor

Two potential problems arise when designing the standard voltage−inverting converter with the MC34167. First, the Switch Output emitter is
limited to −1.5 V with respect to the ground pin and second, the Error Amplifier’s noninverting input is internally committed to the reference and
is not pinned out. Both of these problems are resolved by connecting the IC ground pin to the converter’s negative output as shown in Figure 23.
This keeps the emitter of Q
drop across R
1
is equal to 5.05 V when the output is in regulation.
+
Figure 24. Voltage−Inverting Converter Printed Circuit Board and Component Layout
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. 5903B, or 5930B.
(Bottom View)
PWM
Line Regulation
Load Regulation
Output Ripple
Short Circuit Current
Efficiency
1
positive with respect to the ground pin and has the effect of reversing the Error Amplifier inputs. Note that the voltage
Oscillator
3.0″
3
Test
Thermal
Figure 23. Voltage−Inverting Converter
V
V
V
V
V
V
in
in
in
in
in
in
MC34167, MC33167
= 10 V to 24 V, I
= 12 V, I
= 12 V, I
= 12 V, R
= 12 V, I
= 24 V, I
http://onsemi.com
S
R
5
Q
Conditions
+
O
O
O
O
L
= 0.1 A to 1.7 A
= 1.7 A
= 1.7 A
= 1.7 A
= 0.1 W
12
ILIMIT
UVLO
Reference
0.47
C
O
F
= 1.7 A
EA
+
+
+
+
+
+
+
4.7 k
V in
+
R
F
Q
+
−
1
Î Î Î Î Î Î
Î Î Î Î Î Î
Î Î Î Î Î Î
Î Î Î Î Î Î
Î Î Î Î Î Î
Î Î Î Î Î Î
3.3 k
15 mV = ± 0.61%
4.0 mV = ± 0.020%
78 mV
5.7 A
79.5%
86.2%
4
2
1
R
2
+
12 V
V
in
Î Î Î
pp
Results
RF
330
−
C
2.4 k
190 mH
R
0.047
in
V O
C
1
L
1
(Top View)
1N5825
+
D
C F
1
+
4700
C
−12 V/1.7 A
O
+
V
O
+
+
+
+
+
+