NCP1729
www.onsemi.com
14
Capacitors = 3.3 mF
+
6
4
2
3
1
OSC
+
V
in
5
−V
out
+
R
1
R
2
10 k
Figure 32. Line and Load Regulated Negative Output Voltage
An adjustable shunt regulator can be used with the shutdown input to give excellent closed loop regulation performance. The
shunt regulator acts as a comparator with a precise input offset voltage which significantly reduces the converter’s output
resistance and dramatically enhances the line and load regulation. For closed loop operation, the desired regulated output
voltage must be lower in magnitude than −V
in
. The output will regulate at a level of −V
ref
(R
2
/R
1
+ 1). The adjustable shunt
regulator can be from either the TLV431 or TL431 families. The comparator offset or reference voltage is 1.25 V or 2.5 V
respectively. The performance characteristics for the converter are shown below. Note that the dashed curve sections represent
the converter’s open loop performance.
−2.0
−3.0
−1.0
−4.0
−5.0
I
out
, OUTPUT CURRENT (mA)
V
out
, OUTPUT VOLTAGE (V)
030 7010 20 40 50 60
Figure 33. Load Regulation, Output Voltage vs.
Output Current
A
B
T
A
= 25°C
A 3.0 5.0 k
B 5.0 24 k
Curve V
in
(V)
R
2
(W)
−1.8
−4.2
V
out
(V)
10 k
10 k
R
1
(W)
−2.5
−3.5
−4.5
V
in
, INPUT VOLTAGE (V)
V
out
, OUTPUT VOLTAGE (V)
1.0 3.02.0 4.0 5.0 6
Figure 34. Line Regulation, Output Voltage vs.
Input Current
−1.5
I
out
= 25 mA
R
1
= 10 k
R
2
= 24 k
T
A
= 25°C
