AND8031/D

http://onsemi.com

4

TL431

TLV431

NCP100

36

3.75

3.2

16

2.5

1.95

6.0

2.15

1.6

Extended

Range with

PNP

Figure 6. Power Supply Output Voltage Range

Comparison for Programmable Precision References

Figure 5 illustrates an additional 1.0 uF capacitor, C3,

which is required for normal operation of the NCP100.

Bandwidth concerns are raised when a capacitor is placed

from the cathode to anode of the precision reference. Since

the PNP transistor is used to drive the optocoupler, the

cathode current of the NCP100 is amplified by the beta of the

transistor therefore minimizing the effects of C3. R3 is a

factor in the overall gain of the feedback network and R4

limits the current into the diode of the optocoupler. The

roll–off frequency of the feedback network is related to R1

and C2 only. Figure 7 shows the circuit schematic, the gain

and the phase of the TLV431 and the NCP100 with and

without the PNP.

R1

U1

R2

C2

GND

R3

R1

C3

Q1

U1

R2

C2

GND

R3

R4

C3

Figure 7. Schematics for Gain and Phase Comparison of TLV431 and NCP100

Note: C3 only for NCP100

20

0

30

–10

10

–20

40

40

70

60

Figure 8. TLV431 with PNP

50

Figure 9. TLV431 without PNP

Gain

Phase

Gain

Phase

–30

180

90

0

–90

–180

180

90

0

–90

–180

10

100

1 k

10 k

100 k

Frequency (Hz)

10

100

1 k

10 k

100 k

Frequency (Hz)