16
Conversion from HCPL-4562 to HCNW4562
In order to obtain similar circuit performance when
converting from the HCPL-4562 to the HCNW4562,
it is recommended to increase the Quiescent Input
Current, I
FQ
, from 6 mA to 10 mA. If the application circuit
in Figure 4 is used, then potentiometer R4 should be
adjusted appropriately.
Design Considerations of the Application Circuit
The appÏication circuit in Figure 4 incorporates
several features that help maximize the bandwidth
performance of the HCPL-4562/HCNW4562. Most
important of these features is peaked response of the
detector circuit that helps extend the frequency range
over which the voltage gain is relatively constant. The
number of gain stages, the overall circuit topology, and
the choice of DC bias points are all consequences of
the desire to maximize bandwidth performance.
To use the circuit, rst select R
1
to set V
E
for the desired
LED quiescent current by:
Figure 15 shows the dependency of the DC output
voltage on h
FEX
.
For 9 V < V
CC
< 12 V, select the value of R
11
such that
V
E
G
V
V
E
R
10
I
F Q
= � (1)
R
4
(� I
PB
/� I
F
) R
7
R
9
i
F p-p
� V
IN
/R
4
(2)
i
F p-p
i
PB p-p
V
INp-p
� = (3)
I
F Q
I
PB Q
V
E
i
F(p-p)
V
INp-p
F actor ( MF ) : = (4)
2 I
F Q
2 V
E
R
9
V
O
= V
CC
– V
B E
[V
B E X
- ( I
PB Q
- I
B XQ
) R
7
] ( 5)
R
10
G
V
V
E
R
10
I
PB Q
� (6)
R
7
R
9
V
CC
- 2 V
B E
I
B XQ
� (7)
R
6
h
F E X
V
O
4.25 V
I
CQ4
� � � 9.0 mA (8)
R
11
470
R
9
1
*
(9)
R
10
1
1 + s R
9
C
CQ
2� R �
11
f
T4
V
OUT
� I
PB
R
7
R
9
G
V
� � (10)
V
IN
� I
F
R
4
R
10
� I
PB
where typically
� I
F
p-p
4
( p-p)
p-p
p-p
p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
V
E
G
V
V
E
R
10
I
F Q
= � (1)
R
4
(� I
PB
/� I
F
) R
7
R
9
i
F p-p
� V
IN
/R
4
(2)
i
F p-p
i
PB p-p
V
INp-p
� = (3)
I
F Q
I
PB Q
V
E
i
F(p-p)
V
INp-p
F actor ( MF ) : = (4)
2 I
F Q
2 V
E
R
9
V
O
= V
CC
– V
B E
[V
B E X
- ( I
PB Q
- I
B XQ
) R
7
] ( 5)
R
10
G
V
V
E
R
10
I
PB Q
� (6)
R
7
R
9
V
CC
- 2 V
B E
I
B XQ
� (7)
R
6
h
F E X
V
O
4.25 V
I
CQ4
� � � 9.0 mA (8)
R
11
470
R
9
1
*
(9)
R
10
1
1 + s R
9
C
CQ
2� R �
11
f
T4
V
OUT
� I
PB
R
7
R
9
G
V
� � (10)
V
IN
� I
F
R
4
R
10
� I
PB
where typically
� I
F
p-p
4
( p-p)
p-p
p-p
p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
V
E
G
V
V
E
R
10
I
F Q
= � (1)
R
4
(� I
PB
/� I
F
) R
7
R
9
i
F p-p
� V
IN
/R
4
(2)
i
F p-p
i
PB p-p
V
INp-p
� = (3)
I
F Q
I
PB Q
V
E
i
F(p-p)
V
INp-p
F actor ( MF ) : = (4)
2 I
F Q
2 V
E
R
9
V
O
= V
CC
– V
B E
[V
B E X
- ( I
PB Q
- I
B XQ
) R
7
] ( 5)
R
10
G
V
V
E
R
10
I
PB Q
� (6)
R
7
R
9
V
CC
- 2 V
B E
I
B XQ
� (7)
R
6
h
F E X
V
O
4.25 V
I
CQ4
� � � 9.0 mA (8)
R
11
470
R
9
1
*
(9)
R
10
1
1 + s R
9
C
CQ
2� R �
11
f
T4
V
OUT
� I
PB
R
7
R
9
G
V
� � (10)
V
IN
� I
F
R
4
R
10
� I
PB
where typically
� I
F
p-p
4
( p-p)
p-p
p-p
p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
V
E
G
V
V
E
R
10
I
F Q
= � (1)
R
4
(� I
PB
/� I
F
) R
7
R
9
i
F p-p
� V
IN
/R
4
(2)
i
F p-p
i
PB p-p
V
INp-p
� = (3)
I
F Q
I
PB Q
V
E
i
F(p-p)
V
INp-p
F actor ( MF ) : = (4)
2 I
F Q
2 V
E
R
9
V
O
= V
CC
– V
B E
[V
B E X
- ( I
PB Q
- I
B XQ
) R
7
] ( 5)
R
10
G
V
V
E
R
10
I
PB Q
� (6)
R
7
R
9
V
CC
- 2 V
B E
I
B XQ
� (7)
R
6
h
F E X
V
O
4.25 V
I
CQ4
� � � 9.0 mA (8)
R
11
470
R
9
1
*
(9)
R
10
1
1 + s R
9
C
CQ
2� R �
11
f
T4
V
OUT
� I
PB
R
7
R
9
G
V
� � (10)
V
IN
� I
F
R
4
R
10
� I
PB
where typically
� I
F
p-p
4
( p-p)
p-p
p-p
p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
V
E
G
V
V
E
R
10
I
F Q
= � (1)
R
4
(� I
PB
/� I
F
) R
7
R
9
i
F p-p
� V
IN
/R
4
(2)
i
F p-p
i
PB p-p
V
INp-p
� = (3)
I
F Q
I
PB Q
V
E
i
F(p-p)
V
INp-p
F actor ( MF ) : = (4)
2 I
F Q
2 V
E
R
9
V
O
= V
CC
– V
B E
[V
B E X
- ( I
PB Q
- I
B XQ
) R
7
] ( 5)
R
10
G
V
V
E
R
10
I
PB Q
� (6)
R
7
R
9
V
CC
- 2 V
B E
I
B XQ
� (7)
R
6
h
F E X
V
O
4.25 V
I
CQ4
� � � 9.0 mA (8)
R
11
470
R
9
1
*
(9)
R
10
1
1 + s R
9
C
CQ
2� R �
11
f
T4
V
OUT
� I
PB
R
7
R
9
G
V
� � (10)
V
IN
� I
F
R
4
R
10
� I
PB
where typically
� I
F
p-p
4
( p-p)
p-p
p-p
p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
V
E
G
V
V
E
R
10
I
F Q
= � (1)
R
4
(� I
PB
/� I
F
) R
7
R
9
i
F p-p
� V
IN
/R
4
(2)
i
F p-p
i
PB p-p
V
INp-p
� = (3)
I
F Q
I
PB Q
V
E
i
F(p-p)
V
INp-p
F actor ( MF ) : = (4)
2 I
F Q
2 V
E
R
9
V
O
= V
CC
– V
B E
[V
B E X
- ( I
PB Q
- I
B XQ
) R
7
] ( 5)
R
10
G
V
V
E
R
10
I
PB Q
� (6)
R
7
R
9
V
CC
- 2 V
B E
I
B XQ
� (7)
R
6
h
F E X
V
O
4.25 V
I
CQ4
� � � 9.0 mA (8)
R
11
470
R
9
1
*
(9)
R
10
1
1 + s R
9
C
CQ
2� R �
11
f
T4
V
OUT
� I
PB
R
7
R
9
G
V
� � (10)
V
IN
� I
F
R
4
R
10
� I
PB
where typically
� I
F
p-p
4
( p-p)
p-p
p-p
p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
V
E
G
V
V
E
R
10
I
F Q
= � (1)
R
4
(� I
PB
/� I
F
) R
7
R
9
i
F p-p
� V
IN
/R
4
(2)
i
F p-p
i
PB p-p
V
INp-p
� = (3)
I
F Q
I
PB Q
V
E
i
F(p-p)
V
INp-p
F actor ( MF ) : = (4)
2 I
F Q
2 V
E
R
9
V
O
= V
CC
– V
B E
[V
B E X
- ( I
PB Q
- I
B XQ
) R
7
] ( 5)
R
10
G
V
V
E
R
10
I
PB Q
� (6)
R
7
R
9
V
CC
- 2 V
B E
I
B XQ
� (7)
R
6
h
F E X
V
O
4.25 V
I
CQ4
� � � 9.0 mA (8)
R
11
470
R
9
1
*
(9)
R
10
1
1 + s R
9
C
CQ
2� R �
11
f
T4
V
OUT
� I
PB
R
7
R
9
G
V
� � (10)
V
IN
� I
F
R
4
R
10
� I
PB
where typically
� I
F
p-p
4
( p-p)
p-p
p-p
p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
V
E
G
V
V
E
R
10
I
F Q
= � (1)
R
4
(� I
PB
/� I
F
) R
7
R
9
i
F p-p
� V
IN
/R
4
(2)
i
F p-p
i
PB p-p
V
INp-p
� = (3)
I
F Q
I
PB Q
V
E
i
F(p-p)
V
INp-p
F actor ( MF ) : = (4)
2 I
F Q
2 V
E
R
9
V
O
= V
CC
– V
B E
[V
B E X
- ( I
PB Q
- I
B XQ
) R
7
] ( 5)
R
10
G
V
V
E
R
10
I
PB Q
� (6)
R
7
R
9
V
CC
- 2 V
B E
I
B XQ
� (7)
R
6
h
F E X
V
O
4.25 V
I
CQ4
� � � 9.0 mA (8)
R
11
470
R
9
1
*
(9)
R
10
1
1 + s R
9
C
CQ
2� R �
11
f
T4
V
OUT
� I
PB
R
7
R
9
G
V
� � (10)
V
IN
� I
F
R
4
R
10
� I
PB
where typically
� I
F
p-p
4
( p-p)
p-p
p-p
p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
V
E
G
V
V
E
R
10
I
F Q
= � (1)
R
4
(� I
PB
/� I
F
) R
7
R
9
i
F p-p
� V
IN
/R
4
(2)
i
F p-p
i
PB p-p
V
INp-p
� = (3)
I
F Q
I
PB Q
V
E
i
F(p-p)
V
INp-p
F actor ( MF ) : = (4)
2 I
F Q
2 V
E
R
9
V
O
= V
CC
– V
B E
[V
B E X
- ( I
PB Q
- I
B XQ
) R
7
] ( 5)
R
10
G
V
V
E
R
10
I
PB Q
� (6)
R
7
R
9
V
CC
- 2 V
B E
I
B XQ
� (7)
R
6
h
F E X
V
O
4.25 V
I
CQ4
� � � 9.0 mA (8)
R
11
470
R
9
1
*
(9)
R
10
1
1 + s R
9
C
CQ
2� R �
11
f
T4
V
OUT
� I
PB
R
7
R
9
G
V
� � (10)
V
IN
� I
F
R
4
R
10
� I
PB
where typically
� I
F
p-p
4
( p-p)
p-p
p-p
p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
For a constant value V
INp-p
, the circuit topology
(adjusting the gain with R
4
) preserves linearity by
keeping the modulation factor (MF) dependent only
on V
E
.
Modulation
For a given G
V
, V
E
, and V
CC
, DC output voltage will vary
only with h
FEX
.
Where:
and,
The voltage gain of the second stage (Q
3
) is
approximately equal to:
Increasing R′
11
(R′
11
includes the parallel combination of
R
11
and the load impedance) or reducing R
9
(keeping
R
9
/R
10
ratio constant) will improve the bandwidth.
If it is necessary to drive a low impedance load,
bandwidth may also be preserved by adding an
additional emitter following the buffer stage (Q
5
in
Figure 16), in which case R
11
can be increased to
set I
CQ4
≅ 2 mA.
Finally, adjust R
4
to achieve the desired voltage gain.
Denition:
G
V
= Voltage Gain
I
FQ
= Quiescent LED forward current
i
F
p-p
= Peak-to-peak small signal LED forward
current
V
IN
p-p
= Peak-to-peak small signal input voltage
i
PB
p-p
= Peak-to-peak small signal
base photo current
I
PBQ
= Quiescent base photo current
V
BEX
= Base-Emitter voltage of HCPL-4562/
HCNW4562 transistor
I
BXQ
= Quiescent base current of HCPL-4562/
HCNW4562 transistor
h
FEX
= Current Gain (I
C
/I
B
) of HCPL-4562/
HCNW4562 transistor
V
E
= Voltage across emitter degeneration
resistor R
4
f
T
4
= Unity gain frequency of Q
5
C
CQ
3
= Eective capacitance from collector of Q
3
to ground
