HCPL4562 HP [Agilent(Hewlett-Packard)], HCPL4562 Datasheet - Page 17

• Manufacturer Part Number: HCPL4562
• Description: High Bandwidth, Analog/Video Optocouplers
• Manufacturer: HP [Agilent(Hewlett-Packard)]

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
circuit in Figure 4 is used, then potentiometer R4
should be adjusted appropriately.
Design Considerations of the
Application Circuit
The application 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, first select R
desired LED quiescent current by:
For a constant value V
(adjusting the gain with R
keeping the modulation factor (MF) dependent only
on V
Modulation
Factor (MF): ––––– = –––––
For a given G
vary only with h
V
Where:
and,
I
i
––––
O
I
I
Fp-p
i
FQ
PBQ
BXQ
I
Fp-p
p-p
FQ
= V
p-p
E
.
––
CC
V
R
V
––––––––
––––––––––
V
E
G
4
IN
––––– = –––––
CC
– V
i
FQ
V
R
I
PBp-p
R
/R
PBQ
6
V
7
, from 6 mA to 10 mA. If the application
– 2 V
p-p
BE
–––––––––––––
4
R
E
h
( I
V
R
i
2 I
9
FEX
4
, V
F(p-p)
10
G
PB
– ––– [V
FEX
(p-p)
FQ
BE
E
V
R
/ I
V
, and V
R
V
.
INp-p
10
V
9
E
F
E
p-p
) R
R
INp-p
V
2 V
10
INp-p
BEX
7
CC
R
4
p-p
, the circuit topology
E
) preserves linearity by
9
, DC output voltage will
– (I
PBQ
1
to set V
– I
BXQ
E
) R
for the
7
]
(5)
(1)
(3)
(4)
(6)
(7)
(2)
Figure 15 shows the dependency of the DC output
voltage on h
For 9 V < V
that
The voltage gain of the second stage (Q
approximately equal to:
Increasing R
combination of R
reducing R
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
Figure 16), in which case R
set I
Finally, adjust R
gain.
where typically –––– = 0.0032
Definition:
V
i
V
C
PBp-p
h
I
i
I
I
––– * –––––––––––––––––––––––––
R
G
INp-p
R
Fp-p
PBQ
BEX
BXQ
CQ4
FEX
CQ
I
G
f
10
V
Q4
V
FQ
T
9
E
V
CQ4
4
3
= Quiescent LED forward current
= Peak-to-peak small signal LED forward
= Quiescent base photo current
= Base-Emitter voltage of HCPL-4562/
= Quiescent base current of HCPL-4562/
= Current Gain (I
= Voltage across emitter degeneration
= Effective capacitance from collector of Q
= Voltage Gain
= Peak-to-peak small signal
= Unity gain frequency of Q
= Peak-to-peak small signal input voltage
––––
V
1 + s R
V
OUT
–––
R
IN
current
base photo current
HCNW4562 transistor
HCNW4562 transistor
HCNW4562 transistor
resistor R
to ground
V
11
O
2 mA.
9
CC
FEX
(keeping R
11
–––– ––––––
< 12 V, select the value of R
9
––––––
4.25 V
I
470
(R
.
I
PB
4
F
C
11
to achieve the desired voltage
I
11
I
CQ
PB
4
F
and the load impedance) or
R
R
includes the parallel
3
1
4
7
+ –––––––––
R
R
9
10
C
9
9.0 mA
/R
2 R
/I
10
B
) of HCPL-4562/
11
1
ratio constant) will
11
can be increased to
f
T4
4
5
3
) is
11
such
5
1-401
(10)
in
(8)
(9)
3