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, IFQ, 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 R1 to set VE for the desired
LED quiescent current by:
Figure 15 shows the dependency of the DC output
voltage on hFEX.
For 9 V < VCC < 12 V, select the value of R11 such that
VEGVVER10
IF Q = � (1)
R4(�IPB /�IF) R7R9
iF p-p �VIN/R 4( 2)
iF p-p iPB p-p VINp-p
�= (3)
IF Q IP B Q VE
iF(p-p) VINp-p
F actor ( MF ) : = ( 4)
2 IF Q 2 VE
R9
VO= VCC – VB E [V B E X - ( IPB Q - IB X Q) R 7] (5)
R10
GVVER10
IPB Q �( 6)
R7R9
VCC - 2 VB E
IB X Q �( 7)
R6hF E X
VO4.25 V
ICQ4 � � � 9.0 mA (8)
R11 470
R91
*(9)
R10 1
1 + s R 9CCQ 2�R�
11 fT 4
VOUT �IPB R7R9
GV� � (10)
VIN �IFR4R10
�IPB
where typically �IF
p-p
4
( p-p)
p-p
p-p p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
VEGVVER10
IF Q = � (1)
R4(�IPB /�IF) R7R9
iF p-p �VIN/R 4( 2)
iF p-p iPB p-p VINp-p
�= (3)
IF Q IP B Q VE
iF(p-p) VINp-p
F actor ( MF ) : = ( 4)
2 IF Q 2 VE
R9
VO= VCC – VB E [V B E X - ( IPB Q - IB X Q) R 7] (5)
R10
GVVER10
IPB Q �( 6)
R7R9
VCC - 2 VB E
IB X Q �( 7)
R6hF E X
VO4.25 V
ICQ4 � � � 9.0 mA (8)
R11 470
R91
*(9)
R10 1
1 + s R 9CCQ 2�R�
11 fT 4
VOUT �IPB R7R9
GV� � (10)
VIN �IFR4R10
�IPB
where typically �IF
p-p
4
( p-p)
p-p
p-p p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
VEGVVER10
IF Q = � (1)
R4(�IPB /�IF) R7R9
iF p-p �VIN/R 4( 2)
iF p-p iPB p-p VINp-p
�= (3)
IF Q IP B Q VE
iF(p-p) VINp-p
F actor ( MF ) : = ( 4)
2 IF Q 2 VE
R9
VO= VCC – VB E [V B E X - ( IPB Q - IB X Q) R 7] (5)
R10
GVVER10
IPB Q �( 6)
R7R9
VCC - 2 VB E
IB X Q �( 7)
R6hF E X
VO4.25 V
ICQ4 � � � 9.0 mA (8)
R11 470
R91
*(9)
R10 1
1 + s R 9CCQ 2�R�
11 fT 4
VOUT �IPB R7R9
GV� � (10)
VIN �IFR4R10
�IPB
where typically �IF
p-p
4
( p-p)
p-p
p-p p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
VEGVVER10
IF Q = � (1)
R4(�IPB /�IF) R7R9
iF p-p �VIN/R 4( 2)
iF p-p iPB p-p VINp-p
�= (3)
IF Q IP B Q VE
iF(p-p) VINp-p
F actor ( MF ) : = ( 4)
2 IF Q 2 VE
R9
VO= VCC – VB E [V B E X - ( IPB Q - IB X Q) R 7] (5)
R10
GVVER10
IPB Q �( 6)
R7R9
VCC - 2 VB E
IB X Q �( 7)
R6hF E X
VO4.25 V
ICQ4 � � � 9.0 mA (8)
R11 470
R91
*(9)
R10 1
1 + s R 9CCQ 2�R�
11 fT 4
VOUT �IPB R7R9
GV� � (10)
VIN �IFR4R10
�IPB
where typically �IF
p-p
4
( p-p)
p-p
p-p p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
VEGVVER10
IF Q = � (1)
R4(�IPB /�IF) R7R9
iF p-p �VIN/R 4( 2)
iF p-p iPB p-p VINp-p
�= (3)
IF Q IP B Q VE
iF(p-p) VINp-p
F actor ( MF ) : = ( 4)
2 IF Q 2 VE
R9
VO= VCC – VB E [V B E X - ( IPB Q - IB X Q) R 7] (5)
R10
GVVER10
IPB Q �( 6)
R7R9
VCC - 2 VB E
IB X Q �( 7)
R6hF E X
VO4.25 V
ICQ4 � � � 9.0 mA (8)
R11 470
R91
*(9)
R10 1
1 + s R 9CCQ 2�R�
11 fT 4
VOUT �IPB R7R9
GV� � (10)
VIN �IFR4R10
�IPB
where typically �IF
p-p
4
( p-p)
p-p
p-p p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
VEGVVER10
IF Q = � (1)
R4(�IPB /�IF) R7R9
iF p-p �VIN/R 4( 2)
iF p-p iPB p-p VINp-p
�= (3)
IF Q IP B Q VE
iF(p-p) VINp-p
F actor ( MF ) : = ( 4)
2 IF Q 2 VE
R9
VO= VCC – VB E [V B E X - ( IPB Q - IB X Q) R 7] (5)
R10
GVVER10
IPB Q �( 6)
R7R9
VCC - 2 VB E
IB X Q �( 7)
R6hF E X
VO4.25 V
ICQ4 � � � 9.0 mA (8)
R11 470
R91
*(9)
R10 1
1 + s R 9CCQ 2�R�
11 fT 4
VOUT �IPB R7R9
GV� � (10)
VIN �IFR4R10
�IPB
where typically �IF
p-p
4
( p-p)
p-p
p-p p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
VEGVVER10
IF Q = � (1)
R4(�IPB /�IF) R7R9
iF p-p �VIN/R 4( 2)
iF p-p iPB p-p VINp-p
�= (3)
IF Q IP B Q VE
iF(p-p) VINp-p
F actor ( MF ) : = ( 4)
2 IF Q 2 VE
R9
VO= VCC – VB E [V B E X - ( IPB Q - IB X Q) R 7] (5)
R10
GVVER10
IPB Q �( 6)
R7R9
VCC - 2 VB E
IB X Q �( 7)
R6hF E X
VO4.25 V
ICQ4 � � � 9.0 mA (8)
R11 470
R91
*(9)
R10 1
1 + s R 9CCQ 2�R�
11 fT 4
VOUT �IPB R7R9
GV� � (10)
VIN �IFR4R10
�IPB
where typically �IF
p-p
4
( p-p)
p-p
p-p p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
VEGVVER10
IF Q = � (1)
R4(�IPB /�IF) R7R9
iF p-p �VIN/R 4( 2)
iF p-p iPB p-p VINp-p
�= (3)
IF Q IP B Q VE
iF(p-p) VINp-p
F actor ( MF ) : = ( 4)
2 IF Q 2 VE
R9
VO= VCC – VB E [V B E X - ( IPB Q - IB X Q) R 7] (5)
R10
GVVER10
IPB Q �( 6)
R7R9
VCC - 2 VB E
IB X Q �( 7)
R6hF E X
VO4.25 V
ICQ4 � � � 9.0 mA (8)
R11 470
R91
*(9)
R10 1
1 + s R 9CCQ 2�R�
11 fT 4
VOUT �IPB R7R9
GV� � (10)
VIN �IFR4R10
�IPB
where typically �IF
p-p
4
( p-p)
p-p
p-p p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
VEGVVER10
IF Q = � (1)
R4(�IPB /�IF) R7R9
iF p-p �VIN/R 4( 2)
iF p-p iPB p-p VINp-p
�= (3)
IF Q IP B Q VE
iF(p-p) VINp-p
F actor ( MF ) : = ( 4)
2 IF Q 2 VE
R9
VO= VCC – VB E [V B E X - ( IPB Q - IB X Q) R 7] (5)
R10
GVVER10
IPB Q �( 6)
R7R9
VCC - 2 VB E
IB X Q �( 7)
R6hF E X
VO4.25 V
ICQ4 � � � 9.0 mA (8)
R11 470
R91
*(9)
R10 1
1 + s R 9CCQ 2�R�
11 fT 4
VOUT �IPB R7R9
GV� � (10)
VIN �IFR4R10
�IPB
where typically �IF
p-p
4
( p-p)
p-p
p-p p-p
p-p
Q4
3
4
≈
≈
≈
≈
≈
≈
= 0.0032
–
+
≈
≈
For a constant value VINp-p, the circuit topology
(adjusting the gain with R4) preserves linearity by
keeping the modulation factor (MF) dependent only
on VE.
Modulation
For a given GV, VE, and VCC, DC output voltage will vary
only with hFEX.
Where:
and,
The voltage gain of the second stage (Q3) is
approximately equal to:
Increasing R′11 (R′11 includes the parallel combination of
R11 and the load impedance) or reducing R9 (keeping
R9/R10 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 (Q5 in
Figure 16), in which case R11 can be increased to
set ICQ4 ≅ 2 mA.
Finally, adjust R4 to achieve the desired voltage gain.
Denition:
GV = Voltage Gain
IFQ = Quiescent LED forward current
iFp-p = Peak-to-peak small signal LED forward
current
VINp-p = Peak-to-peak small signal input voltage
iPBp-p = Peak-to-peak small signal
base photo current
IPBQ = Quiescent base photo current
VBEX = Base-Emitter voltage of HCPL-4562/
HCNW4562 transistor
IBXQ = Quiescent base current of HCPL-4562/
HCNW4562 transistor
hFEX = Current Gain (IC/IB) of HCPL-4562/
HCNW4562 transistor
VE = Voltage across emitter degeneration
resistor R4
fT4 = Unity gain frequency of Q5
CCQ3 = Eective capacitance from collector of Q3
to ground