HP HCPL-2602 High cmr line receiver optocoupler Datasheet

High CMR Line Receiver
Optocouplers
Technical Data
HCPL-2602
HCPL-2612
Features
Applications
Description
• 1000 V/µs Minimum Common
Mode Rejection (CMR) at
VCM = 50 V for HCPL-2602
and 3.5 kV/µs Minimum
CMR at VCM = 300 V for
HCPL-2612
• Line Termination Included –
No Extra Circuitry Required
• Accepts a Broad Range of
Drive Conditions
• LED Protection Minimizes
LED Efficiency Degradation
• High Speed: 10 MBd
(Limited by Transmission
Line in Many Applications)
• Guaranteed AC and DC
Performance over
Temperature: 0°C to 70°C
• External Base Lead Allows
“LED Peaking” and LED
Current Adjustment
• Safety Approval
UL Recognized – 2500 V rms
for 1 Minute
CSA Approved
• MIL-STD-1772 Version
Available (HCPL-1930/1)
• Isolated Line Receiver
• Computer-Peripheral
Interface
• Microprocessor System
Interface
• Digital Isolation for A/D,
D/A Conversion
• Current Sensing
• Instrument Input/Output
Isolation
• Ground Loop Elimination
• Pulse Transformer
Replacement
• Power Transistor Isolation
in Motor Drives
The HCPL-2602/12 are optically
coupled line receivers that
combine a GaAsP light emitting
diode, an input current regulator
and an integrated high gain photo
detector. The input regulator
serves as a line termination for
line receiver applications. It
clamps the line voltage and
regulates the LED current so line
reflections do not interfere with
circuit performance.
The regulator allows a typical
LED current of 8.5 mA before it
starts to shunt excess current.
The output of the detector IC is
Functional Diagram
NC
1
8
VCC
IN+
2
7
VE
IN–
3
6
VO
CATHODE
4
5
GND
SHIELD
TRUTH TABLE
(POSITIVE LOGIC)
LED
ON
OFF
ON
OFF
ON
OFF
ENABLE
H
H
L
L
NC
NC
OUTPUT
L
H
H
H
L
H
A 0.1 µF bypass capacitor must be connected between pins 5 and 8.
CAUTION: It is advised that normal static precautions be taken in handling and assembly of this component to
prevent damage and/or degradation which may be induced by ESD.
1-314
5965-3585E
an open collector Schottky
clamped transistor. An enable
input gates the detector. The
internal detector shield provides a
guaranteed common mode
transient immunity specification
of 1000 V/µs for the 2602, and
3500 V/µs for the 2612.
DC specifications are defined
similar to TTL logic. The
optocoupler ac and dc operational
parameters are guaranteed from
0°C to 70°C allowing trouble-free
interfacing with digital logic
circuits. An input current of 5 mA
will sink an eight gate fan-out
(TTL) at the output.
The HCPL-2602/12 are useful as
line receivers in high noise
environments that conventional
line receivers cannot tolerate. The
higher LED threshold voltage
provides improved immunity to
differential noise and the internally
shielded detector provides orders
of magnitude improvement in
common mode rejection with little
or no sacrifice in speed.
Selection Guide
Minimum CMR
dV/dt
(V/µs)
VCM
(V)
Input
OnCurrent
(mA)
NA
NA
5
8-Pin DIP (300 Mil)
Output
Enable
Single
Channel
Package
YES
6N137
NO
5,000
50
YES
10,000
1,000
YES
HCPL-2631
3,500
300
1,000
50
1,000[2]
1,000
3
YES
HCPL-2612[1]
YES
HCPL-261A
NO
YES
NO
1,000
50
12.5
Hermetic
Single
Channel
Package
Single and
Dual Channel
Packages
HCNW137
HCNW2601
HCPL-0631
HCPL-0611
HCPL-4661
HCPL-2602[1]
Widebody
(400 Mil)
HCPL-0630
HCPL-0601
HCPL-2611
YES
Dual
Channel
Package
HCPL-0600
HCPL-2601
NO
50
Single
Channel
Package
HCPL-2630
NO
1,000
Dual
Channel
Package
Small-Outline SO-8
HCNW2611
HCPL-0661
HCPL-061A
HCPL-263A
HCPL-261N
HCPL-063A
HCPL-061N
HCPL-263N
[3]
HCPL-063N
HCPL-193X
HCPL-56XX
HCPL-66XX
Notes:
1. HCPL-2602/2612 devices include input current regulator.
2. 15 kV/µs with VCM = 1 kV can be achieved using HP application circuit.
3. Enable is available for single channel products only, except for HCPL-193X devices.
1-315
Ordering Information
Specify Part Number followed by Option Number (if desired).
Example:
HCPL-2602#XXX
300 = Gull Wing Surface Mount Option
500 = Tape and Reel Packaging Option
Option data sheets available. Contact your Hewlett-Packard sales representative or authorized distributor for
information.
Schematic
+
II
2
IF
ICC
8
IO
6
VCC
VO
VI
–
3
90 Ω
SHIELD
IE
5
7
VE
4
USE OF A 0.1 µF BYPASS CAPACITOR CONNECTED
BETWEEN PINS 5 AND 8 IS REQUIRED (SEE NOTE 1).
1-316
GND
Package Outline Drawings
8-Pin DIP Package
7.62 ± 0.25
(0.300 ± 0.010)
9.65 ± 0.25
(0.380 ± 0.010)
8
7
6
5
6.35 ± 0.25
(0.250 ± 0.010)
TYPE NUMBER
DATE CODE
HP XXXX
YYWW RU
1
2
3
4
UL
RECOGNITION
1.78 (0.070) MAX.
1.19 (0.047) MAX.
5° TYP.
4.70 (0.185) MAX.
+ 0.076
0.254 - 0.051
+ 0.003)
(0.010 - 0.002)
0.51 (0.020) MIN.
2.92 (0.115) MIN.
0.65 (0.025) MAX.
1.080 ± 0.320
(0.043 ± 0.013)
2.54 ± 0.25
(0.100 ± 0.010)
DIMENSIONS IN MILLIMETERS AND (INCHES).
8-Pin DIP Package with Gull Wing Surface Mount Option 300
PAD LOCATION (FOR REFERENCE ONLY)
9.65 ± 0.25
(0.380 ± 0.010)
8
7
6
1.016 (0.040)
1.194 (0.047)
5
4.826 TYP.
(0.190)
6.350 ± 0.25
(0.250 ± 0.010)
1
2
3
9.398 (0.370)
9.906 (0.390)
4
1.194 (0.047)
1.778 (0.070)
1.19
(0.047)
MAX.
1.780
(0.070)
MAX.
9.65 ± 0.25
(0.380 ± 0.010)
7.62 ± 0.25
(0.300 ± 0.010)
4.19 MAX.
(0.165)
1.080 ± 0.320
(0.043 ± 0.013)
0.635 ± 0.130
2.54
(0.025 ± 0.005)
(0.100)
BSC
DIMENSIONS IN MILLIMETERS (INCHES).
LEAD COPLANARITY = 0.10 mm (0.004 INCHES).
0.381 (0.015)
0.635 (0.025)
0.635 ± 0.25
(0.025 ± 0.010)
+ 0.076
0.254 - 0.051
+ 0.003)
(0.010 - 0.002)
12° NOM.
1-317
TEMPERATURE – °C
Solder Reflow Temperature Profile (Gull Wing Surface Mount Option 300 Parts)
260
240
220
200
180
160
140
120
100
80
∆T = 145°C, 1°C/SEC
∆T = 115°C, 0.3°C/SEC
∆T = 100°C, 1.5°C/SEC
60
40
20
0
0
1
2
3
4
5
6
7
8
9
10
11
12
TIME – MINUTES
Note: Use of nonchlorine activated fluxes is highly recommended.
Regulatory Information
The HCPL-2602/2612 have been
approved by the following
organizations:
UL
Recognized under UL 1577,
Component Recognition
Program, File E55361.
CSA
Approved under CSA Component
Acceptance Notice #5, File CA
88324.
Insulation and Safety Related Specifications
Parameter
Min. External Air Gap
(External Clearance)
Min. External Tracking
Path (External Creepage)
Min. Internal Plastic
Gap (Internal Clearance)
Tracking Resistance
(Comparative Tracking
Index)
Isolation Group
Symbol
L(I01)
Value
7.1
Units
mm
L(I02)
7.4
mm
0.08
mm
200
V
CTI
IIIa
Conditions
Measured from input terminals to output terminals,
shortest distance through air.
Measured from input terminals to output terminals,
shortest distance path along body.
Through insulation distance, conductor to conductor,
usually the direct distance between the photoemitter
and photodetector inside the optocoupler cavity.
DIN IEC 112/VDE 0303 Part 1
Material Group (DIN VDE 0110, 1/89, Table 1)
Option 300 - surface mount classification is Class A in accordance with CECC 00802.
1-318
Absolute Maximum Ratings (No Derating Required up to 85°C)
Parameter
Storage Temperature
Operating Temperature
Forward Input Current
Reverse Input Current
Input Current, Pin 4
Supply Voltage (1 Minute Maximum)
Enable Input Voltage (Not to Exceed VCC by
more than 500 mV)
Output Collector Current
Output Collector Voltage (Selection for Higher
Output Voltages up to 20 V is Available.)
Output Collector Power Dissipation
Lead Solder Temperature
Symbol
TS
TA
II
IIR
Min.
-55
-40
VCC
VE
Max.
125
85
60
60
10
7
VCC + 0.5
Units
°C
°C
mA
mA
mA
V
V
IO
VO
50
7
mA
V
PO
TLS
40
mW
260°C for 10 sec., 1.6 mm below
seating plane
See Package Outline Drawings section
-10
Solder Reflow Temperature Profile
Recommended Operating Conditions
Parameter
Symbol
Min.
Max.
Units
Input Current, Low Level
IIL
0
250
µA
Input Current, High Level
IIH
5*
60
mA
Supply Voltage, Output
VCC
4.5
5.5
V
High Level Enable Voltage
VEH
2.0
VCC
V
Low Level Enable Voltage
VEL
0
0.8
V
5
TTL Loads
Fan Out (@ RL = 1 kΩ)
N
Output Pull-up Resistor
RL
330
4K
Ω
Operating Temperature
TA
0
70
°C
*The initial switching threshold is 5 mA or less. It is recommended that an input current
between 6.3 mA and 10 mA be used to obtain best performance and to provide at least
20% LED degradation guardband.
1-319
Electrical Characteristics
Over recommended temperature (TA = 0°C to +70°C) unless otherwise specified. See note 1.
Parameter
Sym.
High Level Output
Current
Min.
Typ.*
Max.
Units
IOH
5.5
100
µA
VCC = 5.5 V, VO = 5.5 V,
II = 250 µA, VE = 2.0 V
1
Low Level Output
Voltage
VOL
0.35
0.6
V
VCC = 5.5 V, II = 5 mA,
VE = 2.0 V,
IOL (Sinking) = 13 mA
2, 4,
5, 14
High Level Supply
Current
ICCH
7.5
10
mA
VCC = 5.5 V, II = 0 mA,
VE = 0.5 V
Low Level Supply
Current
ICCL
10
13
mA
VCC = 5.5 V, II = 60 mA,
VE = 0.5 V
High Level Enable
Current
IEH
-0.7
-1.6
mA
VCC = 5.5 V, VE = 2.0 V
Low Level Enable
Current
IEL
-0.9
-1.6
mA
VCC = 5.5 V, VE = 0.5 V
High Level Enable
Voltage
VEH
Low Level Enable
Voltage
VEL
2.0
0.8
V
2.3
2.7
0.95
Input Reverse
Voltage
VR
0.75
Input Capacitance
CIN
90
1-320
Note
10
V
2.4
VI
*All typicals at VCC = 5 V, TA = 25°C.
Fig.
V
2.0
Input Voltage
Test Conditions
II = 5 mA
II = 60 mA
V
IR = 5 mA
pF
VI = 0 V, f = 1 MHz
3
Switching Specifications
Over recommended temperature (TA = 0°C to +70°C), VCC = 5 V, II = 7.5 mA, unless otherwise specified.
Parameter
Symbol
Propagation Delay
Time to High Output
Level
tPLH
Propagation Delay
Time to Low Output
Level
tPHL
Pulse Width
Distortion
Device
Min.
20
25
|tPHL-tPLH|
Typ.*
Max.
Units
75
ns
100
ns
75
ns
100
ns
35
ns
40
ns
Test Conditions
48
Note
6, 7, 8
3
6, 7, 8
4
9
13
TA = 25°C
50
3.5
Fig.
TA = 25°C
RL = 350 Ω
CL = 15 pF
12,
13
Propagation Delay
Skew
tPSK
Output Rise Time
(10-90%)
tr
24
ns
12
Output Fall Time
(90-10%)
tf
10
ns
12
Propagation Delay
Time of Enable from
VEH to VEL
tELH
30
ns
Propagation Delay
Time of Enable from
VEL to VEH
tEHL
Common Mode
Transient
Immunity at High
Output Level
|CMH|
Common Mode
Transient
Immunity at Low
Output Level
|CML|
20
HCPL-2602
ns
1000 10,000
RL = 350 Ω, CL = 15 pF,
VEL = 0 V, VEH = 3 V
10, 11
5
RL = 350 Ω, CL = 15 pF,
VEL = 0 V, VEH = 3 V
10, 11
6
13
7, 9,
10
13
8, 9
10
VCM = 50 V
V/µs
HCPL-2612
3500 15,000
HCPL-2602
1000 10,000
VCM = 300 V
VCM = 50 V
V/µs
HCPL-2612
3500 15,000
VCM = 300 V
VO(MIN) = 2 V,
RL = 350 Ω,
II = 0 mA,
TA = 25°C
VO(MAX) = 0.8 V,
RL = 350 Ω,
II = 7.5 mA,
TA = 25°C
*All typicals at VCC = 5 V, TA = 25°C.
Package Characteristics
All Typicals at TA = 25°C
Parameter
Input-Output Momentary
Withstand Voltage*
Input-Output Resistance
Input-Output Capacitance
Sym.
VISO
RI-O
CI-O
Min.
2500
Typ.
1012
0.6
Max.
Units
V rms
Ω
pF
Test Conditions
RH ≤ 50%, t = 1 min.,
TA = 25°C
VI-O = 500 Vdc
f = 1 MHz
Fig.
Note
2, 11
2
2
*The Input-Output Momentary Withstand Voltage is a dielectric voltage rating that should not be interpreted as an input-output
continuous voltage rating. For the continuous voltage rating refer to the VDE 0884 Insulation Characteristics Table (if applicable),
your equipment level safety specification or HP Application Note 1074 entitled “Optocoupler Input-Output Endurance Voltage.”
1-321
VCC = 5.5 V
VO = 5.5 V
VE = 2 V
II = 250 µA
10
5
0
-60 -40 -20
0
20
40
60
80 100
IO = 12.8 mA
0.3
RL = 350 Ω
3
RL = 1 KΩ
2
RL = 4 KΩ
1
1
2
3
4
5
6
IF – FORWARD INPUT CURRENT – mA
Figure 4. Typical Output Voltage vs.
Forward Input Current.
1-322
IOL – LOW LEVEL OUTPUT CURRENT – mA
VO – OUTPUT VOLTAGE – V
VCC = 5 V
TA = 25 °C
0
IO = 6.4 mA
0.2
IO = 9.6 mA
0.1
-60 -40 -20
0°C
2.2
25°C
70°C
2.0
1.8
1.6
1.4
1.2
0
20
40
60
80 100
70
VCC = 5 V
VE = 2 V
VOL = 0.6 V
60
II = 10-15 mA
50
II = 5.0 mA
40
20
-60 -40 -20
2.4
1.0
Figure 2. Typical Low Level Output
Voltage vs. Temperature.
6
0
IO = 16 mA
TA – TEMPERATURE – °C
Figure 1. Typical High Level Output
Current vs. Temperature.
4
VCC = 5.5 V
VE = 2 V
II = 5 mA
0.4
TA – TEMPERATURE – °C
5
2.6
0.5
VI – INPUT VOLTAGE – V
15
VOL – LOW LEVEL OUTPUT VOLTAGE – V
IOH – HIGH LEVEL OUTPUT CURRENT – µA
Notes:
1. Bypassing of the power supply line is required, with a 0.1 µF ceramic disc capacitor adjacent to each optocoupler as illustrated in
Figure 15. Total lead length between both ends of the capacitor and the isolator pins should not exceed 20 mm.
2. Device considered a two terminal device: pins 1, 2, 3, and 4 shorted together, and pins 5, 6, 7, and 8 shorted together.
3. The tPLH propagation delay is measured from the 3.75 mA point on the falling edge of the input pulse to the 1.5 V point on the rising
edge of the output pulse.
4. The tPHL propagation delay is measured from the 3.75 mA point on the rising edge of the input pulse to the 1.5 V point on the falling
edge of the output pulse.
5. The tELH enable propagation delay is measured from the 1.5 V point on the falling edge of the enable input pulse to the 1.5 V point
on the rising edge of the output pulse.
6. The tEHL enable propagation delay is measured from the 1.5 V point on the rising edge of the enable input pulse to the 1.5 V point on
the falling edge of the output pulse.
7. CMH is the maximum tolerable rate of rise of the common mode voltage to assure that the output will remain in a high logic state
(i.e., VOUT > 2.0 V).
8. CML is the maximum tolerable rate of fall of the common mode voltage to assure that the output will remain in a low logic state (i.e.,
VOUT < 0.8 V).
9. For sinusoidal voltages,
|dvCM|
––––––
= πfCMVCM (p-p)
dt max
10. No external pull up is required for a high logic state on the enable input. If the VE pin is not used, tying VE to VCC will result in
improved CMR performance.
11. In accordance with UL 1577, each optocoupler is proof tested by applying an insulation test voltage of ≥ 3000 for one second
(leakage detection current limit, Ii-o ≤ 5 µA).
12. tPSK is equal to the worst case difference in tPHL and/or tPLH that will be seen between units at any given temperature within the
operating condition range.
13. See application section titled “Propagation Delay, Pulse-Width Distortion and Propagation Delay Skew” for more information.
0
20
40
60
80 100
TA – TEMPERATURE – °C
Figure 5. Typical Low Level Output
Current vs. Temperature.
0
10
20
30
40
50
60
II – INPUT CURRENT – mA
Figure 3. Typical Input Characteristics.
+5 V
INPUT
MONITORING
NODE
1
VCC 8
2
7
3
6
0.1µF
BYPASS
RL
OUTPUT VO
MONITORING
NODE
*CL
RM
4
GND
100
tP – PROPAGATION DELAY – ns
II
PULSE GEN.
Z O = 50 Ω
t f = t r = 5 ns
5
*CL IS APPROXIMATELY 15 pF WHICH INCLUDES
PROBE AND STRAY WIRING CAPACITANCE.
I I = 7.50 mA
INPUT
II
I I = 3.75 mA
t PHL
t PLH
PWD – PULSE WIDTH DISTORTION – ns
tP – PROPAGATION DELAY – ns
tPLH , RL = 4 KΩ
75
tPLH , RL = 350 Ω
tPLH , RL = 1 KΩ
45
30
tPHL , RL = 350 Ω
1 KΩ
4 KΩ
5
9
7
11
13
20
tPLH , RL = 350 Ω
0
20
40
60
80 100
TA – TEMPERATURE – °C
15
40
RL = 4 kΩ
30
VCC = 5 V
II = 7.5 mA
20
RL = 350 kΩ
10
0
RL = 1 kΩ
-10
-60 -40 -20
II – PULSE INPUT CURRENT – mA
0
20
40
60
80 100
TA – TEMPERATURE – °C
Figure 8. Typical Propagation Delay
vs. Pulse Input Current.
PULSE GEN.
Z O = 50 Ω
t f = t r = 5 ns
tPLH , RL = 1 KΩ
40
Figure 7. Typical Propagation Delay
vs. Temperature.
VCC = 5 V
TA = 25°C
90
tPLH , RL = 4 KΩ
tPHL , RL = 350 Ω
1 KΩ
60
4 KΩ
1.5 V
Figure 6. Test Circuit for tPHL and tPLH.
60
80
0
-60 -40 -20
OUTPUT
VO
105
VCC = 5 V
II = 7.5 mA
Figure 9. Typical Pulse Width
Distortion vs. Temperature.
INPUT VE
MONITORING NODE
+5 V
VCC 8
2
7
3
6
0.1 µF
R
BYPASS L
*CL
4
GND
5
*CL IS APPROXIMATELY 15 pF WHICH INCLUDES
PROBE AND STRAY WIRING CAPACITANCE.
3.0 V
INPUT
VE
1.5 V
t EHL
OUTPUT
VO
Figure 10. Test Circuit for tEHL and tELH.
t ELH
1.5 V
OUTPUT VO
MONITORING
NODE
tE – ENABLE PROPAGATION DELAY – ns
7.5 mA
II
1
120
VCC = 5 V
VEH = 3 V
VEL = 0 V
90 II = 7.5 mA
tELH, RL = 4 kΩ
60
tELH, RL = 1 kΩ
30
tELH, RL = 350 Ω
tEHL, RL = 350 Ω, 1 kΩ, 4 kΩ
0
-60 -40 -20 0 20 40 60 80 100
TA – TEMPERATURE – °C
Figure 11. Typical Enable Propagation
Delay vs. Temperature.
1-323
tr, tf – RISE, FALL TIME – ns
II
VCC = 5 V
II = 7.5 mA
tRISE
tFALL
A
RL = 4 kΩ
300
1
VCC 8
2
7
3
6
+5 V
B
290
60
4
RL = 1 kΩ
40
GND
0.1 µF
BYPASS
350 Ω
OUTPUT VO
MONITORING
NODE
5
VCM
+
–
PULSE
GENERATOR
Z O = 50 Ω
RL = 350 Ω
20
0
-60 -40 -20
RL = 350 Ω, 1 kΩ, 4 kΩ
0 20 40 60 80 100
VCM (PEAK)
TA – TEMPERATURE – °C
VCM
Figure 12. Typical Rise and Fall Time
vs. Temperature.
VO
0V
5V
VO
SWITCH AT A: II = 0 mA
CMH
VO (MIN.)
SWITCH AT B: II = 7.5 mA
VO (MAX.)
0.5 V
CML
Figure 13. Test Circuit for Common Mode Transient Immunity and Typical
Waveforms.
ITH – INPUT THRESHOLD CURRENT – mA
GND BUS (BACK)
VCC = 5.0 V
VO = 0.6 V
5
VCC BUS (FRONT)
NC
4
3
0.1µF
ENABLE
(IF USED)
RL = 350 Ω
2
NC
RL = 1 kΩ
1
RL = 4 kΩ
0
-60 -40 -20
0
OUTPUT 1
NC
20
40
60
80 100
0.1µF
ENABLE
(IF USED)
TA – TEMPERATURE – °C
NC
OUTPUT 2
Figure 14. Typical Input Threshold
Current vs. Temperature.
10 mm MAX.
(SEE NOTE 1)
Figure 15. Recommended Printed Circuit Board Layout.
1-324
Using the HCPL-2602/12
Line Receiver
Optocouplers
The primary objectives to fulfill
when connecting an optocoupler
to a transmission line are to
provide a minimum, but not
excessive, LED current and to
properly terminate the line. The
internal regulator in the HCPL2602/12 simplifies this task.
Excess current from variable drive
conditions such as line length
variations, line driver differences,
and power supply fluctuations are
shunted by the regulator. In fact,
with the LED current regulated,
the line current can be increased
to improve the immunity of the
system to differential-mode-noise
and to enhance the data rate
capability. The designer must
keep in mind the 60 mA input
current maximum rating of the
HCPL-2602/12 in such cases, and
may need to use series limiting or
shunting to prevent overstress.
Design of the termination circuit
is also simplified; in most cases
the transmission line can simply
be connected directly to the input
terminals of the HCPL-2602/12
without the need for additional
series or shunt resistors. If
reversing line drive is used it may
be desirable to use two HCPL2602/12 or an external Schottky
diode to optimize data rate.
Polarity Non-Reversing
Drive
High data rates can be obtained
with the HCPL-2602/12 with
polarity non-reversing drive.
Figure (a) illustrates how a
74S140 line driver can be used
with the HCPL-2602/12 and
shielded, twisted pair or coax
cable without any additional
components. There are some
reflections due to the “active
termination,” but they do not
interfere with circuit performance
because the regulator clamps the
line voltage. At longer line
lengths, tPLH increases faster than
tPHL since the switching threshold
is not exactly halfway between
asymptotic line conditions. If
optimum data rate is desired, a
series resistor and peaking
capacitor can be used to equalize
tPLH and tPHL. In general, the
peaking capacitance should be as
large as possible; however, if it is
too large it may keep the regulator
from achieving turn-off during the
negative (or zero) excursions of
the input signal. A safe rule:
make C ≤ 16t
where:
C = peaking capacitance in
picofarads
t = data bit interval in
nanoseconds
Polarity Reversing Drive
A single HCPL-2602/12 can also
be used with polarity reversing
drive (Figure b). Current reversal
is obtained by way of the
substrate isolation diode
(substrate to collector). Some
reduction of data rate occurs,
however, because the substrate
diode stores charge, which must
be removed when the current
changes to the forward direction.
The effect of this is a longer tPHL.
This effect can be eliminated and
data rate improved considerably
by use of a Schottky diode on the
input of the HCPL-2602/12.
For optimum noise rejection as
well as balanced delays, a splitphase termination should be used
along with a flip-flop at the
output (Figure c). The result of
current reversal in split-phase
operation is seen in Figure (c)
with switches A and B both
OPEN. The coupler inputs are
then connected in ANTI-SERIES;
however, because of the higher
steady-state termination voltage,
in comparison to the single
HCPL-2602/12 termination, the
forward current in the substrate
diode is lower and consequently
there is less junction charge to
deal with when switching.
Closing switch B with A open is
done mainly to enhance common
mode rejection, but also reduces
propagation delay slightly
because line-to-line capacitance
offers a slight peaking effect.
With switches A and B both
CLOSED, the shield acts as a
current return path which
prevents either input substrate
diode from becoming reversed
biased. Thus the data rate is
optimized as shown in Figure (c).
Improved Noise Rejection
Use of additional logic at the
output of two HCPL-2602/12s,
operated in the split phase
termination, will greatly improve
system noise rejection in addition
to balancing propagation delays
as discussed earlier.
A NAND flip-flop offers infinite
common mode rejection (CMR)
for NEGATIVELY sloped common
mode transients but requires tPHL
> tPLH for proper operation. A
NOR flip-flop has infinite CMR for
POSITIVELY sloped transients
but requires tPHL < tPLH for proper
operation. An exclusive-OR flipflop has infinite CMR for common
mode transients of EITHER
polarity and operates with either
tPHL > tPLH or tPHL < tPLH.
With the line driver and
transmission line shown in Figure
(c), tPHL > tPLH, so NAND gates are
preferred in the R-S flip-flop. A
higher drive amplitude or
1-325
Figure a. Polarity Non-Reversing.
Figure b. Polarity Reversing, Single Ended.
<1
<1
Figure c. Polarity Reversing, Split Phase.
Figure d. Flip-Flop Configurations.
1-326
different circuit configuration
could make tPHL < tPLH, in which
case NOR gates would be preferred. If it is not known whether
tPHL > tPLH or tPHL < tPLH, or if the
drive conditions may vary over
the boundary for these conditions,
the exclusive-OR flip-flop of
Figure (d) should be used.
RS-422 and RS-423
Line drivers designed for RS-422
and RS-423 generally provide
adequate voltage and current for
operating the HCPL-2602/12.
Most drivers also have
characteristics allowing the
HCPL-2602/12 to be connected
directly to the driver terminals.
Worst case drive conditions,
however, would require current
shunting to prevent overstress of
the HCPL-2602/12.
Propagation Delay, PulseWidth Distortion and
Propagation Delay Skew
Propagation delay is a figure of
merit which describes how
quickly a logic signal propagates
through a system. The propagation delay from low to high (tPLH)
is the amount of time required for
an input signal to propagate to
the output, causing the output to
change from low to high.
Similarly, the propagation delay
from high to low (tPHL) is the
amount of time required for the
input signal to propagate to the
output, causing the output to
change from high to low (see
Figure 6).
Pulse-width distortion (PWD)
results when tPLH and tPHL differ in
value. PWD is defined as the
difference between tPLH and tPHL
and often determines the
maximum data rate capability of a
transmission system. PWD can be
expressed in percent by dividing
the PWD (in ns) by the minimum
pulse width (in ns) being
transmitted. Typically, PWD on
the order of 20-30% of the
minimum pulse width is tolerable;
the exact figure depends on the
particular application (RS232,
RS422, T-1, etc.).
Propagation delay skew, tPSK, is an
important parameter to consider
in parallel data applications where
synchronization of signals on
parallel data lines is a concern. If
the parallel data is being sent
through a group of optocouplers,
differences in propagation delays
will cause the data to arrive at the
outputs of the optocouplers at
different times. If this difference
in propagation delays is large
enough, it will determine the
maximum rate at which parallel
data can be sent through the
optocouplers.
Propagation delay skew is defined
as the difference between the
minimum and maximum
propagation delays, either tPLH or
tPHL, for any given group of
optocouplers which are operating
under the same conditions (i.e.,
the same drive current, supply
voltage, output load, and
operating temperature). As
illustrated in Figure 16, if the
inputs of a group of optocouplers
are switched either ON or OFF at
the same time, tPSK is the
difference between the shortest
propagation delay, either tPHL or
tPHL, and the longest propagation
delay, either tPLH or tPHL.
As mentioned earlier, tPSK can
determine the maximum parallel
data transmission rate. Figure 17
is the timing diagram of a typical
parallel data application with both
the clock and the data lines being
sent through optocouplers. The
figure shows data and clock
signals at the inputs and outputs
of the optocouplers. To obtain the
maximum data transmission rate,
both edges of the clock signal are
being used to clock the data; if
only one edge were used, the
clock signal would need to be
twice as fast.
Propagation delay skew
represents the uncertainty of
where an edge might be after
being sent through an
optocoupler. Figure 17 shows
that there will be uncertainty in
both the data and the clock lines.
It is important that these two
areas of uncertainty not overlap,
otherwise the clock signal might
arrive before all of the data
outputs have settled, or some of
the data outputs may start to
change before the clock signal
has arrived. From these
considerations, the absolute
minimum pulse width that can be
sent through optocouplers in a
parallel application is twice tPSK. A
cautious design should use a
slightly longer pulse width to
ensure that any additional
uncertainty in the rest of the
circuit does not cause a problem.
The tPSK specified optocouplers
offer the advantages of
guaranteed specifications for
propagation delays, pulse-width
distortion and propagation delay
skew over the recommended
temperature, input current, and
power supply ranges.
1-327
DATA
II
INPUTS
50%
CLOCK
1.5 V
VO
II
DATA
50%
OUTPUTS
VO
1.5 V
t PSK
Figure 16. Illustration of Propagation Delay Skew tPSK.
1-328
t PSK
CLOCK
t PSK
Figure 17. Parallel Data Transmission Example.