HP HCPL-2400

H
20 MBd High CMR Logic Gate
Optocouplers
Technical Data
HCPL-2400
HCPL-2430
Features
Applications
Description
• High Speed: 40 MBd Typical
Data Rate
• High Common Mode
Rejection:
HCPL-2400: 10 kV/µs at
VCM = 300 V (Typical)
• AC Performance Guaranteed
over Temperature
• High Speed AlGaAs Emitter
• Compatible with TTL, STTL,
LSTTL, and HCMOS Logic
Families
• Totem Pole and Tri State
Output (No Pull Up Resistor
Required)
• Safety Approval
UL Recognized – 2500 V rms
for 1 minute per UL1577
VDE 0884 Approved with
VIORM = 630 V peak (Option
060) for HCPL-2400
CSA Approved
• High Power Supply Noise
Immunity
• MIL-STD-1772 Version
Available (HCPL-5400/1 and
HCPL-5430/1)
• Isolation of High Speed
Logic Systems
• Computer-Peripheral
Interfaces
• Switching Power Supplies
• Isolated Bus Driver
(Networking Applications)
• Ground Loop Elimination
• High Speed Disk Drive I/O
• Digital Isolation for A/D,
D/A Conversion
• Pulse Transformer
Replacement
The HCPL-2400 and HCPL-2430
high speed optocouplers combine
an 820 nm AlGaAs light emitting
diode with a high speed
photodetector. This combination
results in very high data rate
capability and low input current.
The totem pole output (HCPL2430) or three state output
(HCPL-2400) eliminates the need
for a pull up resistor and allows
for direct drive of data buses.
Functional Diagram
HCPL-2400
HCPL-2430
VCC
1 NC
8
ANODE 1 1
8 VCC
ANODE 2
7 VE
CATHODE 1 2
7 VO1
CATHODE 3
6 VO
CATHODE 2 3
6 VO2
ANODE 2 4
5 GND
4 NC
GND
5
TRUTH TABLE
(POSITIVE LOGIC)
LED
ON
OFF
ON
OFF
ENABLE
L
L
H
H
OUTPUT
L
H
Z
Z
TRUTH TABLE
(POSITIVE LOGIC)
LED
OUTPUT
ON
L
OFF
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.
1-300
5965-3586E
The detector has optical receiver
input stage with built-in Schmitt
trigger to provide logic compatible
waveforms, eliminating the need
for additional waveshaping. The
hysteresis provides differential
mode noise immunity and minimizes the potential for output
signal chatter.
The electrical and switching
characteristics of the HCPL-2400
and HCPL-2430 are guaranteed
over the temperature range of
0°C to 70°C.
These optocouplers are
compatible with TTL, STTL,
LSTTL, and HCMOS logic
families. When Schottky type TTL
devices (STTL) are used, a data
rate performance of 20 MBd over
temperature is guaranteed when
using the application circuit of
Figure 13. Typical data rates are
40 MBd.
Selection Guide
8-Pin DIP (300 Mil)
Single
Channel
Package
HCPL-2400
Minimum CMR
Dual
Channel
Package
HCPL-2430
dV/dt
(V/µs)
1000
1000
500
500
500
VCM
(V)
300
50
50
50
50
Minimum Input
On Current
(mA)
4
4
6
6
6
Maximum
Propagation Delay
(ns)
60
60
60
60
60
Hermetic
Package
HCPL-540X*
HCPL-543X*
HCPL-643X*
*Technical data for the Hermetic HCPL-5400/01, HCPL-5430/31, and HCPL-6430/31 are on separate HP publications.
Ordering Information
Specify Part Number followed by Option Number (if desired).
Example:
HCPL-2400#XXX
060 = VDE 0884 VIORM = 630 V peak Option*
300 = Gull Wing Surface Mount Option
500 = Tape and Reel Packaging Option
*For HCPL-2400 only.
ICC
Schematic
ANODE
8
2 IF
+
ICC
8
IE
7
IO
6
VCC
VCC
IO
1 IF1
+
VF1
–
2
7
VO1
VE
VO
VF
CATHODE
–
5
3
TRUTH TABLE
(POSITIVE LOGIC)
LED
ON
OFF
ON
OFF
ENABLE
L
L
H
H
OUTPUT
L
H
Z
Z
GND
IO
3
–
VF2
+
4 IF2
6
5
SHIELD
VO2
GND
TRUTH TABLE
(POSITIVE LOGIC)
LED
OUTPUT
ON
L
OFF
H
1-301
Package Outline Drawings
8-Pin DIP Package (HCPL-2400, HCPL-2430)
7.62 ± 0.25
(0.300 ± 0.010)
9.65 ± 0.25
(0.380 ± 0.010)
TYPE NUMBER
8
7
6
5
6.35 ± 0.25
(0.250 ± 0.010)
OPTION CODE*
DATE CODE
HP XXXXZ
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)
DIMENSIONS IN MILLIMETERS AND (INCHES).
2.54 ± 0.25
(0.100 ± 0.010)
*MARKING CODE LETTER FOR OPTION NUMBERS
"V" = OPTION 060
OPTION NUMBERS 300 AND 500 NOT MARKED.
8-Pin DIP Package with Gull Wing Surface Mount Option 300
(HCPL-2400, HCPL-2430)
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).
1-302
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.
TEMPERATURE – °C
Solder Reflow Temperature Profile
(Gull Wing Surface Mount Option 300 Parts)
260
240
220
200
180
160
140
120
100
80
60
40
20
0
∆T = 145°C, 1°C/SEC
∆T = 115°C, 0.3°C/SEC
∆T = 100°C, 1.5°C/SEC
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-24XX has been
approved by the following
organizations:
VDE
Approved according to VDE
0884/06.92 (Option 060 only).
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
Minimum External
Air Gap (External
Clearance)
Minimum External
Tracking (External
Creepage)
Minimum Internal
Plastic Gap
(Internal Clearance)
Symbol
L(101)
Value
7.1
Units
mm
L(102)
7.4
mm
Measured from input terminals to output
terminals, shortest distance path along body.
0.08
mm
Tracking Resistance
(Comparative
Tracking Index)
Isolation Group
CTI
200
Volts
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
IIIa
Conditions
Measured from input terminals to output
terminals, shortest distance through air.
Material Group (DIN VDE 0110, 1/89, Table 1)
Option 300 - surface mount classification is Class A in accordance with CECC 00802.
1-303
VDE 0884 Insulation Related Characteristics
(HCPL-2400 OPTION 060 ONLY)
Description
Installation classification per DIN VDE 0110/1.89, Table 1
for rated mains voltage ≤ 300 V rms
for rated mains voltage ≤ 450 V rms
Climatic Classification
Pollution Degree (DIN VDE 0110/1.89)
Maximum Working Insulation Voltage
Input to Output Test Voltage, Method b*
VIORM x 1.875 = VPR, 100% Production Test with tm = 1 sec,
Partial Discharge < 5 pC
Input to Output Test Voltage, Method a*
VIORM x 1.5 = VPR, Type and sample test,
tm = 60 sec, Partial Discharge < 5 pC
Highest Allowable Overvoltage*
(Transient Overvoltage, tini = 10 sec)
Safety Limiting Values
(Maximum values allowed in the event of a failure,
also see Figure 12, Thermal Derating curve.)
Case Temperature
Input Current
Output Power
Insulation Resistance at TS, VIO = 500 V
Symbol
Characteristic
Units
VIORM
I-IV
I-III
55/85/21
2
630
V peak
VPR
1181
V peak
VPR
945
V peak
VIOTM
6000
V peak
TS
IS,INPUT
PS,OUTPUT
RS
175
230
600
≥ 109
°C
mA
mW
Ω
*Refer to the front of the optocoupler section of the current catalog, under Product Safety Regulations section (VDE 0884) for a
detailed description.
Note: Isolation characteristics are guaranteed only within the safety maximum ratings which must ben ensured by protective circuits
in application.
1-304
Absolute Maximum Ratings
(No derating required up to 70°C)
Parameter
Symbol
Minimum
Maximum
Units
Storage Temperature
TS
-55
125
°C
Operating Temperature
TA
-40
85
°C
IF(AVG)
10
mA
IFPK
20
mA
Reverse Input Voltage
VR
2
V
Three State Enable Voltage
(HCPL-2400 Only)
VE
-0.5
10
V
Supply Voltage
VCC
0
7
V
Average Output Collector Current
IO
-25
25
mA
Output Collector Voltage
VO
-0.5
10
V
Output Voltage
VO
-0.5
18
V
Output Collector Power Dissipation
(Each Channel)
PO
40
mW
Total Package Power Dissipation
(Each Channel)
PT
350
mW
Average Forward Input Current
Peak Forward Input Current
Lead Solder Temperature
(for Through Hole Devices)
260°C for 10 sec., 1.6 mm below seating plane
Reflow Temperature Profile
(Option #300)
See Package Outline Drawings section
Note
12
Recommended Operating Conditions
Parameter
Power Supply Voltage
Forward Input Current (ON)
Forward Input Voltage (OFF)
Fan Out
Enable Voltage (Low)
HCPL-2400 Only)
Enable Voltage (High)
HCPL-2400 Only)
Operating Temperature
Symbol
VCC
IF(ON)
VF(OFF)
N
VEL
Minimum
4.75
4
0
Maximum
5.25
8
0.8
5
0.8
Units
V
mA
V
TTL Loads
V
VEH
2
VCC
V
TA
0
70
°C
1-305
Electrical Specifications
0°C ≤ TA ≤ 70°C, 4.75 V ≤ VCC ≤ 5.25 V, 4 mA ≤ IF(ON) ≤ 8 mA, 0 V ≤ VF(OFF) ≤ 0.8 V. All typicals at TA = 25°C,
VCC = 5 V, IF(ON) = 6.0 mA, VF(OFF) = 0 V, except where noted. See Note 11.
Device
Parameter
Symbol HCPL- Min. Typ.* Max. Units
Logic Low Output Voltage
VOL
0.5
V
Test Conditions
Fig.
IOL = 8.0 mA (5 TTL Loads) 1
Logic High Output
Voltage
VOH
V
IOH = -4.0 mA
IOH = -0.4 mA
Output Leakage Current
Logic High Enable Current
IOHH
VEH
100
VO = 5.25 V, VF = 0.8 V
2400
µA
V
Logic Low Enable Voltage
Logic High Enable
Current
VEL
IEH
2400
2400
0.8
20
V
µA
VE = 2.4 V
Logic Low Enable Current
IEL
2400
-0.28
100
-0.4
mA
VE = 5.25 V
VE = 0.4 V
Logic Low Supply Current
ICCL
2400
19
26
mA
Logic High Supply
Current
ICCH
2430
2400
34
17
46
26
mA
2430
32
42
High Impedance State
Supply Current
High Impedance State
Output Current
ICCZ
2400
22
28
mA
VCC = 5.25 V, VE = 5.25 V
IOZL
2400
20
µA
VO = 0.4 V
20
100
µA
µA
VO = 2.4 V
VO = 5.25 V
2.4
2.7
2.0
IOZH
IOZH
Note
2
VCC = 5.25 V, VE = 0 V,
IO = Open
VCC = 5.25 V, IO = Open
VCC = 5.25 V, VE = 0 V,
IO = Open
VCC = 5.25 V, IO = Open
VE = 2 V
Logic Low Short Circuit
Output Current
IOSL
52
mA
VO = VCC = 5.25 V,
IF = 8 mA
2
Logic High Short Circuit
Output Current
IOSH
-45
mA
VCC = 5.25 V, IF = 0 mA,
VO = GND
2
Input Current Hysteresis
Input Forward Voltage
IHYS
VF
0.25
1.1
mA
VCC = 5 V
TA = 25°C
Input Reverse Breakdown
Voltage
BVR
1.0
3.0
Temperature
Coefficient of
Forward Voltage
∆VF
∆TA
-1.44
Input Capacitance
CIN
20
1.3
3
IF = 8 mA
1.55
5.0
4
V
TA = 25°C
IR = 10 µA
2.0
*All typical values at TA = 25°C and VCC = 5 V, unless otherwise noted.
1-306
1.5
mV/°C IF = 6 mA
pF
f = 1 MHz, VF = 0 V
4
Switching Specifications
0°C ≤ TA ≤ 70°C, 4.75 V ≤ VCC ≤ 5.25 V, 4 mA ≤ IF(ON) ≤ 8 mA, 0 V ≤ VF(OFF) ≤ 0.8 V. All typicals at TA = 25°C,
VCC = 5 V, IF(ON) = 6.0 mA, VF(OFF) = 0 V, except where noted. See Note 11.
Parameter
Symbol
Propagation Delay
Time to Logic Low
Output Level
tPHL
Propagation Delay
Time to Logic High
Output Level
tPLH
Pulse Width
Distortion
Device
HCPL- Min. Typ.*
15
Max.
Units
55
ns
IF(ON) = 7 mA
5, 6, 7
1, 4,
5, 6
ns
IF(ON) = 7 mA
5, 6, 7
1, 4,
5, 6
ns
IF(ON) = 7 mA
5, 8
6
ns
Per Notes & Text
15, 16
7
33
|tPHL-tPLH|
Figure Note
60
55
15
Test Conditions
30
60
2
15
5
25
35
Propagation Delay
Skew
tPSK
Output Rise Time
tr
20
ns
5
Output Fall Time
tf
10
ns
5
Output Enable Time
to Logic High
tPZH
2400
15
ns
9, 10
Output Enable Time
to Logic Low
tPZL
2400
30
ns
9, 10
Output Disable Time
from Logic High
tPHZ
2400
20
ns
9, 10
Output Disable Time
from Logic Low
tPLZ
2400
15
ns
9, 10
Logic High Common
Mode Transient
Immunity
|CMH|
1000 10,000
V/µs
VCM = 300 V, TA = 25°C,
IF = 0 mA
11
9
Logic Low Common
Mode Transient
Immunity
|CML|
1000 10,000
V/µs
VCM = 300 V, TA = 25°C,
IF = 4 mA
11
9
Power Supply Noise
Immunity
PSNI
Vp-p
VCC = 5.0 V,
48 Hz ≤ = FAC ≤ 50 MHz
0.5
10
*All typical values at TA = 25°C and VCC = 5 V, unless otherwise noted.
1-307
Package Characteristics
Parameter
Input-Output
Momentary
Withstand Voltage**
Sym.
VISO
Device
Min.
2500
Typ.*
Max.
Units
V rms
Test Conditions
RH ≤ 50%,
t = 1 min.,
TA = 25°C
Input-Output
Resistance
Input-Output
Capacitance
Input-Input
Insulation Leakage
Current
Resistance
(Input-Input)
Capacitance
(Input-Input)
RI-O
1012
Ω
VI-O = 500 Vdc
CI-O
0.6
pF
II-I
2430
0.005
µA
RI-I
2430
1011
Ω
f = 1 MHz
VI-O = 0 Vdc
RH ≤ 45%
t = 5 s,
VI-I = 500 Vdc
VI-I = 500 Vdc
CI-I
2430
0.25
pF
f = 1 MHz
Fig.
Note
3, 13
3
8
8
8
*All typical values are at TA = 25°C.
**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 Related Characteristics Table (if
applicable), your equipment level safety specification or HP Application Note 1074 entitled “Optocoupler Input-Output Endurance
Voltage,” publication number 5963-2203E.
Notes:
1. Each channel.
2. Duration of output short circuit time
not to exceed 10 ms.
3. Device considered a two terminal
device: pins 1, 2, 3, and 4 shorted
together, and pins 5, 6, 7, and 8
shorted together.
4. tPHL propagation delay is measured
from the 50% level on the rising edge
of the input current pulse to the 1.5 V
level on the falling edge of the output
pulse. The tPLH propagation delay is
measured from the 50% level on the
falling edge of the input current pulse
to the 1.5 V level on the rising edge of
the output pulse.
5. The typical data shown is indicative of
what can be expected using the
application circuit in Figure 13.
1-308
6. This specification simulates the worst
case operating conditions of the
HCPL-2400 over the recommended
operating temperature and VCC range
with the suggested application circuit
of Figure 13.
7. Propagation delay skew is discussed
later in this data sheet.
8. Measured between pins 1 and 2
shorted together, and pins 3 and 4
shorted together.
9. Common mode transient immunity in a
Logic High level is the maximum
tolerable (positive) dVCM /dt of the
common mode pulse, VCM, to assure
that the output will remain in a Logic
High state (i.e., VO > 2.0 V. Common
mode transient immunity in a Logic
Low level is the maximum tolerable
(negative) dVCM /dt of the common
mode pulse, VCM, to assure that the
output will remain in a Logic Low state
(i.e., VO < 0.8 V).
10. Power Supply Noise Immunity is the
peak to peak amplitude of the ac ripple
voltage on the VCC line that the device
will withstand and still remain in the
desired logic state. For desired logic
high state, VOH(MIN) > 2.0 V, and for
desired logic low state,
VOL(MAX) < 0.8 V.
11. Use of a 0.1 µF bypass capacitor
connected between pins 8 and 5
adjacent to the device is required.
12. Peak Forward Input Current pulse
width < 50 µs at 1 KHz maximum
repetition rate.
13. In accordance with UL 1577, each
optocoupler is proof tested by applying
an insulation test voltage ≥ 3000 V rms
for one second (leakage detection
current limit, II-O ≤ 5 µA). This test is
performed before the 100% Production test shown in the VDE 0884
Insulation Related Characteristics
Table, if applicable.
Figure 1. Typical Logic Low Output
Voltage vs. Logic Low Output Current.
Figure 2. Typical Logic High Output
Voltage vs. Logic High Output Current.
Figure 4. Typical Diode Input Forward
Current Characteristic.
Figure 5. Test Circuit for tPLH, tPHL, tr, and tf.
Figure 6. Typical Propagation Delay
vs. Ambient Temperature.
Figure 7. Typical Propagation Delay
vs. Input Forward Current.
Figure 3. Typical Output Voltage vs.
Input Forward Current.
Figure 8. Typical Pulse Width Distortion
vs. Ambient Temperature.
1-309
Figure 10. Typical Enable Propagation
Delay vs. Ambient Temperature.
Figure 9. Test Circuit for tPHZ, tPZH, tPLZ and tPZL.
VCC
HCPL-2400/11
+
VFF
–
B
A
8
0.1 µF *
2
7
3
6
4 NC
GND
5
OUTPUT VO
MONITORING NODE
†
CL = 15 pF
VCM
+
–
PULSE GENERATOR
OUTPUT POWER – PS, INPUT CURRENT – IS
1 NC
IF
VCC
800
PS (mW)
700
IS (mA)
600
500
400
300
200
100
0
0
25
50
75 100 125 150 175 200
TS – CASE TEMPERATURE – °C
Figure 12. Thermal Derating Curve,
Dependence of Safety Limiting Value
with Case Temperature per VDE 0884.
Figure 11. Test Diagram for Common Mode Transient Immunity
and Typical Waveforms.
1-310
Applications
HCPL-2400
HCPL-2400
V
Figure 13. Recommended 20 MBd HCPL-2400/30 Interface Circuit.
Figure 14. Alternative HCPL-2400/30
Interface Circuit.
DATA
IF
INPUTS
50%
CLOCK
1.5 V
VO
IF
DATA
50%
OUTPUTS
VO
1.5 V
t PSK
CLOCK
t PSK
Figure 15. Illustration of Propagation Delay Skew – tPSK.
Figure 17. Modulation Code Selections.
t PSK
Figure 16. Parallel Data Transmission Example.
Figure 18. Typical HCPL-2400/30 Output Schematic.
1-311
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 5).
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
1-312
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 15, 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 tPLH or tPHL, and the
longest propagation delay, either
tPLH or tPHL.
As mentioned earlier, tPSK can
determine the maximum parallel
data transmission rate. Figure 16
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 signals
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 16 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 tPHZ.
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 HCPL-2400/30 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.
Application Circuit
A recommended LED drive circuit
is shown in Figure 13. This circuit
utilizes several techniques to
minimize the total pulse-width
distortion at the output of the
optocoupler. By using two
inverting TTL gates connected in
series, the inherent pulse-width
distortion of each gate cancels the
distortion of the other gate. For
best results, the two seriesconnected gates should be from
the same package.
The circuit in Figure 13 also uses
techniques known as prebias and
peaking to enhance the
performance of the optocoupler
LED. Prebias is a small forward
voltage applied to the LED when
the LED is off. This small prebias
voltage partially charges the
junction capacitance of the LED,
allowing the LED to turn on more
quickly. The speed of the LED is
further increased by applying
momentary current peaks to the
LED during the turn-on and turnoff transitions of the drive
current. These peak currents help
to charge and discharge the
capacitances of the LED more
quickly, shortening the time
required for the LED to turn on
and off.
Switching performance of the
HCPL-2400/30 optocouplers is
not sensitive to the TTL logic
family used in the recommended
drive circuit. The typical and
worst-case switching parameters
given in the data sheet can be met
using common 74LS TTL inverting gates or buffers. Use of faster
TTL families will slightly reduce
the overall propagation delays
from the input of the drive circuit
to the output of the optocoupler,
but will not necessarily result in
lower pulse-width distortion or
propagation delay skew. This
reduction in overall propagation
delay is due to shorter delays in
the drive circuit, not to changes in
the propagation delays of the
optocoupler; optocoupler propagation delays are not affected by
the speed of the logic used in the
drive circuit.
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