Data Sheet
ACPL-C87B, ACPL-C87A, ACPL-C870
Precision Optically Isolated Voltage Sensor
Description
The Broadcom® ACPL-C87B/C87A/C870 voltage sensors
are optical isolation amplifiers designed specifically for
voltage sensing. Its 2V input range and high 1-GΩ input
impedance, makes it well suited for isolated voltage sensing
requirements in electronic power converters applications,
including motor drives and renewable energy systems. In a
typical voltage sensing implementation, a resistive voltage
divider is used to scale the DC-link voltage to suit the input
range of the voltage sensor. A differential output voltage that
is proportional to the input voltage is created on the other
side of the optical isolation barrier.
For general applications, the ACPL-C87A (±1% gain
tolerance) and the ACPL-C870 (±3% gain tolerance) are
recommended. For high precision requirements, the
ACPL-C87B (±0.5% gain tolerance) can be used. The
ACPL-C87B/C87A/C870 family operates from a single 5V
supply and provides excellent linearity. An active-high
shutdown pin is available which reduces the IDD1 current to
only 15A, making them suitable for battery-powered and
other power-sensitive applications.
The high common-mode transient immunity (15 kV/ms) of
the ACPL-C87B/C87A/C870 provides the precision and
stability needed to accurately monitor DC-link voltage in
high noise environments. Combined with superior optical
coupling technology, the ACPL-C87B/C87A/C870
implements sigma-delta (Σ-Δ) modulation, chopper
stabilized amplifiers, and differential outputs to provide
unequaled isolation-mode noise rejection, low offset, high
gain accuracy and stability. This performance is delivered in
a compact, auto-insertable Stretched SO-8 (SSO-8)
package that meets worldwide regulatory safety standards.
Broadcom
Features
Advanced sigma-delta (Σ-Δ) modulation technology
Unity gain 1 V/V, ±0.5% high gain accuracy
(ACPL-C87B)
1-GΩ input impedence
0 to 2V nominal input range
–35 ppm/°C low gain frift
21 µV /°C offset voltage drift
0.1% non-linearity max
Active-high shutdown pin
100-kHz wide bandwidth
3V to 5.5V wide supply range for output side
–40°C to +105°C operating temperature range
15 kV/µs common-mode transient immunity
Compact, auto-insertable stretched SO-8 package
Safety and regulatory approvals:
– IEC/EN/DIN EN 60747-5-5: 1414 Vpeak working
insulation voltage
– UL 1577: 5000 Vrms/1 min double protection rating
– CSA: Component Acceptance Notice #5
Applications
Isolated voltage sensing in AC and servo motor drives
Isolated DC-bus voltage sensing in solar inverters, wind
turbine inverters
Isolated sensor interfaces
Signal isolation in data acquisition systems
General purpose voltage isolation
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.
AV02-3563EN
December 18, 2017
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Functional Diagram
Table 1: Pin Description
Figure 1: Functional Diagram
Pin No.
Symbol
Description
1
VDD1
Supply voltage for input side (4.5V
to 5.5V), relative to GND1
2
VIN
Voltage input
3
SHDN
Shutdown pin (Active High)
4
GND1
Input side ground
5
GND2
Output side ground
6
VOUT–
Negative output
7
VOUT+
Positive output
8
VDD2
Supply voltage for output side (3V
to 5.5V), referenced to GND2
VDD1 1
8 VDD2
VIN 2
7 VOUT+
6 VOUT–
SHDN 3
GND1 4
NOTE:
SHIELD
5 GND2
A 0.1-µF bypass capacitor must be connected
between pins 1 and 4 and between pins 5 and 8.
Ordering Information
ACPL-C87B/C87A/C870 is UL recognized with 5000 Vrms/1 minute rating per UL 1577.
Table 2: Ordering Information
Option
Part Number
ACPL-C87B
ACPL-C87A
ACPL-C870
(RoHS
Compliant)
Package
Surface Mount
-000E
Stetched SO-8
X
-500E
X
Tape and Reel
X
IEC/EN/DIN EN
60747-5-5
Quantity
X
80 per tube
X
1000 per reel
To order, choose a part number from the part number column and combine with the desired option from the option column
to form an order entry.
Example:
ACPL-C87A-500E to order product of Surface Mount package in Tape and Reel packaging with IEC/EN/DIN EN
60747-5-5 Safety Approval and RoHS compliance.
Contact your Broadcom sales representative or authorized distributor for information.
Broadcom
AV02-3563EN
2
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Package Outline Drawing
Stretched SO-8 Package (SSO-8)
Figure 2: SSO-8 Package
RECOMMENDED LAND PATTERN
5.850 ± 0.254
(0.230 ± 0.010)
PART NUMBER
8
7
6
5
C87B
YWW
EEE
RoHS-COMPLIANCE
INDICATOR
1
2
DATE CODE
12.650
(0.498)
6.807 ± 0.127
(0.268 ± 0.005)
1.905
(0.075)
3
4
0.64
(0.025)
LOT ID
7°
0.450
(0.018)
1.590 ± 0.127
(0.063 ± 0.005)
45°
3.180 ± 0.127
(0.125 ± 0.005)
0.200 ± 0.100
(0.008 ± 0.004)
0.381 ± 0.127
(0.015 ± 0.005)
1.270
(0.050) BSG
0.750 ± 0.250
(0.0295 ± 0.010)
11.50 ± 0.250
(0.453 ± 0.010)
0.254 ± 0.100
(0.010 ± 0.004)
Dimensions in millimeters and (inches).
Note:
Lead coplanarity = 0.1 mm (0.004 inches).
Floating lead protrusion = 0.25mm (10mils) max.
Recommended Pb-Free IR Profile
Recommended reflow condition as per JEDEC Standard, J-STD-020 (latest revision). Non-Halide Flux should be used.
Regulatory Information
The ACPL-C87B/C87A/C870 is approved by the following organizations.
IEC/EN/DIN
EN 60747-5-5
Approval with Maximum Working Insulation Voltage VIORM = 1414 Vpeak.
UL
Approval under UL 1577, component recognition program up to VISO = 5000 Vrms/1 min. File 55361.
CSA
Approval under CSA Component Acceptance Notice #5, File CA 88324
Broadcom
AV02-3563EN
3
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Insulation and Safety Related Specifications
Table 3: Insulation and Safety Related Specifications
Parameter
Symbol
Value
Units
Minimum External Air Gap
(External Clearance)
L(101)
8.0
mm
Measured from input terminals to output terminals,
shortest distance through air
Minimum External Tracking
(External Creepage)
L(102)
8.0
mm
Measured from input terminals to output terminals,
shortest distance path along body
0.5
mm
Through insulation distance, conductor to conductor,
usually the direct distance between the photoemitter and
photodetector inside the optocoupler cavity
> 175
V
Minimum Internal Plastic Gap
(Internal Clearance)
Tracking Resistance (Comparative
Tracking Index)
Isolation Group
CTI
IIIa
Conditions
DIN IEC 112/VDE 0303 Part 1
Material Group (DIN VDE 0110, 1/89, Table 1)
IEC/EN/DIN EN 60747-5-5 Insulation Characteristics
Table 4: IEC/EN/DIN EN 60747-5-5 Insulation Characteristicsa
Description
Symbol
Value
Units
Installation classification per DIN VDE 0110/1.89, Table 1
for rated mains voltage ≤ 150 Vrms
I-IV
for rated mains voltage ≤ 300 Vrms
I-IV
for rated mains voltage ≤ 450 Vrms
I-IV
for rated mains voltage ≤ 600 Vrms
I-IV
for rated mains voltage ≤ 1000 Vrms
I-III
Climatic Classification
55/105/21
Pollution Degree (DIN VDE 0110/1.89)
Maximum Working Insulation Voltage
2
VIORM
1414
Vpeak
Input to Output Test Voltage, Method b
VIORM × 1.875 = VPR, 100% Production Test with tm = 1 second, Partial Discharge < 5 pC
VPR
2652
Vpeak
Input to Output Test Voltage, Method a
VIORM × 1.6 = VPR, Type and Sample Test, tm = 10 seconds, Partial Discharge < 5 pC
VPR
2262
Vpeak
VIOTM
8000
Vpeak
TS
175
°C
Input Current
IS,INPUT
230
mA
Output Power
PS,OUTPUT
600
mW
Highest Allowable Overvoltage (Transient Overvoltage, tini = 60 seconds)
Safety-limiting values (Maximum values allowed in the event of a failure)
Case Temperature
Insulation Resistance at TS, VIO = 500V
RS
≥
109
Ω
a. Insulation characteristics are guaranteed only within the safety maximum ratings, which must be ensured by protective circuits within the
application.
Broadcom
AV02-3563EN
4
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Absolute Maximum Rating
Table 5: Absolute Maximum Rating
Parameter
Symbol
Min.
Max.
Units
Storage Temperature
TS
–55
+125
°C
Ambient Operating Temperature
TA
–40
+105
°C
VDD1, VDD2
–0.5
6.0
V
Steady-State Input Voltagea, b
VIN
–2
VDD1 + 0.5
V
Two-Second Transient Input Voltagec
VIN
–6
VDD1 + 0.5
V
Logic Input
VSD
–0.5
VDD1 + 0.5
V
VOUT+, VOUT–
–0.5
VDD2 + 0.5
V
Supply Voltage
Output Voltages
Lead Solder Temperature
260° C for 10 seconds, 1.6 mm below seating plane
a. DC voltage of up to –2V on the inputs does not cause latch-up or damage to the device.
b. Absolute maximum DC current on the inputs = 100 mA, no latch-up or device damage occurs.
c. Transient voltage of 2 seconds up to –6V on the inputs does not cause latch-up or damage to the device.
Recommended Operating Conditions
Table 6: Recommended Operating Conditions
Parameter
Symbol
Min.
Max.
Units
TA
–40
+105
°C
VDD1 Supply Voltage
VDD1
4.5
5.5
V
VDD2 Supply Voltage
VDD2
3.0
5.5
V
Input Voltage Rangea
VIN
0
2.0
V
Shutdown Enable Voltage
VSD
VDD1 – 0.5
VDD1
V
Ambient Operating Temperature
a. 2V is the nominal input range. Full scale input range (FSR) is 2.46V.
Broadcom
AV02-3563EN
5
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Electrical Specifications
Unless otherwise noted, TA = –40°C to +105°C, VDD1 = 4.5V to 5.5V, VDD2 = 3.3V to 5.5V, VIN = 0V to 2V, and VSD = 0V.
Table 7: Electrical Specifications
Parameter
Symbol
Min.
Typ.a
Max.
Unit
Test Conditions/Notes
VOS
–9.9
–0.3
9.9
mV
TA = 25°C
|dVOS/dTA|
—
21
—
G0
0.995
1
1.005
V/V
TA = 25°C; VDD2 = 5V;
6, 7
b
0.994
0.999
1.004
V/V
TA = 25°C; VDD2 = 3.3V;
6, 7
b
Figure
Note
DC Characteristics
Input Offset Voltage
Magnitude of Input Offset Change
vs. Temperature
Gain (ACPL-C87B, ± 0.5%)
µV/°C TA = –40°C to +105°C;
Direct short across inputs.
3, 4
5
Gain (ACPL-C87A, ± 1%)
G1
0.99
1
1.01
V/V
TA = 25°C
6, 7
b
Gain (ACPL-C870, ± 3%)
G3
0.97
1
1.03
V/V
TA = 25°C
6, 7
b
dG/dTA
—
–35
—
NL
—
0.05
0.1
%
|dNL/dTA|
—
0.0002
—
%/°C
Recommended Input Range
VINR
—
2
—
V
Referenced to GND1
Full-Scale Differential Voltage Input
Range
FSR
—
2.46
—
V
Referenced to GND1
Shutdown Logic Low Input Voltage
VIL
—
0.8
—
TA = 25°C
Shutdown Logic High Input Voltage
VIH
VDD – 0.5
5
—
TA = 25°C
Input Bias Current
IIN
–0.1
–0.0015
—
µA
Magnitude of IIN Change vs.
Temperature
dIIN/dTA
—
1
—
nA/°C
Equivalent Input Impedance
RIN
—
1000
—
MΩ
Output Common-Mode Voltage
VOCM
—
1.23
—
V
VOUT+ or VOUT–
Output Voltage Range
VOUTR
—
Vocm ±
1.23
—
V
VSD = 0V
Output Short-Circuit Current
|IOSC|
—
30
—
mA
Output Resistance
ROUT
—
36
—
Ω
Vout Noise
Nout
—
0.013
—
Small-Signal Bandwidth (–3 dB)
f–3 dB
70
100
—
kHz
50% to 10%
tPD10
—
2.2
3.0
µs
Step input
18
50% to 50%
tPD50
—
3.7
5.5
µs
Step input
18
50% to 90%
tPD90
—
5.3
6.5
µs
Step input
18
Magnitude of Gain Change vs.
Temperature
Nonlinearity
Magnitude of NL Change vs.
Temperature
ppm/°C TA = –40°C to +105°C
VIN = 0 to 2V, TA = 25°C
TA = –40°C to +105°C
8
9, 10
11
Inputs and Outputs
VIN = 0 V
13
c
12
d
VOUT+ or VOUT–, shorted
to GND2 or VDD2
VOUT+ or VOUT–
AC Characteristics
mVrms Vin = 0V; output low-pass
filtered to 180 KHz.
Guaranteed by design
Input to Output Propagation Delay
Broadcom
AV02-3563EN
6
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Table 7: Electrical Specifications (Continued)
Symbol
Min.
Typ.a
Max.
Unit
Test Conditions/Notes
Output Rise/Fall Time (10% to 90%)
tR/F
—
2.7
4.0
µs
Step input (tPD90 – tPD10)
Shutdown Delay
tSD
—
25
40
µs
Vin = 2V
Enable Delay
tON
—
150
200
µs
Common Mode Transient Immunity
CMTI
10
15
—
Power Supply Rejection
PSR
—
–78
—
dB
1 Vpp 1-kHz sine wave
ripple on VDD1, differential
output
IDD1
—
10.5
15
mA
VSD = 0V
—
15
—
µA
VSD = 5V
—
6.5
12
mA
5V supply
—
6.1
11
mA
3.3V supply
Parameter
Figure
Note
17
kV/µs VCM = 1 kV, TA = 25°C
Power Supplies
Input Side Supply Current
IDD2
a. All Typical values are under Typical Operating Conditions at TA = 25°C, VDD1 = 5V, VDD2 = 5V.
b. Gain is defined as the slope of the best-fi t line of diff erential output voltage (VOUT+ – VOUT-) versus input voltage over the nominal range,
with offset error adjusted.
c. When VSD = 5V or when shutdown is enabled, Vout+ is close to 0V and Vout- is at close to 2.46V. This is similar to when VDD1 is not supplied.
d. Noise is measured at the output of the differential to single-ended post amplifier.
Package Characteristics
Table 8: Package Characteristics
Parameter
Symbol
Min
Typ
Max
Units
Test Conditions
Note
Input-Output Momentary Withstand
Voltage
VISO
5000
—
—
Vrms
RH < 50%, t = 1 min.,
TA = 25°C
Resistance (Input-Output)
RI-O
—
> 1012
—
Ω
VI-O = 500 VDC
c
Capacitance (Input-Output)
CI-O
—
0.5
—
pF
f = 1 MHz
c
a, b
a. In accordance with UL 1577, each optocoupler is proof-tested by applying an insulation test voltage ≥ 6000 Vrms for 1 second (leakage
detection current limit, II-O 5A). This test is performed before the 100% production test for partial discharge (method b) shown in IEC/EN/DIN
EN 60747-5-5 Insulation Characteristic Table.
b. 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 IEC/EN/DIN EN 60747-5-5 insulation characteristics table and your equipment
level safety specification.
c. This is a two-terminal measurement: pins 1 to 4 are shorted together and pins 5 to 8 are shorted together.
Broadcom
AV02-3563EN
7
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Typical Performance Plots
All ±3 (sigma symbol) plots are based on characterization test result at the point of product release. For guaranteed
specification, refer to the respective Electrical Specifications section.
Figure 4: Input Offset vs. Supply VDD2
5
4
3
2
1
0
-1
-2
-3
-4
-5
2
1.5
1
Offset (mV)
Offset (mV)
Figure 3: Input Offset vs. Supply VDD1
-0.5
-1.5
-2
5
Vdd1(V)
5.5
3.5
4
4.5
5
5.5
Figure 6: Gain vs. Supply VDD1
1.003
M+3
Mean
1.002
M- 3
1.001
Gain (V/V)
10
8
6
4
2
0
-2
-4
-6
-8
- 10
3
Vdd2 (V)
Figure 5: Input Offset vs. Temperature
Offset (mV)
0
-1
4.5
1.000
0.999
0.998
0.997
-55
-35
-15
5
25
45
Temp (qC)
65
85
105
4.5
125
Figure 7: Gain vs. Supply VDD2
1.003
1.00300
1.002
1.00200
1.001
1.00100
1.000
5.5
1.00000
0.999
0.99900
0.998
0.99800
0.99700
0.997
3
3.5
4
4.5
Vdd2 (V)
Broadcom
5
Vdd1 (V)
Figure 8: Gain vs. Temperature
Gain (V/V)
Gain (V/V)
0.5
5
5.5
-55
-35
-15
5
25 45
Temp (qC)
65
85
105 125
AV02-3563EN
8
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Figure 10: Non-Linearity vs. Supply VDD2
0.1
0.1
0.08
0.08
0.06
0.06
NL (%)
NL (%)
Figure 9: Non-Linearity vs. Supply VDD1
0.04
0.02
0.04
0.02
0
0
4.5
5
Vdd1 (V)
4.5
5
5.5
17
Vin = 0 V
Vin = 1 V
Vin = 2 V
15
AC Noise (mVrms)
13
11
9
7
5
3
1
-1
-55
-35
-15
5
25
45
Temp (qC)
65
85
105
0
125
Figure 13: VIN vs. VOUT+, VOUT-
20
40
60
80
100
Freq Filter (khz)
120
140
160
Figure 14: Frequency Response
3
1
VOUT+
VOUT–
2.5
0
-1
2
Gain (dB)
VOUT+, VOUT–
4
Figure 12: AC Noise vs. Filter Freq vs. Vin
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
1.5
1
-2
-3
-4
0.5
-5
0
0
Broadcom
3.5
Vdd2 (V)
Figure 11: Non-Linearity vs. Temperature
NL (%)
3
5.5
0.5
1
1.5
VIN
2
2.5
3
-6
1000
10000
Bandwidth (Hz)
100000
AV02-3563EN
9
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Figure 16: Propagation Delay vs Temperature
6
200
180
160
140
120
100
80
60
40
20
0
1000
5
Prog Delay (PS)
Phase (deg)
Figure 15: Phase Response
4
3
2
TPLH 50-10
TPLH 50-50
TPLH 50-90
1
0
10000
Bandwidth (Hz)
100000
-55
-35
-15
5
25
45
Temp (qC)
65
85
105
125
Figure 17: Shutdown And Wakeup Input To Output Timing Diagram. VOut Diff = VOut+ - VOut-
5V
VSD
0V
2V
Vin
0V
+2 V
VOut Diff
0V
tSD
tON
-2.46 V
Figure 18: Input to Output Propagation Delay Timing Diagram. VOut Diff = VOut+ – VOut-
2V
VIN
0V
2V
VOut Diff
0V
TPLH50-10
TPLH50-50
TPLH50-90
Broadcom
AV02-3563EN
10
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Definitions
Application Information
Gain
Application Circuit
Gain is defined as the slope of the best-fit line of differential
output voltage (VOUT+ – VOUT-) over the nominal input
range, with offset error adjusted out.
The typical application circuit is shown in Figure 19. The
ACPL-C87X voltage sensor is often used in photo-voltaic
(PV) panel voltage measurement and tracking in PV
inverters, and DC bus voltage monitoring in motor drivers.
The high voltage across rails needs to be scaled down to fit
the input range of the iso-amp by choosing R1 and R2
values according to appropriate ratio.
Nonlinearity
Nonlinearity is defined as half of the peak-to-peak output
deviation from the best-fit gain line, expressed as a
percentage of the full-scale differential output voltage.
Common Mode Transient Immunity,
CMTI, also known as Common Mode
Rejection
CMTI is tested by applying an exponentially rising/falling
voltage step on pin 4 (GND1) with respect to pin 5 (GND2).
The rise time of the test waveform is set to approximately
50 ns. The amplitude of the step is adjusted until the
differential output (VOUT+ – VOUT-) exhibits more than a 200
mV deviation from the average output voltage for more than
1 µs. The ACPL-C87x will continue to function if more than
10 kV/µs common mode slopes are applied, as long as the
breakdown voltage limitations are observed.
Power Supply Rejection, PSR
PSRR is the ratio of differential amplitude of the ripple
outputs over power supply ripple voltage, referred to the
input, expressed in dB.
Broadcom
The ACPL-C87X senses the single-ended input signal and
produces differential outputs across the galvanic isolation
barrier. The differential outputs (VOUT+, VOUT-) can be
connected to an op-amp to convert to a single-ended signal
or directly to two ADCs. The op-amp used in the external
post-amplifier circuit should be of sufficiently high precision
so that it does not contribute a significant amount of offset
or offset drift relative to the contribution from the isolation
amplifier. Generally, op-amps with bipolar input stages
exhibit better offset performance than op-amps with JFET or
MOSFET input stages.
In addition, the op-amp should also have enough bandwidth
and slew rate so that it does not adversely affect the
response speed of the overall circuit. The post-amplifier
circuit includes a pair of capacitors (C4 and C5) that form a
single-pole low-pass filter; these capacitors allow the
bandwidth of the post-amp to be adjusted independently of
the gain and are useful for reducing the output noise from
the isolation amplifier.
The gain-setting resistors in the post-amp should have a
tolerance of 1% or better to ensure adequate CMRR and
adequate gain tolerance for the overall circuit. Resistor
networks can be used that have much better ratio
tolerances than can be achieved using discrete resistors. A
resistor network also reduces the total number of
components for the circuit as well as the required board
space.
AV02-3563EN
11
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Figure 19: Typical Application Circuit
C5
100 pF
L1
1
U1
VDD1
VDD2
8
2
VIN
VOUT+
7
3
SHDN
VOUT-
6
4
GND1
GND2
5
VDD1
R1
R2
10K
C1
100 pF
C2
100 nF
GND1
VDD2
ACPL-C87X
R6
10K, 1%
V+
R3
10K,1%
C3
100 nF
Vout
R4
10K,1%
GND2
U2
OPA237
R5
10K, 1%
C4
100 pF
V-
L2
GND2
Measurement Accuracy and Power Dissipation of the Resistive Divider
The input stage of the typical application circuit in Figure 19
can be simplified as the diagram shown in Figure 20. R2
and RIN, input resistance of the ACPL-C87x, create a
current divider that results in an additional measurement
error component that will add on to the tot on top of the
device gain error. With the assumption that R1 and RIN
have a much higher value than R2, the resulting error can
be estimated to be R2/RIN.
Broadcom
R1
RIN
+
+–
With RIN of 1 GΩ for the ACPL-C87x, this additional
measurement error is negligible with R2 up to 1 MΩ, where
the error is approximately 0.1%. Though small, it can be
further reduced by reducing the R2 to 100 kΩ (error of
0.01% approximately), or 10 kΩ (error of 0.001%
approximately). However with lower R2, a drawback of
higher power dissipation in the resistive divider string needs
to be considered, especially in higher voltage sensing
applications. For example, with 600 V DC across L1 and L2
and R2 of 100 kΩ for 0.01% measurement error, the
resistive divider string consumes about 12 mW, assuming
VIN is set at 2V. If the R2 is reduced to 10 kΩ to reduce error
to 0.001%, the power consumption will increase to about
120 mW. In energy-efficiency critical applications, such as
PV inverters and battery-powered applications, this
trade-off between measurement accuracy and power
dissipation in the resistive string provides flexibility in design
priority.
Figure 20: Simplified Input Stage
R2
GND
ACPL-C87x
AV02-3563EN
12
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Isolated Temperature Sensing
Using a Thermistor
inside the module. In some cases, it is necessary to isolate
this thermistor to provide added isolation and insulation due
to the high power nature of the IGBTs. The ACPL-C87x
voltage sensor can be used to easily meet such a
requirement, while providing good accuracy and nonlinearity. Figure 21 shows an example of such an
implementation. The ACPL-C87x is used to isolate the
thermistor voltage which is later fed by the post amp stage
to an ADC onboard the microcontroller (MCU) to determine
the module temperature. The thermistor needs to be biased
in way that its voltage output will optimize the 2V input range
of the ACPL-C87x across the intended temperature
measurement range.
IGBTs are an integral part of a motor or servo drive system
and because of the high power that they usually handle, it is
essential that they have proper thermal management and
are sufficiently cooled. Long term overload conditions could
raise the IGBT module temperature permanently or failure
of the thermal management system could subject the
module to package overstress and lead to catastrophic
failures. One common way to monitor the temperature of the
module is through using a NTC type thermistor mounted
onto the IGBT module. Some IGBT module manufacturers
also have IGBTs that comes with the thermistor integrated
Figure 21: Thermistor Sensing in IGBT Module
HV+
U
V
W
Vdd
+–
+
GND
HVNTC Thermistor
IGBT Module
Broadcom
ACPL-C87x
Post
Amp
ADC
MCU
AV02-3563EN
13
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
Precision Optically Isolated Voltage Sensor
Power Supplies and Bypassing
As shown in Figure 22, 100-nF bypass capacitors (C2, C3)
should be located as close as possible to the pins of the
isolation amplifier. The bypass capacitors are required
because of the high-speed digital nature of the signals
inside the isolation amplifier. A 100-pF bypass capacitor
(Cin) is also recommended at the input pins due to the
switched-capacitor nature of the input circuit. The input
bypass capacitor Cin also forms part of the anti-aliasing
filter, which is recommended to prevent high-frequency
noise from aliasing down to lower frequencies and
interfering with the input signal. When R1 is far greater than
R2, the low-pass anti-aliasing filter corner frequency can be
calculated by 1/(2πR2Cin). The input filter also performs an
important reliability function—it reduces transient spikes
from ESD events flowing through the high voltage rails.
A power supply of 5V is required to power the ACPL-C87x
input side VDD1. In many motor drive DC bus voltage
sensing applications, this 5 V supply is most often obtained
from the same supply used to power the power transistor
gate drive circuit using an inexpensive 78L05 three-terminal
regulator. To help attenuate high frequency power supply
noise or ripple, a resistor or inductor can be used in series
with the input of the regulator to form a low-pass filter with
the regulator’s input bypass capacitor.
In some other applications, a dedicated supply might be
required to supply the VDD1. These applications include
photovoltaic (PV) inverter voltage tracking and
measurement, temperature sensor signal isolation. In these
cases it is possible to add an additional winding on an
existing transformer. Otherwise, some sort of simple
isolated supply can be used, such as a line powered
transformer or a high-frequency DC-DC converter module.
Figure 22: Recommended Power Supply and Bypassing
HV+
R1
Floating
Positive Supply
IN
78L05
C2
0.1PF
C1
0.1PF
Gate Drive
Circuit
OUT
5V
VDD2
VDD1
VOUT+
VIN
R2
Cin
0.1nF
ACPL-C87A
SHDN
VOUT-
GND1
GND2
C3
0.1PF
HV-
Broadcom
AV02-3563EN
14
ACPL-C87B, ACPL-C87A, ACPL-C870 Data Sheet
PC Board Layout
The design of the printed circuit board (PCB) should follow
good layout practices, such as keeping bypass capacitors
close to the supply pins, keeping output signals away from
input signals, the use of ground and power planes, and so
on. In addition, the layout of the PCB can also affect the
isolation transient immunity (CMTI) of the ACPL-C87x,
primarily due to stray capacitive coupling between the input
and the output circuits.
Broadcom
Precision Optically Isolated Voltage Sensor
To obtain optimal CMTI performance, the layout of the PC
board should minimize any stray coupling by maintaining
the maximum possible distance between the input and
output sides of the circuit and ensuring that any ground or
power plane on the PC board does not pass directly below
or extend much wider than the body of the ACPL-C87A. The
placement of the input capacitor which forms part of the antialiasing filter together with the resistor network should also
be placed as close as possible to the Vin pin.
AV02-3563EN
15
Broadcom, the pulse logo, Connecting everything, Avago Technologies, Avago, and the A logo are among the trademarks
of Broadcom and/or its affiliates in the United States, certain other countries and/or the EU.
Copyright © 2016–2017 Broadcom. All Rights Reserved.
The term “Broadcom” refers to Broadcom Limited and/or its subsidiaries. For more information, please visit
www.broadcom.com.
Broadcom reserves the right to make changes without further notice to any products or data herein to improve reliability,
function, or design. Information furnished by Broadcom is believed to be accurate and reliable. However, Broadcom does
not assume any liability arising out of the application or use of this information, nor the application or use of any product or
circuit described herein, neither does it convey any license under its patent rights nor the rights of others.
