Avago Technologies ACPL-C870-000E - Manual (Page 3)

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With the ACPL-C87x gain of 1 and P4 jumper position on P1-2, the overall transfer function is:
- Equation 2
- Equation 3
or
As long as the P4 jumper position remains on P1-2, then Equation 2 and 3 hold true. If the P4 jumper is changed to P2-3,
then the V
REF
in Equation 2 and 3 will be set to 0 V. In this case, the onboard offset calibration function discussed in the
subsequent section cannot be used.
Output voltage V
OUT
representing the line voltage on the high voltage side is connected to the controller through P7
pin 7.
Power Supplies
The ACPL-C87x evaluation board operates from a single 5 V or dual supply up to ±15 V. To operate the board from a
single 5 V supply:
1. Leave header jumpers P3 through P6 at their default positions as indicated in the schematic (Figure 3).
2. Connect the 5 V supply source to nodes V
DD2
and GND2 through P7 pin 1 and 2. In many cases, the 5 V supply is the
same power supply for the signal processing and control device.
To operate the board from dual supply such as ±10 V:
1. Connect +10 V, COM and -10 V to nodes V+, GND2 and V- through P7 pin 3, 4 and 5, respectively.
2. Change P5 and P6 jumpers pin 2-3 position, respectively.
In the dual supply method, the V
DD2 [1]
node receives 5 V supply through a voltage regulator LM78L05 (U6) from V+
node; therefore, a recommendation for V+ node is +7 V to +15 V.
Besides supplying to the ACPL-C87x output side, it is also connected to an isolated DC-DC converter (U3) to produce a
floating 5 V supply. This floating 5 V supply, denoted as V
DD1
, is used to operate the ACPL-C87x input side and the ACPL-
W50L optocoupler. The isolated DC-DC converter is included in the evaluation board for evaluation convenience. To
make this isolated voltage sensing solution cost-effective in mass production, the 5 V supply would usually be supplied
by a floating power supply, which in many applications could be the same supply that is used to drive the high-side
power transistor. A simple three-terminal voltage regulator will provide a stable voltage. Another method is to add an
additional winding to an existing transformer to produce a 5 V supply.
Note:
1. The ACPL-C87X data sheet specifies VDD2 of 3 V to 5.5 V.
Onboard Offset Calibration
A voltage reference device, the U5 LT6650 in Figure 3, is included in the circuit to provide a shifted “virtual ground” for
VOUT, thereby enables onboard offset calibration. To use this function, follow these simple steps:
1. Provide power supply to the board. Ensure the P4 jumper position is at Pin 1-2.
2. Set line voltage to the evaluation board to 0 V, or leave it unconnected.
3. Adjust the trimmer resistor R13 to set V
OUT
reading at 0.500 V.
With these steps, V
OUT
of 0.500 V corresponds to a 0 V of V
IN
, therefore offset voltage due to the voltage sensor ACPL-
C87x and the post-amp OPA237 is calibrated out. The controlled offset of 0.500 V then needs to be registered in the fol-
lowing stage signal processor and subtracted from measurement readings to obtain actual voltage sensor input.
Voltage Sensor Shutdown
The voltage sensor ACPL-C87x features a shutdown mode, which can be activated with a high level logic input on the
shutdown pin (pin 3). In this mode, the IDD1 supply current is reduced to only 15 µA, making it suitable for battery-pow-
ered devices and other power-sensitive applications. In the evaluation circuit, the optocoupler U2 ACPL-W50L sends
the shutdown logic from the low voltage controller side across the isolation barrier to the voltage sensor shutdown pin
SHDN. Controller shutdown signal through P7 pin 9 needs to be a Low logic as the ACPL-W50L produces inversed signal
from input to output. To manually turn the ACPL-C87x to shutdown mode, jumper P3 can be used: put jumper on pin
1-2 for normal operation; change to pin 2-3 to shut down.