Silicon Laboratories si85xx User Manual
Si85xx-TB UG
Si85XX U
The Si85xx products are unidirectional ac current sensors available with full scale current sense input ranges of 5,
10, and 20 A. Si85xx products are ideal upgrades for older current-sensing technologies offering size, performance
and cost advantages over current transformers, Hall Effect devices, DCR circuits, and other approaches. The
Si85xx are extremely low-loss, adding less than 1.3 mΩ of series resistance and less than 2 nH series inductance
in the sensing path at 25 ºC. Current-sensing terminals are isolated from the other package pins to a maximum
voltage of 1,000 VDC.
NIDIRECTIONAL
AC C
URRENT SENSOR TARGET BOARD USER’S GUIDE
1. Kit Contents
The Si85xx Unidirectional AC Current Sensor Development Kit contains the following items:
10 Amp Si8512 based evaluation board
Si85xx Unidirectional AC Current Sensor Target Board User's Guide (this document)
2. Hardware Overview
The Si85xx Target Board (Si85xx-TB, see Figure 1) provides a means to evaluate the ac current sensor in an
existing application. It is meant to be soldered directly into the users existing power supply. The board comes with
the Si8512 installed and provides a 10 Amp full scale input sense range and a 2.0 V full scale output voltage. For
more details on the Si8512, refer to the Si85xx Data Sheet.
Figure 1. Si85xx-TB Overview
Rev. 0.1 6/07 Copyright © 2007 by Silicon Laboratories Si85xx-TB UG
Si85xx-TB UG
3. Si85xx-TB Hardwired to Single-Phase POL
Figure 2 illustrates the Si85xx-TB soldered directly into a single-phase POL. The single phase POL was designed
to operate at a 400 kHz switch rate and provide better than 90 percent efficiency. It also provides 10 amps of peak
current to the load and protects the supply by shutting down in the event of an over current condition.
Figure 2. Si85xx-EVB Hardwired to Single-phase POL
Figure 3 illustrates the Si8512 accurately monitoring the POL's switching current. As shown in the scope plot, a
1.6 V peak output voltage accurately monitors the 8 Amp peak, 50 percent duty cycle, 400 kHz current signal of the
POL. A 20 mΩ sense resistor in series with the Si85xx is also monitored via a differential probe to provide a baseline measurement of the POL.
20 mΩ
Si8512
Sense Resistor
Figure 3. Si85xx-TB OUT1 Oscilloscope Plot
To accommodate this test, the Si85xx-TB was powered with a 5 V (100 mA) supply connected from J1 to J2. R1
was soldered from J4 to the respective phase control line of the POL. R2 and R4 were jumped to GND on J4. R3
was tied to 5 V and the Mode pin was jumped to VDD via J7.
2 Confidential Rev. 0.1
Si85xx-TB UG
4. Si85xx Evaluation Board
The Si85xx-TB has a Si8512 installed. Refer to Figure 4 for the locations of the various I/O connectors and major
components.
J1 5 V Supply Input power connection 5 V, 100 mA
J2 GND, Input Supply power return connection, 0 V
J3 HDR-2X2, Mode Control input
J4 HDR-2X07, R1, R2, R3, R4 inputs, OUT1, OUT2 outputs, and seven GND return pins
J5 IIN Positive Current Sense Input
J6 IOUT Negative/return Current Sense Input
J7 HEADER, TRST timing select jumper, default tied to VDD
Figure 4. Si85xx-TB Layout
4.1. VIN (J1, J2)
The user-provided power supply should be connected to connectors J1 and J2 where J2 is the reference. The
power source must be 5 V with at least 100 mA maximum output current.
Table 1. J1, J2 Pin Descriptions
Jumper # Description
J1 5 V, 100 mA
J2 GND
4.2. Mode Pin (J3)
Connector J3 is the Mode Control header. The user should tie this pin to either VDD or GND depending on their
power supply.
Table 2. J3 Pin Descriptions
Jumper # Description
J3 VDD or GND
Confidential Rev. 0.1 3
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