AN1778 Rev.0.00 Page 1 of 4
Sep 12, 2012
USER’S MANUAL
AN1778
Rev.0.00
Sep 12, 2012
ISL28133CSENSEV1Z
Evaluation Board User Guide
Introduction
The ISL28133CSENSEV1Z evaluation board is designed
specifically for low side current sensing up to 10A of current.
The evaluation board uses a 1mΩ current sense resistor that is
capable of handling 4W of power dissipation. The ISL28133
micropower Zero Drift Amplifier gains the current sensing
input signal and can be used to directly drive ADC inputs.
The ISL28133CSENSEV1Z evaluation board is optimized to
operate at +5V. An ISL21070 micropower 2.5V voltage
reference sets a zero current reading of 2.5V at the amplifier
output to interface with ADCs operating at 5V. The voltage
reference raises the common mode input by approximately
40mV above GND at zero current flow. This connection enables
bi-directional current sensing, allowing the sense voltage to be
positive or negative relative to the common mode voltage. This
is helpful for applications such as the charging/discharging
current from an Electric Vehicle battery or motors that switch
polarity.
With the input common mode at 40mV above ground and a
1mΩ sense resistor, this allows ±40A current sensing before
amplifier saturation. However, due to PCB copper resistance
causing error at high currents, the recommended current
sense is ±10A.
Board Layout
The evaluation board is laid out with heavy duty screw lug
terminals that allow connections of wires up to 6 AWG. The
1mΩ sense resistance is formed from four 4mΩ 2512 style
resistors to increase power dissipation capacity of the sense
circuitry. The total power dissipation critically allowed is 4W.
The PCB board is made using 2oz copper PCB with the current
path routed on the top and bottom layer, minimizing trace
resistance to maintain accurate current sense resistance. To
further reduce sense errors, the current sensing uses a Kelvin
connection with the sense voltage pick up points at the center
of the current density distribution.
Amplifier U3 gains up the voltage drop developed across the
sense resistor from the current flow. Voltage Reference U2 sets
the zero current reading output of the amplifier at 2.5V.
Quick Setup Guide
1. Connect single supply +5VDC to +5V and GND terminals.
2. Connect low side load to terminal lugs. Current flows from
the top of the board to the bottom.
3. At no load, VOUT is 2.5V.
4. With 1mΩ sense resistance and amplifier gain of 63.5V/V,
the sense current reading is: (VOUT - 2.5V)/0.0635 in Amps.
Measuring Very High Current
The reference design is capable of sensing currents greater
than ±40A; however, it is limited mechanically from the
temperature rise of the copper PCB layout and current sense
resistor and limited electrically by amplifier saturation. One
must consider the temperature rise of the PCB trace from the
power dissipated under high currents, which may cause the
copper trace to delaminate. The high current carrying PCB
trace is made with 2oz copper on the FR4 board on both the
top and bottom layers. The trace dimension is approximately
25mm wide and 40mm long. Substantial vias connect the
planes for lower thermal impedance. The current sense
resistance is capable of 4W dissipation max.
o
FIGURE 1. ISL28133CSENSEV1Z EVALUATION BOARD
CONNECT
CONNECT
TO LOAD
TO SYSTEM GND
POSITIVE
CURRENT
FLOW
AMPLIFIER GND
+5V
VOUT
ISENSE = (VOUT - 2.5)
0.0635 AMP
REF PART NUMBER COMMENTS
U1 DNP Not Populated On Board
U2 ISL21070 Micropower 2.5V Voltage Reference
U3 ISL28133 Micropower Zero Drift Amplifier
CURRENT SENSE SPECIFICATIONS
Supply Voltage Range 3.0V to 5.0V
Optimized for 5V Operation
Max Sense Current ±10A recommended
±40A
Before Amplifier Saturation
Abs Max Sense Current 60 Amps
Thermally Limited by Sense Resistor
Current Sense Resolution ±10mA
Current Sense Accuracy 2%
Voltage to Current
Conversion
ISENSE = (VOUT - 2.5V) / 0.0635 Amps
Amplifier Bandwidth 6kHz
AN1778 Rev.0.00 Page 2 of 4
Sep 12, 2012
ISL28133CSENSEV1Z
Bill of Materials
PART NUMBER REFERENCE DESIGNATOR DESCRIPTION MANUFACTURER MANUFACTURER PART
DNP U1 DO NOT POPULATE OR PURCHASE
ISL21070CIH325Z U2 Low Power 2.5V Voltage Reference, SOT23 INTERSIL ISL21070CIH325Z
ISL28133FHZ U3 Low Power Zero Drift Amplifier, SOT23 INTERSIL ISL28133FHZ
H1045-00101-50V5-T C8, C9 CAP, SMD, 0603, 100pF, 50V, 5%, C0G, ROHS GENERIC
H1045-00102-50V5-T C4 CAP, SMD, 0603, 1000pF, 50V, 5%, C0G, ROHS GENERIC
H1045-00103-50V10-T C1, C3, C5, C6, C11 CAP, SMD, 0603, 0.01µF, 50V, 10%, X7R, ROHS GENERIC
H1045-00104-50V10-T C2 CAP, SMD, 0603, 0.1µF, 50V, 10%, X7R, ROHS GENERIC
H1045-DNP C7 CAP, SMD, 0603, DNP-PLACE HOLDER, ROHS
H1065-00475-50V10-T C10 CAP, SMD, 1206, 4.7µF, 50V, 10%, X5R, ROHS GENERIC
BAV99LT1G-T S1 DIODE-SWITCHING, SMD, SOT23, 70V, 0.2A,
ROHS
ON SEMICONDUCTOR BAV99LT1G
H2511-00R00-1/10W-T R7 RES, SMD, 0603, 0Ω, 1/10W, TF, ROHS GENERIC
H2511-01623-1/10W1-T R6, R9 RES, SMD, 0603, 162k, 1/10W, 1%, TF, ROHS GENERIC
H2511-02551-1/10W1-T R5, R10 RES, SMD, 0603, 2.55k, 1/10W, 1%, TF, ROHS GENERIC
H2511-DNP R8 RES, SMD, 0603, DNP-PLACE HOLDER, ROHS
H2515-0R004-1W1-T R1-R4 RES, SMD, 2512, 0.004Ω, 1W, 1%, TF, ROHS GENERIC
FIGURE 2. CURRENT SENSE AMPLIFIER SCHEMATIC
162k
100pF
2.55k
2.55kOPEN
4m1nF
10nF
10nF
0
DNP
162k
ISL28133
100pF
+5V
+2.5V
0.01µF
VOUT
R9
C9
R10
R5
C4
C3
C5 C8
R6
R8
ISL21090
1
2
3
4
8
7
6
5
+5V
10nF
0.1µF
4m4m4m
2.5V
VREF
SOIC-8
5 Ld
SOT23
ISL21070
2.5V
VREF
SOT-23
1
2
3
4.7µF 10nF
+5V
GND
TERMINAL
LUGS
R7
C7
C6
U1
U2
DNP
C2
C1
R1 R2 R3 R4
S1
C10 C11
TERMINAL
TERMINAL
U3
4
3
2
5
1
AN1778 Rev.0.00 Page 3 of 4
Sep 12, 2012
ISL28133CSENSEV1Z
FIGURE 3. CURRENT SENSE AMPLIFIER ASSEMBLY DRAWING
FIGURE 4. PCB TOP LAYER FIGURE 5. PCB BOTTOM LAYER
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