an1777

Application Note 1777
Author: Tim Lok
Low Side Precision Current Sense Amplifier
Introduction
The ISL28134ISENSEV1Z 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 ISL28134
Precision Low Noise Zero Drift Amplifier gains the current
sensing input signal and can be used to directly drive ADC
inputs.
The ISL28134ISENSEV1Z evaluation board is optimized to
operate at +5V. An ISL21090 Precision Low Noise 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 also 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.
CONNECT
TO LOAD
ISENSE =
POSITIVE
CURRENT
FLOW
(VOUT - 2.5)
0.0635
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 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 flow from
top to bottom of board.
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.
REF
PART NUMBER
U1
ISL21090
U2
DNP
U3
ISL28134
Not populated on board
Ultra Low Noise 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
AMP
Abs Max Sense Current
VOUT
COMMENTS
Ultra Low Noise 2.5V Voltage Reference
60 Amps
Thermally Limited by Sense Resistor
Current Sense Resolution
±5mA
Current Sense Accuracy
2%
Voltage to Current
Conversion
ISENSE = (VOUT - 2.5V) / 0.0635 Amps
Amplifier Bandwidth
10kHz
Measuring Very High Current
+5V
AMPLIFIER GND
CONNECT
TO SYSTEM GND
FIGURE 1. ISL28134ISENSEV1Z EVALUATION BOARD
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
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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 FR4 board both top and
bottom layers. The trace dimension is approximately 25mm
width and 40mm length. Substantial vias are used to connect
the planes for lower thermal impedance. The current sense
resistance is capable of 4W dissipation max.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Copyright Intersil Americas Inc. 2012. All Rights Reserved.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
All other trademarks mentioned are the property of their respective owners.
Application Note 1777
Bill of Materials
PART NUMBER
REFERENCE DESIGNATOR
DESCRIPTION
MANUFACTURER
ISL21090BFB825Z
U1
Low Noise 2.5V Voltage Reference, SOIC-8
DNP
U2
DO NOT POPULATE
ISL28134FHZ
U3
H1045-00101-50V5-T
MANUFACTURER PART
INTERSIL
ISL21090BFB825Z-TK
Low Noise Zero Drift Amplifier, SOT-23
INTERSIL
ISL28134FHZ
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
C9
100pF
R9
C3
10nF
162kΩ
2.55kΩ
S1
+5V
4
R10
TERMINAL
LUGS
R1
4mΩ
R2
4mΩ
R3
4mΩ
5
C4
1nF
R4
4mΩ
U3
5 Ld
SOT23
2
R5
0Ω
1
ISL28134
VOUT
R7
3
+5V
U1
1
2
3
4
C8
100pF
+2.5V
7
162kΩ
6
R6
5
0.01µF
R8
DNP
C6
+5V
TERMINAL
3
C10
4.7µF
U2
DNP
ISL21070
2.5V
VREF
SOT-23
C11
10nF
GND
TERMINAL
2
0.1µF
C2
1
10nF
C1
8
ISL21090
2.5V
VREF
SOIC-8
C7
OPEN
2.55kΩ
10nF
C5
FIGURE 2. CURRENT SENSE AMPLIFIER SCHEMATIC
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Application Note 1777
FIGURE 3. CURRENT SENSE AMPLIFIER ASSEMBLY DRAWING
FIGURE 4. PCB TOP LAYER
FIGURE 5. PCB BOTTOM LAYER
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is
cautioned to verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
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