ISL28133ISENSEV1Z Evaluation Board User’s
Guide
The ISL28133ISENSEV1Z evaluation board contains a
complete precision current sense amplifier using the
ISL28133 chopper amplifier in a high side, low side of
floating supply current sense application.
The advantages of the ISL28133 in this application
include very low offset voltage (2µV typical) and offset
drift (0.07µV/°C), rail-to-rail input and output and low
power consumption (18µA typical). These features
provide a very high degree of precision for use in 5V,
low power applications.
Reference Documents
• ISL28133 Data Sheet (FN6560)
Evaluation Board Key Features
The ISL28133ISENSEV1Z operates from a single
1.65VDC to +5.5VDC supply. The current sense function
is configured as a single stage, balanced input,
trans-impedance amplifier. A 0.1Ω 0.1% current sense
resistor is used convert the incoming current to a voltage
which is applied to a precision differential amplifier with a
gain of 100. The overall current to voltage transfer ratio
is 10V/A, and a bidirectional current range of ±0.25A is
achieved when operating from a +5V supply, using a
2.5V reference voltage (V
achieves a total full scale offset error of 0.038% (when a
precision external reference is used) and approximately
0.15% using the internal 0.1% resistors.
The total current draw from the amplifier power is less
than 35µA and the total leakage current from the current
sense input is less than 3µA
Power Supply and Protection Features
External power connections are made through the +V,
and ground jacks. The single supply input is overvoltage
protected using a series 100Ω resistor and a 5.6V zener
diode (D1). Reverse polarity protection uses the 100Ω
resistor and two protection diode pairs (D3, D4). These
also provide input common mode voltage protection to
the op amp.
Input Protection Clamp Options
Included on the evaluation board are optional input
protection circuits that illustrate the best methods to
limit input common mode and differential transient
voltage spikes in exposed or electrically hazardous
applications. The ISL28133 can handle input common
mode and differential transients to a diode drop beyond
the rails, or to a range of -0.5V to +5.5V when
operating from a single 5V supply.
Clamp diodes D3A, B, D4A, B and input resistors R6, R7,
R8, R9 form a current limiting, 6V common mode and
differential voltage clamp. This clamp provides sufficient
April 14, 2011
AN1480.1
REF
1
). At +25°C, the ISL28133
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Application Note 1480
protection for the ISL28133 for common mode fault
voltages far beyond the power supply rails. These diodes
also provide the same 6V protection against large
differential transients.
High speed current sensing may involve filtering
repetitive current transients with high peak to average
values. In these cases, limiting these transient even
further will improve amplifier response and overload
settling time. The optional Schottky diode transient
clamp D2 reduces transients let through by the common
mode clamp from 6V down to ~ ±0.3V, which improves
overload recovery time. Capacitors C7 and C9 provide
common mode noise filtering and capacitor C8 can be
used to filter the current sense signal.
Current Sense Gain Equations
The current sense amplifier in Figure 1 forms a
trans-impedance amplifier whose gain is in units of V/A
and is determined by the ratios of resistor pairs. R11:R8
and R14: R9. Resistor R11 is set equal to R14 and R8 is
set equal to R9. This matching cancels the input offset
voltage errors caused by the op amp input bias currents,
leaving behind only the offset voltage errors caused by
the ISL28133 input offset current (I
The I
Equation 1:
where:
R11 = R14 and R6 + R8 = R7 + R9
On the evaluation board, the R12, R9 resistor ratio is
100:1 (499kΩ: 4.9kΩ), and R
impedance gain given by Equation 2:
Input Range and Offset Error Analysis
The ISL28133 output swings from rail-to-rail, and the
evaluation board has a bi-directional output range of
V
is set to V
selectable, internal V
reference (V
scale output range is 0 ±0.25A.
The very low offset voltage (±8µV +25°C max) and
offset current (300pA +25°C max) of the ISL28133
enable the use of very high values resistors for low
current consumption while maintaining excellent
precision in battery operated circuits. The total offset
voltage contribution of the ISL28133 is the sum of the
input offset voltage (V
produced by the input offset current (IOS) through the
V
---------------------- -
V
REF
I
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SENSE
SENSE
OUT
SENSE
±2.5V when operated from a +5V supply and V
=
=
I
S
SENSE
/2. The evaluation board contains a jumper-
10
to V
REF
V
--- -
A
OUT
pin). With V
×
R
SENSE
DC transfer function is given by
S
OS
/2 reference or an external
) and the offset voltage
×
R14
---------- -
R9
REF
SENSE
+
set to +2.5, the full
V
REF
OS
is 0.1Ω for a trans-
).
(EQ. 1)
(EQ. 2)
REF