ADM4073 Analog Devices, ADM4073 Datasheet - Page 10

• Manufacturer Part Number: ADM4073
• Description: Low Cost, Voltage Output, High-side Current Sense Amplifier
• Manufacturer: Analog Devices

Specifications of ADM4073

• Filter Option: No
• Common Mode Input (v)min: +2V
• Common Mode Input (v)max: +28V
• Bandwidth G=10 (khz Typ): 1800kHz
• Cmrr (db): 90dB
• Vcc-vee: 3V to 28V

ADM4073
THEORY OF OPERATION
The current from the source flows through R
erates a voltage drop, V
of the sense amplifier. The Input Stage Amplifier A1 regulates
its inputs to be equal, thereby shunting a current proportional
to V
multiplied by a gain factor of b in the output stage current mir-
ror and flows through R
related to V
of b.
where:
A
A
the device.
•
•
•
R
The ADM4073 has the ability to sense a wide variety of currents
by selecting a particular sense resistor. Select a suitable output
voltage for full-scale current, such as 10 V for 10 A. Then, select
a gain model that gives the most efficient use of the sense volt-
age range (150 mV max).
In the example above, using the ADM4073H (gain of 100) gives
an output voltage of 10 V when the sense voltage is 100 mV.
Use the following equation to determine what value of sense
resistor gives 100 mV with 10 A flowing through it:
V
v
SENSE
is equal to different voltages depending upon the model of
= R
SENSE
V
20 V/V for ADM4073T.
50 V/V for ADM4073F.
100 V/V for ADM4073H.
R
R
V
SENSE
SENSE
OUT
OUT
GD
3V TO 28V
2V TO 28V
/R
/R
= A
= (I
0.1µF
G1
= 100 mV/10 A
= 10 mΩ
SENSE
G1
to the output current mirror. This current is then
× b
V
LOAD
× V
by the ratio of R
Figure 25. Functional Block Diagram
V
× R
CC
SENSE
SENSE
CURRENT
SENSE
GD
MIRROR
R
RS+
GND
) × A
G1
to generate V
I
, across the RS+ and RS− terminals
RGD
ADM4073
R
SENSE
I
V
RG1
AV
G1
to R
I
R
LOAD
GD
RS–
R
= 12kΩ
GD
G2
OUT
and the current gain
. Therefore, V
SENSE
OUT
, which gen-
V
OUT
V
OUT
OUT
is
Rev. A | Page 10 of 12
To measure lower currents accurately, use as large a sense
resistor as possible to utilize the higher end of the sense voltage
range. This reduces the effects of the offset voltage errors in the
internal amplifier.
When currents are very large, it is important to take the I
power losses across the sense resistor into account. If the sense
resistor’s rated power dissipation is not sufficient, its value can
drift, giving an inaccurate output voltage or it could fail alto-
gether. This, in turn, causes the voltage across the RS+ and RS−
pins to exceed the absolute maximum ratings.
If the monitored supply rail has a large amplitude high
frequency component, choose a sense resistor with low
inductance.
OUTPUT (OUT)
The output stage of the ADM4073 is a current source driving a
pull-down resistance. To ensure optimum accuracy, care must
be taken not to load this output externally. To minimize output
errors, ensure OUT is connected to a high impedance input
stage. If this is not possible, output buffering is recommended.
The percent error introduced by output loading is determined
with the following formula:
where:
R
R
LOAD
OUT_INT
%
is the external load applied to OUT.
Error
is the internal output resistance (12 kΩ).
3V TO 28V
INPUT
Figure 26. Using PCB Trace for Current Sensing
=
0.1µF
100
(
1
−
COPPER PCB TRACE
R
V
CC
LOAD
RS+
ADM4073
R
GND
SENSE
/
(
R
OUT
RS–
OUT
_
INT
+
R
LOAD
OUTPUT
)
)
2
R