参数资料
型号: ADM4073TWRJZ-REEL7
厂商: ANALOG DEVICES INC
元件分类: 电源管理
英文描述: Low Cost, Voltage Output, High-Side, Current-Sense Amplifier
中文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO6
封装: LEAD FREE, MO-178AB, SOT-23, 6 PIN
文件页数: 10/12页
文件大小: 212K
代理商: ADM4073TWRJZ-REEL7
ADM4073
THEORY OF OPERATION
The current from the source flows through R
SENSE
, which
generates a voltage drop, V
SENSE
, across the RS+ and RS
terminals of the sense amplifier. The Input Stage Amplifier A1
regulates its inputs to be equal, thereby shunting a current
proportional to V
SENSE
/R
G1
to the output current mirror. This
current is then multiplied by a gain factor b in the output stage
current mirror and flows through R
GD
to generate V
OUT
.
Therefore, V
OUT
is related to V
SENSE
by the ratio of R
G1
to R
GD
and
the current gain b.
V
OUT
=
A
V
×
V
SENSE
Rev. 0 | Page 10 of 12
where:
A
V
=
R
GD
/
R
G1
×
b
where:
A
V
= 20 V/V (for ADM4073T).
A
V
= 50 V/V (for ADM4073H).
A
V
= 100 V/V (for ADM4073F).
2V TO 28V
3V TO 28V
0.1μF
V
OUT
R
SENSE
I
LOAD
I
RG1
V
OUT
RS+
GND
AV
RS–
V
CC
RG2
RGD = 12k
RG1
ADM4073
I
RGD
MIRROR
0
Figure 25. Functional Block Diagram
R
SENSE
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, for example, 10 V for 10 A.
Then select a gain model that gives the most efficient use of the
sense voltage range (150 mV max).
In the example above, using the ADM4073H (gain of 100) give
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:
R
SENSE
= 100 mV/10 A
R
SENSE
= 10 mΩ
V
OUT
= (
I
LOAD
×
R
SENSE
)
×
A
V
To measure lower currents accurately, as large a sense resistor
as possible should be used 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
2
R
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
altogether. 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, a sense resistor with low inductance
should be chosen.
INPUT
COPPER PCB TRACE
OUTPUT
3V TO 28V
0.1μF
R
SENSE
OUT
RS+
GND
RS–
V
CC
ADM4073
0
Figure 26. Using PCB Trace for Current Sensing
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:
(
/
100
%
=
OUT
LOAD
R
R
Error
)
(
)
1
_
+
SENSE
INT
R
where:
R
LOAD
is the external load applied to OUT.
R
OUT_INT
is the internal output resistance (12 kΩ).
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