参数资料
型号: LT6109HMS-1#TRPBF
厂商: Linear Technology
文件页数: 3/28页
文件大小: 0K
描述: IC AMP CURRENT SENSE 10MSOP
标准包装: 2,500
类型: 放大器,比较器,参考
应用: 电流感测,电源管理
安装类型: 表面贴装
封装/外壳: 10-TFSOP,10-MSOP(0.118",3.00mm 宽)
供应商设备封装: 10-MSOP
包装: 带卷 (TR)
LT6109-1/LT6109-2
11
610912fa
APPLICATIONS INFORMATION
The output current can be transformed back into a voltage
by adding a resistor from OUTA to V(typically ground).
The output voltage is then:
VOUT = V+ IOUTA ROUT
where ROUT = R1 + R2 + R3 as shown in Figure 3.
Table 1. Example Gain Configurations
GAIN
RIN
ROUT VSENSE FOR VOUT = 5V IOUTA AT VOUT = 5V
20
499Ω
10k
250mV
500A
50
200Ω
10k
100mV
500A
100
100Ω
10k
50mV
500A
Useful Equations
Input Voltage: VSENSE = ISENSE RSENSE
Voltage Gain:
VOUT
VSENSE
=
ROUT
RIN
Current Gain:
IOUTA
ISENSE
=
RSENSE
RIN
Note that VSENSE(MAX) can be exceeded without damag-
ing the amplifier, however, output accuracy will degrade
as VSENSE exceeds VSENSE(MAX), resulting in increased
output current, IOUTA.
Selection of External Current Sense Resistor
The external sense resistor, RSENSE,hasasignificanteffect
on the function of a current sensing system and must be
chosen with care.
First, the power dissipation in the resistor should be
considered. The measured load current will cause power
dissipation as well as a voltage drop in RSENSE. As a
result, the sense resistor should be as small as possible
while still providing the input dynamic range required by
the measurement. Note that the input dynamic range is
the difference between the maximum input signal and the
minimum accurately reproduced signal, and is limited
primarily by input DC offset of the internal sense ampli-
fier of the LT6109. To ensure the specified performance,
RSENSE should be small enough that VSENSE does not
exceed VSENSE(MAX) under peak load conditions. As an
example, an application may require the maximum sense
voltage be 100mV. If this application is expected to draw
2A at peak load, RSENSE should be set to 50mΩ.
Once the maximum RSENSE value is determined, the mini-
mum sense resistor value will be set by the resolution or
dynamic range required. The minimum signal that can be
accurately represented by this sense amplifier is limited by
theinputoffset.Asanexample,theLT6109hasamaximum
input offset of 125V. If the minimum current is 20mA, a
sense resistor of 6.25mΩ will set VSENSE to 125V. This is
the same value as the input offset. A larger sense resistor
will reduce the error due to offset by increasing the sense
voltage for a given load current. Choosing a 50mΩ RSENSE
will maximize the dynamic range and provide a system
that has 100mV across the sense resistor at peak load
(2A), while input offset causes an error equivalent to only
2.5mA of load current.
In the previous example, the peak dissipation in RSENSE
is 200mW. If a 5mΩ sense resistor is employed, then
the effective current error is 25mA, while the peak sense
voltage is reduced to 10mV at 2A, dissipating only 20mW.
The low offset and corresponding large dynamic range of
theLT6109makeitmoreflexiblethanothersolutionsinthis
respect.The125Vmaximumoffsetgives72dBofdynamic
range for a sense voltage that is limited to 500mV max.
Sense Resistor Connection
Kelvin connection of the SENSEHI and SENSELO inputs
to the sense resistor should be used in all but the lowest
power applications. Solder connections and PC board
interconnections that carry high currents can cause sig-
nificant error in measurement due to their relatively large
resistances.One10mm
×10mmsquaretraceof1ozcopper
is approximately 0.5mΩ. A 1mV error can be caused by as
little as 2A flowing through this small interconnect. This
will cause a 1% error for a full-scale VSENSE of 100mV.
A 10A load current in the same interconnect will cause
a 5% error for the same 100mV signal. By isolating the
sense traces from the high current paths, this error can
be reduced by orders of magnitude. A sense resistor with
integrated Kelvin sense terminals will give the best results.
Figure3illustratestherecommendedmethodforconnect-
ing the SENSEHI and SENSELO pins to the sense resistor.
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