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| 型号： | MAX9938WEUK+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 12/14页 |
| 文件大小： | 0K |
| 描述： | IC AMP CURRENT SENSE SOT23-5 |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 放大器类型： | 电流检测 |
| 电路数： | 1 |
| -3db带宽： | 15kHz |
| 电压 - 输入偏移： | 100µV |
| 电流 - 电源： | 1.1µA |
| 电压 - 电源，单路/双路(±)： | 1.6 V ~ 28 V |
| 工作温度： | -45°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | SC-74A，SOT-753 |
| 供应商设备封装： | SOT-23-5 |
| 包装： | 带卷 (TR) |
MAX9938
1A, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
_______________________________________________________________________________________
7
Applications Information
Choosing the Sense Resistor
Choose RSENSE based on the following criteria:
Voltage Loss
A high RSENSE value causes the power-source voltage
to drop due to IR loss. For minimal voltage loss, use the
lowest RSENSE value.
OUT Swing vs. VRS+ and VSENSE
The MAX9938 is unique since the supply voltage is the
input common-mode voltage (the average voltage at
RS+ and RS-). There is no separate VCC supply voltage
pin. Therefore, the OUT voltage swing is limited by the
minimum voltage at RS+.
VOUT(max) = VRS+ (min) - VSENSE (max) - VOH
and
VSENSE full scale should be less than VOUT/gain at the
minimum RS+ voltage. For best performance with a
3.6V supply voltage, select RSENSE to provide approxi-
mately 120mV (gain of 25V/V), 60mV (gain of 50V/V),
30mV (gain of 100V/V), or 15mV (gain of 200V/V) of
sense voltage for the full-scale current in each applica-
tion. These can be increased by use of a higher mini-
mum input voltage.
Accuracy
In the linear region (VOUT < VOUT(max)), there are two
components to accuracy: input offset voltage (VOS) and
gain error (GE). For the MAX9938, VOS = 500μV (max)
and gain error is 0.5% (max). Use the linear equation:
VOUT = (gain ± GE) x VSENSE ± (gain x VOS)
to calculate total error. A high RSENSE value allows lower
currents to be measured more accurately because off-
sets are less significant when the sense voltage is larger.
Efficiency and Power Dissipation
At high current levels, the I2R losses in RSENSE can be
significant. Take this into consideration when choosing
the resistor value and its power dissipation (wattage)
rating. Also, the sense resistor’s value might drift if it is
allowed to heat up excessively. The precision VOS of
the MAX9938 allows the use of small sense resistors to
reduce power dissipation and reduce hot spots.
Kelvin Connections
Because of the high currents that flow through RSENSE,
take care to eliminate parasitic trace resistance from
causing errors in the sense voltage. Either use a four-
terminal current-sense resistor or use Kelvin (force and
sense) PCB layout techniques.
Optional Output Filter Capacitor
When designing a system that uses a sample-and-hold
stage in the ADC, the sampling capacitor momentarily
loads OUT and causes a drop in the output voltage. If
sampling time is very short (less than a microsecond),
consider using a ceramic capacitor across OUT and
GND to hold VOUT constant during sampling. This also
decreases the small-signal bandwidth of the current-
sense amplifier and reduces noise at OUT.
Input Filters
Some applications of current-sense amplifiers need to
measure currents accurately even in the presence of both
differential and common-mode ripple, as well as a wide
variety of input transient conditions. For example, high-fre-
quency ripple at the output of a switching buck or boost
regulator results in a common-mode voltage at the inputs
of the MAX9938. Alternatively, fast load-current transients,
when measuring at the input of a switching buck or boost
regulator, can cause high-frequency differential sense
voltages to occur at the inputs of the MAX9938, although
the signal of interest is the average DC value. Such high-
frequency differential sense voltages may result in a volt-
age offset at the MAX9938 output.
R
V
GI
SENSE
OUT
LOAD
=
×
(max)
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| MAX9939AUB+ | 功能描述:电流灵敏放大器 SPI-Programmable Gain Amplifier RoHS:否 制造商:Texas Instruments 通道数量: 共模抑制比（最小值）:110 dB 输入补偿电压:80 uV 电源电压-最大:5.5 V 电源电压-最小:2.7 V 电源电流:350 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-16 封装:Reel |
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