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參數(shù)資料
| 型號(hào)： | MAX472EPA |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 電源管理 |
| 英文描述： | Precision, High-Side Current-Sense Amplifiers |
| 中文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDIP8 |
| 封裝： | PLASTIC, DIP-8 |
| 文件頁數(shù)： | 10/12頁 |
| 文件大?。?/td> | 120K |
| 代理商： | MAX472EPA |
M
In Figure 6, assume the load current to be measured is
10A and that you have determined a 0.3 inch wide, 2
ounce copper to be appropriate. The resistivity of 0.1
inch wide, 2 ounce copper is 30m
/ft (see Note 4). For
10A you may want R
SENSE
= 5m
for a 50mV drop at
full scale. This resistor will require about 2 inches of 0.1
inch wide copper trace.
RG1 and RG2
Once R
SENSE
is chosen, RG1 and RG2 can be chosen
to define the current-gain ratio (R
SENSE
/RG). Choose
RG = RG1 = RG2 based on the following criteria:
a)
1
Input Resistance.
The minimum RG value is lim-
ited by the 1
input resistance, and also by the out-
put current limitation (see below). As RG is reduced,
the input resistance becomes a larger portion of the
total gain-setting resistance. With RG = 50
, the
input resistance produces a 2% difference between
the expected and actual current-gain ratio. This is a
gain error that does not affect linearity and can be
removed by adjusting RG or R
OUT
.
b)
Efficiency.
As RG is reduced, I
OUT
gets larger for a
given load current. Power dissipated in R
OUT
is not
going to the load, and therefore reduces overall effi-
ciency. This is significant only when the sense cur-
rent is small.
c)
Maximum Output Current Limitation.
I
OUT
is limit-
ed to 1.5mA, requiring RG
≥
V
SENSE
/ 1.5mA. For
V
SENSE
= 60mV, RG must be
≥
40
.
d)
Headroom.
The MAX472 requires a minimum of
1.5V between the lower of the voltage at RG1 or
RG2 (V
RG_
) and V
OUT
. As RG becomes larger, the
voltage drop across RG also becomes larger for a
given I
OUT
. This voltage drop further limits the maxi-
mum full-scale V
OUT
. Assuming the drop across
R
SENSE
is small and V
CC
is connected to either side
of R
SENSE
, V
OUT
(max) = V
CC
- (1.5V + I
OUT
(max) x
RG).
e)
Output Offset Error at Low Load Currents.
Large
RG values reduce I
OUT
for a given load current. As
I
OUT
gets smaller, the 2.5μA max output offset-error
current becomes a larger part of the overall output
current. Keeping the gain high by choosing a low
value for RG minimizes this offset error.
f)
Input Bias Current and Input Bias Current
Mismatching.
The size of RG also affects the errors
introduced by the input bias and input bias mis-
matching currents. After selecting the ratio, check to
make sure RG is small enough that I
B
and I
OS
do
not add any appreciable errors. The full-scale error
is given by:
% Error = (RG1 - RG2) x I
B
+ I
OS
x RG x 100
I
FS
x R
SENSE
where RG1 and RG2 are the gain resistors, I
B
is the
bias current, I
OS
is the bias-current mismatch, I
FS
is the
full-scale current, and R
SENSE
is the sense resistor.
Assuming a 5A load current, 10m
R
SENSE
, and 100
RG, the current-gain ratio is 100μA/A, yielding a full-
scale I
OUT
of 500μA. Using the maximum values for I
B
(20μA) and I
OS
(2μA), and 1% resistors for RG1 and
RG2 (RG1 - RG2 = 2
), the worst-case error at full
scale calculates to:
2
x 20μA + 100
x 2μA= 0.48%
5m
x 5A
The error may be reduced by: a) better matching of
RG1 and RG2, b) increasing R
SENSE
, or c) decreasing
RG.
Current-Sense Adjustment
(Resistor Range, Output Adjust)
Choose R
OUT
after selecting R
SENSE
, RG1, and RG2.
Choose R
OUT
to obtain the full-scale voltage you
Prec ision, High-S ide
Current-S ense Amplifiers
10
______________________________________________________________________________________
Note 4:
Printed Circuit Design, by Gerald L. Ginsberg; McGraw-Hill, Inc.; page 185.
3V
TO
36V
R
SENSE
1
2
3
4
8
7
6
5
MAX472
0.1" COPPER
0.3" COPPER
0.3" COPPER
RG2
RG1
1.5k
1k
POWER
SOURCE
OR
BATTERY
TOLOAD/CHARGER
RG1
N.C.
SHDN
SIGN
OUT
V
CC
GND
RG2
Figure 6. MAX472 Connections Showing Use of PC Board
Trace
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| MAX472EPA+ | 功能描述:特殊用途放大器 RoHS:否 制造商:Texas Instruments 通道數(shù)量:Single 共模抑制比（最小值）: 輸入補(bǔ)償電壓: 工作電源電壓:3 V to 5.5 V 電源電流:5 mA 最大功率耗散: 最大工作溫度:+ 70 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-20 封裝:Reel |
| MAX472ESA | 功能描述:特殊用途放大器 RoHS:否 制造商:Texas Instruments 通道數(shù)量:Single 共模抑制比（最小值）: 輸入補(bǔ)償電壓: 工作電源電壓:3 V to 5.5 V 電源電流:5 mA 最大功率耗散: 最大工作溫度:+ 70 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-20 封裝:Reel |
| MAX472ESA/GH9 | 制造商:Maxim Integrated Products 功能描述:- Rail/Tube |
| MAX472ESA/PR | 制造商:Maxim Integrated Products 功能描述:- Rail/Tube |
| MAX472ESA+ | 功能描述:特殊用途放大器 RoHS:否 制造商:Texas Instruments 通道數(shù)量:Single 共模抑制比（最小值）: 輸入補(bǔ)償電壓: 工作電源電壓:3 V to 5.5 V 電源電流:5 mA 最大功率耗散: 最大工作溫度:+ 70 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-20 封裝:Reel |
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