MAX4378FASD View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX4378FASD Datasheet PDF : 9 Pages
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Single/Dual/Quad, High-Side Current-Sense
Amplifiers with Internal Gain
MAX4376
SOT23-5
1
2
3
4
5
—
PIN
MAX4376 MAX4377
SO-8
µMAX-8/
SO-8
4
1, 7
3
4
1
8
8
3, 5
6
2, 6
2, 5, 7
—
MAX4378
SO-14/
TSSOP-14
NAME
1, 7, 8, 14 OUT, OUT_
11
4
3, 5, 10, 12
2, 6, 9, 13
—
GND
VCC
RS+, RS_+
RS-, RS_-
N.C.
Pin Description
FUNCTION
Output Voltage. VOUT_ is proportional to the magnitude
of the sense voltage (VRS+ - VRS-). VOUT_ is
approximately zero when VRS - > VRS - + (no phase
reversal).
Ground
Supply Voltage
Power connection to the external sense resistor
Load-side connection to the external sense resistor
No Connection. Not internally connected.
Detailed Description
The MAX4376/MAX4377/MAX4378 high-side current-
sense amplifiers feature a 0 to +28V input common-mode
range that is independent of supply voltage. This feature
allows the monitoring of current out of a battery in deep
discharge and also enables high-side current sensing at
voltages greater than the supply voltage (VCC).
The MAX4376/MAX4377/MAX4378 operate as follows:
current from the source flows through RSENSE to the
load (Figure 1). Since the internal sense amplifier’s
inverting input has high impedance, negligible current
flows through RG2 (neglecting the input bias current).
Therefore, the sense amplifier’s inverting-input voltage
equals VSOURCE - (ILOAD)(RSENSE).
The amplifier’s open-loop gain forces its noninverting
input to the same voltage as the inverting input.
Therefore, the drop across RG1 equals (ILOAD)
(RSENSE). Since IRG1 flows through RG1, IRG1 =
(ILOAD)(RSENSE)/RG1. The internal current mirror multi-
plies IRG1 by a current gain factor, β, to give IRGD = β x
IRG1. Solving IRGD = β x (ILOAD)(RSENSE)/RG1.
Therefore:
VOUT = β x (RGD/RG1)(RSENSE x ILOAD) x amp gain
where amp gain is 2, 5, or 10.
The part’s gain equals (β x RGD / RG1) x amp gain.
Therefore:
VOUT = (GAIN)(RSENSE)(ILOAD)
where GAIN = 20 for MAX437_T.
GAIN = 50 for MAX437_F.
GAIN = 100 for MAX437_H.
Set the full-scale output range by selecting RSENSE and
the appropriate gain version of the MAX4376/
MAX4377/MAX4378.
Applications Information
Recommended Component Values
The MAX4376/MAX4377/MAX4378 sense a wide variety
of currents with different sense resistor values. Table 1
lists common resistor values for typical operation of the
MAX4376/MAX4377/MAX4378.
Choosing RSENSE
To measure lower currents more accurately, use a high
value for RSENSE. The high value develops a higher
sense voltage that reduces offset voltage errors of the
internal op amp.
In applications monitoring very high currents, RSENSE
must be able to dissipate the I2R losses. If the resistor’s
rated power dissipation is exceeded, its value may drift
or it may fail altogether, causing a differential voltage
across the terminals in excess of the absolute maxi-
mum ratings.
If ISENSE has a large high-frequency component, mini-
mize the inductance of RSENSE. Wire-wound resistors
have the highest inductance, metal-film resistors are
somewhat better, and low-inductance metal-film resis-
tors are best suited for these applications.
Bidirectional Current-Sense Amplifier
Systems such as laptop computers and other devices
that have internal charge circuitry require a precise
bidirectional current-sense amplifier to monitor accu-
rately the battery’s current regardless of polarity. Figure
2 shows the MAX4377 used as a bidirectional current
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