MAX472CPA+ Maxim Integrated, MAX472CPA+ Datasheet - Page 7

• Manufacturer Part Number: MAX472CPA+
• Description: Special Purpose Amplifiers
• Manufacturer: Maxim Integrated
• Series: MAX471, MAX472r

Specifications of MAX472CPA+

• Rohs: yes
• Number Of Channels: Single
• Input Offset Voltage: 0.12 mV
• Operating Supply Voltage: 5 V, 9 V, 12 V, 15 V
• Supply Current: 0.02 mA
• Maximum Power Dissipation: 727 mW
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Supply Voltage - Max: 36 V
• Supply Voltage - Min: 3 V

The MAX471 and MAX472 current-sense amplifier’s
unique topology allows a simple design to accurately
monitor current flow. The MAX471/MAX472 contain two
amplifiers operating as shown in Figures 1 and 2. The
battery/load current flows from RS+ to RS- (or vice
versa) through R
RG1 and Q1 or RG2 and Q2, depending on the sense-
resistor current direction. Internal circuitry, not shown in
Figures 1 and 2, prevents Q1 and Q2 from turning on at
the same time. The MAX472 is identical to the
MAX471, except that R
RG1 and RG2 are external (Figure 2).
To analyze the circuit of Figure 1, assume that current
flows from RS+ to RS- and that OUT is connected to
GND through a resistor. In this case, amplifier A1 is
active and output current I
Q1. Since no current flows through RG2 (Q2 is off), the
negative input of A1 is equal to V
R
input to essentially the same level as the negative input.
Therefore, the drop across RG1 equals I
R
(ignoring the extremely low base currents), I
= I
Precision, High-Side
Current-Sense Amplifiers
6
_______________Detailed Description
______________________________________________________________Pin Description
SENSE
SENSE
MAX471
LOAD
_______________________________________________________________________________________
2, 3
6, 7
—
—
—
—
1
4
5
8
). The open-loop gain of A1 forces its positive
. Then, since I
x R
PIN
SENSE
MAX472
—
—
1
2
3
4
5
6
7
8
SENSE
, or:
SENSE
OUT
NAME
SHDN
. Current flows through either
SIGN
GND
N.C.
RG1
RG2
OUT
RS+
V
RS-
CC
OUT
flows through Q1 and RG
and gain-setting resistors
flows from the emitter of
Shutdown. Connect to ground for normal operation. When high, supply current is
less than 5µA.
Battery (or power) side of the internal current-sense resistor. The “+” indicates direction of
flow for SIGN output only. Connect pins 2 and 3 together at the package.
No Connect—no internal connection
Gain Resistor. Connect to battery side of current-sense resistor through the gain resistor.
Ground or Battery Negative Terminal
An open-collector logic output. For the MAX471, a low level indicates current is flowing from
RS- to RS+. For the MAX472, a low level indicates a negative V
high impedance when SHDN is high. Leave open if SIGN is not needed.
Load side of the internal current-sense resistor. The “-” indicates direction of flow for SIGN
output only. Connect pins 6 and 7 together at the package.
Gain Resistor. Connect to load side of current-sense resistor through the gain resistor.
Power input for MAX472. Connect to sense resistor (R
Current output that is proportional to the magnitude of the sensed current flowing through
R
sensed current in the MAX471.
SENSE
SOURCE
. A 2kΩ resistor from this pin to ground will result in a voltage equal to 1V/Amp of
OUT
- (I
LOAD
LOAD
x RG1
x
x
The output voltage equation for the MAX471/MAX472 is
given below. In the MAX471, the current-gain ratio has
been preset to 500µA/A so that an output resistor
(R
at ±3A. Other full-scale voltages can be set with differ-
ent R
greater than V
for the MAX472.
where V
I
the current-sense resistor, R
resistor, and RG = the gain-setting resistor (RG = RG1
= RG2).
The above equation can be modified to determine the
R
For the MAX471, this reduces to:
OUT is a high-impedance current-source output that
can be connected to other MAX471/MAX472 OUT pins
LOAD
OUT
OUT
OUT
required for a particular full-scale range:
) of 2kΩ yields 1V/A for a full-scale value of +3V
= the full-scale current being sensed, R
FUNCTION
OUT
I
V
R
R
OUT
values, but the output voltage can be no
OUT
OUT
OUT
= the desired full-scale output voltage,
RS+
= (I
= (R
= (V
= V
- 1.5V for the MAX471 or V
LOAD
OUT
SENSE
SENSE
OUT
/ (I
x R
x RG) / (I
) junction with RG1.
LOAD
x R
SENSE
SENSE
OUT
OUT
x 500µA/A)
(see Figure 2). SIGN is
LOAD
) / RG1
= the voltage-setting
x I
Current Output
LOAD
x R
) / RG
SENSE
RG_
SENSE
)
- 1.5V
=