MAX34406 Maxim, MAX34406 Datasheet - Page 8

• Manufacturer Part Number: MAX34406
• Description: The MAX34406 is a quad, high-side, unidirectional, current-sense amplifier that offers precision accuracy
• Manufacturer: Maxim

The MAX34406 quad-channel, unidirectional, high-side,
current-sense amplifier features a 2.0V to 28V input
common-mode range. This feature allows the monitoring
of current out of a voltage supply as low as 2.0V. The
device monitors current through a current-sense resistor
and amplifies the voltage across that resistor.
Current-sense amplifier output voltages (OUT1 to OUT4)
are compared to a fixed 1.0V reference; if V
exceeds 1.0V, the corresponding overcurrent warning
output (OC1 to OC4) is asserted. If the enable input
(ENA) is logic-high, SHTDN asserts when any of the four
overcurrent outputs go logic-high. Assertion of SHTDN on
overcurrent can be delayed and/or filtered by attaching
an external capacitor to CDLY. Once SHTDN is latched
high impedance, it remains so until ENA is toggled.
The unidirectional current-sense amplifiers used in each
channel of the device have a well established history. For
each channel, an op amp is used to force the current
through an internal gain resistor at IN+, which has a value
of R1, such that its voltage drop equals the voltage drop
across an external sense resistor, R
internal resistor at IN- with the same value as R1 to mini-
mize offset voltage. The current through R1 is sourced by
a high-voltage p-channel FET. Its source current is the
same as its drain current, which flows through a second
gain resistor, R
V
The gain accuracy is based on the matching of the two
gain resistors, R1 and R
for the MAX34406T, 50V/V for the MAX34406F, 100V/V
for the MAX34406H, and 200V/V for the MAX34406W.
The output is protected from input overdrive by use of a
6V clamp-protection circuit.
Table 1. Internal Gain Setting Resistors
(Typical Values)
OUTx
GAIN (V/V)
, whose magnitude is I
200
100
50
25
OUTx
����������������������������������������������������������������� Maxim Integrated Products 8
. This produces an output voltage,
with Overcurrent Threshold Comparators
OUTx
Detailed Description
R1 (I)
100
100
200
400
LOAD
(Table
x R
1). Total gain = 25V/V
SENSE
SENSE
R
. There is an
OUTx
x R
20
10
10
10
OUTx
(kI)
Quad Current-Sense Amplifier
OUTx
/R1.
Choose R
lowing sections.
A high R
to drop due to IR loss. For minimal voltage loss, use the
lowest R
The device is unique because the supply voltage for
the current-sense amplifier in each channel is the input
common-mode voltage for that channel (the average
voltage at INx+ and INx-). There are no separate supply
voltage pins for the current-sense amplifiers. Therefore,
the OUTx voltage swing for a given channel is limited by
the minimum voltage at IN+ for that channel.
and
V
minimum INx+ voltage. For best performance with a 3.6V
supply voltage, select R
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 application. These can be
increased by use of a higher minimum input voltage.
In the linear region (V
two components to accuracy: input offset voltage (V
and gain error (GE). For all variants of the device,
V
MAX34406T/F/H or 0.8% (max) for the MAX34406W. Use
the linear equation to calculate total error:
where GE is gain error, V
the sense resistor R
high R
more accurately because offsets are less significant
when the sense voltage is larger.
SENSE
OS
V
= P 600FV (max); gain error is 0.6% (max) for the
OUTx(MAX)
SENSE
full scale should be less than V
SENSE
SENSE
SENSE
Error (%) GE
value allows lower currents to be measured
R
value.
value causes the power-source voltage
SENSE
Applications Information
based on the criteria detailed in the fol-
= V
Choosing the Sense Resistor
OUTx Swing vs. V
SENSE
INx+(MIN)
=
OUTx
=
SENSE
G I
, and V
±
V
SENSE
×
OUTx



LOAD
V
< V
- V
SENSE
to provide approximately
V
MAX34406
OS
SENSE(MAX)
(MAX)
OUTx(MAX)
OS
is the voltage across
(MAX)
is offset voltage. A



INx+
×
OUTx
100
Voltage Loss
and V
), there are
/gain at the
- V
Accuracy
OH
SENSE
OS
)