MAX9934 Maxim, MAX9934 Datasheet - Page 11

• Manufacturer Part Number: MAX9934
• Description: The MAX9934 high-precision, low-voltage, high-side current-sense amplifier is ideal for both bidirectional (charge/discharge) and unidirectional current measurements in battery-powered portable and laptop devices
• Manufacturer: Maxim

voltage. Further, when V
an extremely high impedance on both its inputs and
output, up to the maximum operating voltages (see the
Absolute Maximum Ratings section).
The MAX9934 features a CS that can be used to dese-
lect its output current-source. This allows multiple cur-
rent-sense amplifier outputs to be multiplexed into a
single ADC channel with a single R
Select Functionality for Multiplexed Systems section for
more details.
The Functional Diagram shows the internal operation of
the MAX9934. At its core is the indirect current-feed-
back architecture. This architecture uses two matched
transconductance amplifiers to convert their input dif-
ferential voltages into an output current. A high-gain
feedback amplifier forces the voltage drop across
R
The internal resistor (R
gain of the device. Both input and output transconduc-
tance amplifiers feature excellent common-mode rejec-
tion characteristics, helping the MAX9934 to deliver
industry-leading precision specifications over the full
common-mode range.
Figure 2. Output Select and Deselect Time
High-Precision, Low-Voltage, Current-Sense Amplifier
GAIN
with Current Output and Chip Select for Multiplexing
V
0V
V
CS
OUT
to be the same as the input differential voltage.
1.8V
______________________________________________________________________________________
% FINAL VALUE
GAIN
t
ZH
CC
) sets the transconductance
= 0, the amplifier maintains
t
HZ
OUT
. See the Chip
100mV
The transconductance transfer function of the MAX9934
converts input differential voltage to an output current.
An output termination resistor, R
current to a voltage. In a large circuit board with multi-
ple ground planes and multiple current-measurement
rails spread across the board, traditional voltage-output
current-sense amplifiers become susceptible to
ground-bounce errors. These errors occur because the
local ground at the location of the current-sense amplifi-
er is at a slightly different voltage than the local ground
voltage at the ADC that is sampling the voltage. The
MAX9934 allows accurate measurements to be made
even in the presence of system ground noise. This is
achieved by sending the output information as a cur-
rent, and by terminating to the ADC ground.
A further advantage of current-output systems is the
flexibility in setting final voltage gain of the device.
Since the final voltage gain is user-controlled by the
choice of output termination resistor, it is easy to opti-
mize the monitored load current range to the ADC input
voltage range. It is no longer necessary to increase the
size of the sense resistor (also increasing power dissi-
pation) as necessary with fixed-gain, voltage-output
current-sense amplifiers.
Figure 3. Output Power-Up and Power-Down Time
V
V
CC
OUT
3.3V
0V
2.5V
Applications Information
Advantages of Current-Output
% FINAL VALUE
t
PU
OUT
t
PD
, then converts this
Architecture
100mV
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