Datasheet

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SINGLE-ENDED INPUTS
LOW-SIDE CURRENT MONITOR
1
2
3
6
5
4
V
IN-
V
IN+
SCL
GND
V
DD
SDA
ADS1000
V
DD
Output
Codes
0 2048-
FilterCapacitor
33pFto100pF
(typ.)
0V V
Single-Ended
-
DD
NOTES:(1)Pull-downresistortoallowaccurateswingto0V.
(2)R issizedfora50mVdropatfull-scalecurrent.
S
V
Load
R
S
(2)
1kW
G=12.5
-5V
OPA335
R
49.9k
3
W
(1)
FS=0.63V
5V
5V
11.5kW
ADS1000
I C
2
(PGAGain=8)
5VFS
ADS1000
SBAS357A – SEPTEMBER 2006 – REVISED OCTOBER 2007
amplifier, which can output fully differential signals.
This device can also help recover the lost bit noted
Although the ADS1000 has a fully differential input, it
previously for single-ended positive signals.
can easily measure single-ended signals. A simple
Level-shifting can also be performed using the
single-ended connection scheme is shown in
DRV134.
Figure 12 . The ADS1000 is configured for
single-ended measurement by grounding either of its
input pins, usually V
IN –
, and applying the input signal
to V
IN+
. The single-ended signal can range from
Figure 13 shows a circuit for a low-side shunt-type
– 0.2V to V
DD
+ 0.3V. The ADS1000 loses no linearity
current monitor. The circuit reads the voltage across
anywhere in its input range. Negative voltages cannot
a shunt resistor, which is sized as small as possible
be applied to this circuit because the ADS1000 inputs
while still giving a readable output voltage. This
can only accept positive voltages.
voltage is amplified by an OPA335 low-drift op-amp,
and the result is read by the ADS1000.
Figure 12. Measuring Single-Ended Inputs
The ADS1000 input range is bipolar differential with
respect to the reference, that is, V
DD
. The
Figure 13. Low-Side Current Measurement
single-ended circuit shown in Figure 12 covers only
half the ADS1000 input scale because it does not
It is recommended that the ADS1000 be operated at
produce differentially negative inputs; therefore, one
a gain of 8. The gain of the OPA335 can then be set
bit of resolution is lost. The DRV134 balanced line
lower. For a gain of 8, the op amp should be
driver can be employed to regain this bit for
configured to give a maximum output voltage of no
single-ended signals.
greater than 0.75V. If the shunt resistor is sized to
Negative input voltages must be level-shifted. A good
provide a maximum voltage drop of 50mV at
candidate for this function is the THS4130 differential
full-scale current, the full-scale input to the ADS1000
is 0.63V.
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