Datasheet

ADS1114
2.0Vto5V
V
3kW
I C
2
1kWR
(2)
S
Load
(PGAGain=16)
256mVFS
FS=0.2V
G=4
-5V
R
(1)
49.9kW
3
5V
OPA335
0.1 FTypm
ADS1113
ADS1114
ADS1115
www.ti.com SBAS444B –MAY 2009–REVISED OCTOBER 2009
LOW-SIDE CURRENT MONITOR The ADS1113/4/5 are fabricated in a small-geometry,
low-voltage process. The analog inputs feature
Figure 38 shows a circuit for a low-side shunt-type
protection diodes to the supply rails. However, the
current monitor. The circuit monitors the voltage
current-handling ability of these diodes is limited, and
across a shunt resistor, which is sized as small as
the ADS1113/4/5 can be permanently damaged by
possible while giving a measurable output voltage.
analog input voltages that remain more than
This voltage is amplified by an OPA335 low-drift op
approximately 300mV beyond the rails for extended
amp, and the result is read by the ADS1114/5.
periods. One way to protect against overvoltage is to
place current-limiting resistors on the input lines. The
It is suggested that the ADS1114/5 be operated at a
ADS1113/4/5 analog inputs can withstand momentary
gain of 8. The gain of the OPA335 can then be set
currents as large as 100mA.
lower. For a gain of 16, the op amp should be set up
to give a maximum output voltage no greater than
If the ADS1113/4/5 are driven by an op amp with
0.256V. If the shunt resistor is sized to provide a
high-voltage supplies, such as ±12V, protection
maximum voltage drop of 50mV at full-scale current,
should be provided, even if the op amp is configured
the full-scale input to the ADS1114/5 is 0.2V.
so that it does not output out-of-range voltages. Many
op amps drift to one of the supply rails immediately
when power is applied, usually before the input has
stabilized; this momentary spike can damage the
ADS1113/4/5. This incremental damage results in
slow, long-term failure, which can be disastrous for
permanently installed, low-maintenance systems.
If an op amp or other front-end circuitry is used with
an ADS1113/4/5, performance characteristics must
be taken into account when designing the application.
(1) Pull-down resistor to allow accurate swing
to 0V.
(2) R
S
is sized for a 50mV drop at full-scale
current.
Figure 38. Low-Side Current Measurement
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Product Folder Link(s): ADS1113 ADS1114 ADS1115