Datasheet

I =
IA
orV =
IA
2
R
GAIN
V
IN
2
R
GAIN
R
IA
V
IN
XTR300
SBOS336C –JUNE 2005– REVISED JUNE 2011 www.ti.com
EXTERNALLY-CONFIGURED MODE: OPA AND IA
It is possible to use the precision of the operational amplifier (OPA) and instrumentation amplifier (IA)
independently from each other by configuring the digital control pins (M1 high). In this mode, the IA output
current is routed to IA
OUT
and the copy of the OPA output current is routed to I
MON
, as shown in Figure 4.
This mode allows external configuration of the analog signal routing and feedback loop.
The current output IA has high input impedance, low offset voltage and drift, and very high common-mode
rejection ratio. An external resistor (R
IA
) can be used to convert the output current of the IA (I
IA
) to an output
voltage. The gain is given by:
(5)
The OPA provides low drift and high voltage output swing that can be used like a common operational amplifier
by connecting a feedback network around it. In this mode, the copy of the output current is available at the I
MON
pin (it includes the current into the feedback network). It provides an output current limit for protection, which can
be set between two ranges by M2. The error flag indicates an overcurrent condition, as well as indicating driving
the output into the supply rails.
Alternatively, the feedback can be closed through the I
MON
pin to create a precise voltage-to-current converter.
DRIVER OUTPUT DISABLE
The OPA output (DRV) can be switched to a high-impedance mode by driving the OD control pin low. This input
can be connected to the over-temperature flag, EF
OT
, and a pull-up resistor to protect the IC from
over-temperature by disconnecting the load.
The output disable mode can be used to sense and measure the voltage at the IA input pins without loading from
the DRV output. This mode allows testing of any voltage present at the I/O connector. However, consider the
bias current of the IA input pins.
The digital control inputs, M1 and M2, set the four operation modes of the XTR300 as shown in Table 1. When
M1 is asserted low, M2 determines voltage or current mode and the corresponding appropriate current limit (I
SC
)
setting. When M1 is high, the internal feedback connections are opened; IA
OUT
and I
MON
are both connected to
the output pins; and M2 only determines the current limit (I
SC
) setting.
M1 and M2 are pulled low internally with 1μA. Terminate these two pins to avoid noise coupling. Output disable
(OD) is internally pulled high with approximately 1μA. When connecting OD to EF
OT
, a 2.2kΩ pull-up resistor is
recommended.
Table 1. Summary of Configuration Modes
(1)
M1 M2 MODE DESCRIPTION
L L V
OUT
Voltage Output Mode, I
SC
= 20mA
L H I
OUT
Current Output Mode, I
SC
= 32mA
H L Ext IA and I
MON
on ext. pins, I
SC
= 20A
H H Ext IA and I
MON
on ext. pins, I
SC
= 32mA
(1) OD is a control pin independent of M1 or M2.
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