ISL28270_0708 Datasheet, PDF (14/18 Pages) Intersil Corporation – Dual and Quad Channel Micropower, Single Supply, Rail-to-Rail Input and Output (RRIO) Instrumentation Amplifiers

ISL28270, ISL28273, ISL28470
Pin Descriptions (Continued)
ISL28270 ISL28273 ISL28470
16 Ld QSOP 16 Ld QSOP 28 Ld QSOP PIN NAMES
8
8
22
V-
1, 9
1, 9
14,15
NC
EQUIVALENT
CIRCUIT
PIN FUNCTION
Circuit 4
Negative Supply terminal shared by all channels. Grounded for single
supply operation.
No Connect, pins can be left floating or grounded
IN-
FB-
CIRCUIT 1A
IN-
FB-
V₊
IN+
FB+
V_-
V₊
IN+
FB+
V_-
LOGIC
PIN
V₊
V_-
CIRCUIT 2
V₊
OUT
V_-
CIRCUIT 3
V₊
CAPACITIVELY
COUPLED
ESD CLAMP
V_-
CIRCUIT 4
CIRCUIT 1B
Application Information
Product Description
The ISL28270 and ISL28273 are dual channel micro-power
instrumentation amplifiers (in-amps) and the ISL28470 is a
quad channel which deliver rail-to-rail input amplification and
rail-to-rail output swing. The in-amps also deliver excellent
DC and AC specifications while consuming only about 60µA
per channel. Because the independent pair of feedback
terminals set the gain and adjust the output zero level, the
ISL28270, ISL28273 and ISL28470 achieve high CMRR
regardless of the tolerance of the gain setting resistors. The
ISL28270 and ISL28470 are internally compensated for a
minimum gain of 100. The ISL28273 is internally
compensated for a minimum gain of 10.
EN pins are available to independently enable or disable a
channel. When all channels are off, current consumption is
down to typically 4µA on the duals (ISL28270 and
ISL28273), and 10µA on the quad (ISL28470).
Input Protection
All input terminals and feedback terminals have internal ESD
protection diodes to both positive and negative supply rails,
limiting the input voltage to within one diode beyond the
supply rails. Input signals originating from low impedance
sources should have current limiting resistors in series with
the IN+ and IN- pins to prevent damaging currents during
power supply sequencing and other transient conditions.
The ISL28270 and ISL28470 have additional back-to-back
diodes across the input terminals and also across the
feedback terminals. If overdriving the inputs is necessary,
the external input current must never exceed 5mA. External
series resistors may be used as an external protection to
limit excessive external voltage and current from damaging
the inputs. On the other hand, the ISL28273 has no clamps
to limit the differential voltage on the input terminals allowing
higher differential input voltages at lower gain applications. It
is recommended, however, that the terminals of the
ISL28273 are not overdriven beyond 1V to avoid offset drift.
Input Stage and Input Voltage Range
The input terminals (IN+ and IN-) of the in-amps are a single
differential pair of bipolar PNP devices aided by an Input Range
Enhancement Circuit, IREC, to increase the headroom of
operation of the common-mode input voltage. The feedback
terminals (FB+ and FB-) also have a similar topology. As a
result, the input common-mode voltage range is rail-to-rail
regardless of the feedback terminal settings and regardless of
the gain settings. They are able to handle input voltages that
are at or slightly beyond the supply and close to ground making
these in-amps well suited for single 5V down to 2.4V supply
systems. There is no need to bias the common-mode input to
achieve symmetrical input voltage. It is recommended however
that the common-mode input be biased at least 10mV above
the negative supply rail to achieve top performance. See “Input
Bias Cancellation/Compensation” on page 15.
The IREC enables rail-to-rail input amplification without the
problems usually associated with the dual differential stage
topology. The IREC ensures that there are no drastic
changes in offset voltage over the entire range of the input.
See Input Offset Voltage vs Common-Mode Input Voltage on
page 8. IREC also cures the abrupt change and even
reverse polarity of the input bias current over the whole
14
FN6260.4
August 3, 2007