ISL28191_0808 Datasheet, PDF (10/16 Pages) Intersil Corporation – Low Distortion Rail-to-Rail Output, Op Amp

ISL28191, ISL28291
Pin Descriptions (Continued)
ISL28191
ISL28191 ISL28291 ISL28291
ISL28291
PIN
(6 Ld SOT-23) (6 Ld µTDFN) (8 Ld SOIC) (10 Ld MSOP) (10 Ld µTQFN) NAME
FUNCTION
1
1
OUT Output
1 (A)
1 (A)
10 (A)
OUT_A
7 (B)
9 (B)
8 (B)
OUT_B
EQUIVALENT CIRCUIT
V+
OUT
6
6
8
10
9
5
5
N/A
5 (A)
4 (A)
6 (B)
5 (B)
Applications Information
Product Description
The ISL28191 and ISL28291 are voltage feedback operational
amplifiers designed for communication and imaging
applications requiring low distortion, very low voltage and
current noise. Both parts feature high bandwidth while drawing
moderately low supply current. They use a classical
voltage-feedback topology, which allows them to be used in a
variety of applications where current-feedback amplifiers are
not appropriate because of restrictions placed upon the
feedback element used with the amplifier.
Enable/Power-Down
The ISL28191 and ISL28291 amplifiers are disabled by
applying a voltage greater than 2V to the EN pin, with
respect to the V- pin. In this condition, the output(s) will be in
a high impedance state and the amplifier(s) current will be
reduced to 13µA/Amp. By disabling the part, multiple parts
can be connected together as a MUX. The outputs are tied
together in parallel and a channel can be selected by the EN
pin. The EN pin also has an internal pull-down. If left open,
the EN pin will pull to the negative rail and the device will be
enabled by default.
Input Protection
All input 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. Both parts have
additional back-to-back diodes across the input terminals (as
shown in Figure 29). In pulse applications where the input
Slew Rate exceeds the Slew Rate of the amplifier, the
possibility exists for the input protection diodes to become
forward biased. This can cause excessive input current and
distortion at the outputs. If overdriving the inputs is necessary,
the external input current must never exceed 5mA. An
V-
Circuit 2
V+ Positive supply
EN Enable BAR
V+
EN_A pin internal
EN_B pull-down; Logic
“1” selects the
EN
disabled state;
Logic “0” selects
V-
the enabled
state.
Circuit 3
external series resistor may be used to limit the current, as
shown in Figure 29.
-
R
+
FIGURE 29. LIMITING THE INPUT CURRENT TO LESS THAN
5mA
Using Only One Channel
The ISL28291 is a dual channel op amp. If the application
only requires one channel when using the ISL28291, the
user must configure the unused channel to prevent it from
oscillating. Oscillation can occur if the input and output pins
are floating. This will result in higher than expected supply
currents and possible noise injection into the channel being
used. The proper way to prevent this oscillation is to short
the output to the negative input and ground the positive input
(as shown in Figure 30).
-
+
FIGURE 30. PREVENTING OSCILLATIONS IN UNUSED
CHANNELS
Power Supply Bypassing and Printed Circuit
Board Layout
As with any high frequency device, good printed circuit
board layout is necessary for optimum performance. Low
impedance ground plane construction is essential. Surface
mount components are recommended, but if leaded
components are used, lead lengths should be as short as
possible. The power supply pins must be well bypassed to
10
FN6156.7
August 11, 2008