THS4521-HT_15 Datasheet, PDF (19/27 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT,RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

THS4521-HT
www.ti.com
Figure 36 represents the V_OCM input. The internal
V_OCM circuit has typically 23 MHz of –3 dB bandwidth,
which is required for best performance, but it is
intended to be a dc bias input pin. A 0.22-μF bypass
capacitor is recommended on this pin to reduce
noise. The external current required to overdrive the
internal resistor divider is given approximately by the
formula in Equation 2:
I_EXT =
2V_OCM - (V_S+ - V_S-)
50 kW
where:
• V_OCM is the voltage applied to the V_OCM pin
(2)
V_S+
To internal
V_OCM circuit
100 kW
100 kW
I_EXT
V_OCM
V_S-
Figure 36. V_OCM Input Circuit
Typical Performance Variation with Supply
Voltage
The THS4521 provides excellent performance across
the specified power-supply range of 2.5 V to 3.3 V
with only minor variations. The input and output
voltage compliance ranges track with the power
supply in nearly a 1:1 correlation. Other changes can
be observed in slew rate, output current drive, open-
loop gain, bandwidth, and distortion.
SBOS548D – APRIL 2011 – REVISED MAY 2012
Single-Supply Operation
To facilitate testing with common lab equipment, the
THS4521EVM allows for split-supply operation; most
of the characterization data presented in this data
sheet is measured using split-supply power inputs.
The device can easily be used with a single-supply
power input without degrading performance.
Figure 37 shows a dc-coupled single-supply circuit
with single-ended inputs. This circuit can also be
applied to differential input sources.
V_IN+
PD Control
Optional;
installed to
balance
impedance seen
at V_IN+
R_G
R_IT
R_F
V_S+
PD
0.22 mF
THS452x
V_S-
V_OCM
R_G
R_F
R_IT
R_O
V_OUT-
R_O
V_OUT+
V_OCM Control
0.22 mF
Figure 37. THS4521 DC-Coupled Single-Supply
with Single-Ended Inputs
The input common-mode voltage range of the
THS4521 is designed to include the negative supply
voltage. In the circuit shown in Figure 37, the signal
source is referenced to ground. V_OCM is set by an
external control source or, if left unconnected, the
internal circuit defaults to midsupply. Together with
the input impedance of the amplifier circuit, R_IT
provides input termination, which is also referenced to
ground.
Note that R_IT and optional matching components are
added to the alternate input to balance the
impedance at signal input.
Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Link(s): THS4521-HT
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