THS4524-EP_17 Datasheet, PDF (28/48 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

THS4524-EP
SBOS609A – JUNE 2012 – REVISED AUGUST 2013
Figure 63 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 63. V_OCM Input Circuit
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Single-Supply Operation
To facilitate testing with common lab equipment, the
THS4524EVM 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 64 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
Typical Performance Variation with Supply
Voltage
The THS4524 provides excellent performance across
the specified power-supply range of 2.5 V to 5.5 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. Table 3 shows
the typical variation to be expected in these key
performance parameters.
Figure 64. THS4524 DC-Coupled Single-Supply
with Single-Ended Inputs
The input common-mode voltage range of the
THS4524 is designed to include the negative supply
voltage. in the circuit shown in Figure 64, 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.
Table 3. Typical Performance Variation versus Power-Supply Voltage
PARAMETER
–3-dB Small-signal bandwidth
Slew rate (2-V step)
Harmonic distortion at 1 MHz, 2 V_PP, R_L = 1 kΩ
xxxSecond harmonic
xxxThird harmonic
Open-loop gain
Linear output current drive
V_S = 5 V
145 MHz
490 V/μs
–85 dBc
–91 dBc
119 dB
55 mA
V_S = 3.3 V
135 MHz
420 V/μs
–85 dBc
–90 dBc
116 dB
35 mA
V_S = 2.5 V
125 MHz
210 V/μs
–84 dBc
–88 dBc
115 dB
24 mA
28
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