THS4211 Datasheet, PDF (21/50 Pages) Texas Instruments – LOW-DISTORTION HIGH-SPEED VOLTAGE FEEDBACK AMPLIFIER

THS4211
THS4215
www.ti.com ................................................................................................................................... SLOS400E – SEPTEMBER 2002 – REVISED SEPTEMBER 2009
SINGLE-SUPPLY OPERATION
The THS4211 is designed to operate from a single
5-V to 15-V power supply. When operating from a
single power supply, care must be taken to ensure
the input signal and amplifier are biased appropriately
to maximize output voltage swing. The circuits shown
in Figure 77 demonstrate methods to configure an
amplifier for single-supply operation.
+V_S
50 Ω Source
V_I
R_T 49.9 Ω
+
THS4211
_
+V_S
R_f
2
R_g
392 Ω
392 Ω
+V_S
2
50 Ω Source
R_g
V_I
392 Ω
57.6 Ω R_T
+V_S
+V_S
2
2
R_f
392 Ω
V_S
_
THS4211
+
V_O
499 Ω
V_O
499 Ω
Figure 77. DC-Coupled Single Supply Operation
Note that this power-down functionality is just that;
the amplifier consumes less power in power-down
mode. The power-down mode is not intended to
provide a high- impedance output. In other words, the
power-down functionality is not intended to allow use
as a 3-state bus driver. When in power-down mode,
the impedance looking back into the output of the
amplifier is dominated by the feedback and gain
setting resistors, but the output impedance of the
device itself varies depending on the voltage applied
to the outputs.
The time delays associated with turning the device on
and off are specified as the time it takes for the
amplifier to reach 50% of the nominal quiescent
current. The time delays are on the order of
microseconds because the amplifier moves in and out
of the linear mode of operation in these transitions.
Power-Down Reference Pin Operation
In addition to the power-down pin, the THS4215 also
features a reference pin (REF) which allows the user
to control the enable or disable power-down voltage
levels applied to the PD pin. Operation of the
reference pin as it relates to the power-down pin is
described below.
In most split-supply applications, the reference pin will
be connected to ground. In some cases, the user
may want to connect it to the negative or positive
supply rail. In either case, the user needs to be aware
of the voltage level thresholds that apply to the
power-down pin. The table below illustrates the
relationship between the reference voltage and the
power-down thresholds.
Saving Power with Power-Down
Functionality and Setting Threshold Levels
with the Reference Pin
The THS4215 features a power-down pin (PD) which
lowers the quiescent current from 19-mA down to
650-µA, ideal for reducing system power.
The power-down pin of the amplifiers defaults to the
positive supply voltage in the absence of an applied
voltage, putting the amplifier in the power-on mode of
operation. To conserve power, the amplifier is turned
off by driving the power-down pin towards the
negative rail. The threshold voltages for power-on
and power-down are relative to the supply rails, and
are given in the specification tables. Above the
Enable Threshold Voltage, the device is on. Below
the Disable Threshold Voltage, the device is off.
Behavior between these threshold voltages is not
specified.
REFERENCE
VOLTAGE
V_S– to 0.5 (V_S– + V_S+)
0.5 (V_S– + V_S+) to V_S+
POWER-DOWN PIN VOLTAGE
DEVICE
DISABLED
DEVICE
ENABLED
≤ Ref + 1.0 V
≥ Ref + 1.8 V
≤ Ref – 1.5 V
≥ Ref – 1 V
The recommended mode of operation is to tie the
reference pin to mid-rail, thus setting the threshold
levels to mid-rail +1.0 V and midrail +1.8 V.
NO. OF CHANNELS
PACKAGES
Single (8-pin)
THS4215D, THS4215DGN, and
THS4215DRB
Copyright © 2002–2009, Texas Instruments Incorporated
Product Folder Link(s): THS4211 THS4215
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