THS4552 Datasheet, PDF (53/71 Pages) Texas Instruments – Dual-Channel, Low-Noise, Precision, 150-MHz, Fully Differential Amplifier

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THS4552
SBOS831 – DECEMBER 2016
VS+
+
2.5 V
±
VS-
-2.5 V ⁺
±
LM27762
Supplies
6.2 mA
VS-
402
CF1
2.4 nF _4.4
RF1
750
VS+
THS4552 Wideband,
Fully Differential Amplifier
PCM1792A
Complementary Current
Output DAC
20 nF
VOCM
±
+
FDA
±
+
PD
VS- ^VS+
6.2 mA
402
VS-
RF2
750
CF2 ^4.4
2.4 nF
Copyright © 2016, Texas Instruments Incorporated
Figure 93. PCM1792A DAC Output Driver
10.2.2.1 Design Requirements
To implement a differential transimpedance output interface to the PCM1792A DAC, the following requirements
must be met:
• The center current of the DAC must be considered to hold the DAC output voltage at ground. Using an FDA
controls the output side common-mode voltage, but the input common-mode voltage must also be controlled
to ground.
• A direct means of sinking the center current is to add a pulldown resistor at the DAC outputs to a negative
supply. Generating a ±2.5-V supply for this current sink requirement and the THS4552 is accomplished with
the LM27762.
• The transimpedance gain can be set using the feedback resistors of the THS4552 FDA. These resistors are
very flexible, but when set, the bandwidth in this stage is set to 88 kHz using a feedback capacitor in parallel
with the resistive gain element.
• When the feedback capacitor is set, a differential input capacitor is added to increase the high-frequency
noise gain for the overall loop gain stability.
• These frequency response control capacitors interact with the inductive open-loop output impedance to form
a high-frequency resonance. Adding a small series resistor to the feedback capacitor paths reduces this
effect.
10.2.2.2 Detailed Design Procedure
Proceed with this design using the techniques described in the Design for Wideband Differential Transimpedance
DAC Output application note (SBAA150):
• Generate the bipolar balanced supplies using the LM27662.
• Set the THS4552 output common-mode voltage at midsupply by grounding the VOCM pin.
• Control the input pin operating voltage by sinking the center current out of the DAC to the –2.5-V supply with
precision 402-Ω resistors.
• Set the gain for the complementary current output signal from the DAC by selecting the feedback resistor to
be 750 Ω. Set this resistor to keep the resulting output swing to be less than the available 9-V_PP differential
swing.
• Control the bandwidth in this differential transimpedance stage to 88 kHz using the 2.4-nF feedback capacitor
on each side.
• Increase the high-frequency noise gain to 17.7 V/V by adding a differential input capacitor of 20 nF.
• Isolate these feedback capacitors with a series 4.4-Ω resistor in series with the feedback capacitors.
Copyright © 2016, Texas Instruments Incorporated
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