APPLICATION INFORMATION
FULLY DIFFERENTIAL AMPLIFIER
Advantages of Fully Differential Amplifiers
SHORT CIRCUIT AUTO-RECOVERY
SHUTDOWN BEHAVIOR
COMPONENT SELECTION
www.ti.com.............................................................................................................................................................................................. SLOS589 – OCTOBER 2008
The TPA2036D1 is a fully differential amplifier with differential inputs and outputs. The fully differential amplifier
consists of a differential amplifier and a common-mode amplifier. The differential amplifier ensures that the
amplifier outputs a differential voltage on the output that is equal to the differential input times the gain. The
common-mode feedback ensures that the common-mode voltage at the output is biased around VDD/2 regardless
of the common-mode voltage at the input. The fully differential TPA2036D1 can still be used with a single-ended
input; however, the TPA2036D1 should be used with differential inputs when in a noisy environment, like a
wireless handset, to ensure maximum noise rejection.
Input-coupling capacitors not required:
–
The fully differential amplifier allows the inputs to be biased at voltage other than mid-supply. For example,
if a codec has a midsupply lower than the midsupply of the TPA2036D1, the common-mode feedback
circuit will adjust, and the TPA2036D1 outputs will still be biased at midsupply of the TPA2036D1. The
inputs of the TPA2036D1 can be biased from 0.5 V to VDD –0.8 V. If the inputs are biased outside of that
range, input-coupling capacitors are required.
Midsupply bypass capacitor, C
(BYPASS), not required:
–
The fully differential amplifier does not require a bypass capacitor. This is because any shift in the
midsupply affects both positive and negative channels equally and cancels at the differential output.
Better RF-immunity:
–
GSM handsets save power by turning on and shutting off the RF transmitter at a rate of 217 Hz. The
transmitted signal is picked-up on input and output traces. The fully differential amplifier cancels the signal
much better than the typical audio amplifier.
When a short circuit event happens, the TPA2036D1 goes to shutdown mode and tries to reactivate itself after
40
s. This auto-recovery will continue until the short circuit event is removed. With the recommended PCB
layout, this feature can protect the device without affecting the device's long term reliability.
The input of TPA2036D1 has ESD protection circuitry. During shutdown, the maximum allowed voltage at input
and output pins is -0.3 V to VDD +0.3 V.
Figure 27 shows the TPA2036D1 typical schematic with differential inputs and
Figure 28 shows the TPA2036D1
with differential inputs and input capacitors, and
Figure 29 shows the TPA2036D1 with single-ended inputs.
Differential inputs should be used whenever possible because the single-ended inputs are much more
susceptible to noise. X5R or X7R with ±10% or better dielectric material is required.
Table 1. Typical Component Values
REF DES
VALUE
EIA SIZE
MANUFACTURER
PART NUMBER
RI
150 k
(±1%)
0402
Panasonic
ERJ-2RKF1503X
CS
1
F (X5R, ±10%)
0402
Murata
GRM155R61A105KE
15D
CI
(1)
3.3 nF (X5R, ±10%)
0201
Murata
GRM033R61A332KA
01D
(1)
CI is only needed for single-ended input or if VICM is not between 0.5 V and VDD – 0.8 V. CI = 3.3 nF
(with RI = 150 k) gives a high-pass corner frequency of 321 Hz.
Copyright 2008, Texas Instruments Incorporated
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