Texas Instruments TPA3251 User Manual page 11

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3.2 PWM Frequency Adjust
The TPA3251EVM offers a hardware-trimmed oscillator frequency by through the external control of the
FREQ_ADJ pin. Use the frequency adjust to reduce interference problems while using a radio receiver
tuned within the AM band and change the switching frequency from nominal values to lower values (see
Table 7). Choose these values such that the nominal- and the lower-value switching frequencies together
result in the fewest cases of interference throughout the AM band. Select the oscillator frequency based
on the value of the FREQ_ADJ resistor connected to GND in master mode.
Mode
MASTER MODE 600 kHz
MASTER MODE 500 kHz
MASTER MODE 450 kHz
For slave-mode operation, turn off the oscillator by pulling the FREQ_ADJ pin to 3.3 V. This action
configures the OSC_I/O pins as inputs, which are to be slaved from an external differential clock. In a
master and slave system, interchannel delay is automatically set up between the switching phases of the
audio channels, which can be illustrated by no idle channels switching at the same time. This setup does
not influence the audio output; rather, only the switch timing to minimize noise coupling between audio
channels through the power supply. In turn, this process optimizes audio performance and results in better
operating conditions for the power supply. The interchannel delay is setup for a slave device depending on
the polarity of the OSC_I/O connection, such that slave mode 1 is selected by connecting OSC_I/O of the
master device in phase with OSC_I/O of the slave device (+ to + and – to –), while slave mode 2 is
selected by connecting the OSC_I/Os out of phase (+ to – and – to +).
3.3 TPA3251EVM Overcurrent Adjust
The TPA3251EVM offers the ability for the user to change the current limit by changing R13 as well as
having two different protection modes, Cycle by Cycle Current Control (CB3C) and Latching Shutdown
(Latched OC). For CB3C operations, the resistance must be a value of 22 kΩ to 30 kΩ. For Latched OC
operations, the resistance must be a value of 47 kΩ to 64 kΩ. By default, the resistor R13 is 22 kΩ.
Table 8 shows a few resistance values and their corresponding OC threshold and OC protection mode.
3.4 TPA3251EVM Single-Ended and Differential Inputs
The TPA3251EVM supports both differential and SE inputs. For SE inputs, set either the J4 or J19 jumper
(or both) to the SE position so that the TPA3251EVM uses the
convert the SE input signal to differential to properly drive the differential inputs of the TPA3251 device.
Use input RCA jack J3 to provide INA and INB inputs. Use RCA jack J18 to provide INC and IND inputs
with SE inputs. For differential input operation, set either the J4 or J19 jumpers (or both) to the DIFF
position. The TPA3251EVM uses the NE5532 to buffer the differential input signal to the differential inputs
of the TPA3251 device. Use input RCA jack J3 to provide INA, RCA jack J14 to provide INB, RCA jack
J18 to provide INC, and RCA jack J15 to provide IND with differential inputs.
SLAU751 – November 2017
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Table 7. Frequency Adjust Master Mode Selection
Switching Frequency
600 kHz
500 kHz
450 kHz
Table 8. Overcurrent Protection Selection
OC_ADJ Resistor
Protection Mode
Value
22 kΩ
24 kΩ
27 kΩ
30 kΩ
47 kΩ Latched OC
51 kΩ Latched OC
56 kΩ Latched OC
64 kΩ Latched OC
Copyright © 2017, Texas Instruments Incorporated
Resistor to GND
10 kΩ
20 kΩ
30 kΩ
OC Threshold
CB3C 16.3 A
CB3C 15.1 A
CB3C 13.5 A
CB3C 12.3 A
16.3 A
15.1 A
13.5 A
12.3 A
NE5532 operational amplifier (op amp) to
Hardware Configuration
Pin Configuration
3 to 4
5 to 6
7 to 8
TPA3251 Evaluation Module
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