Texas Instruments PCM5142 Evaluation Module PCM5142EVM-U PCM5142EVM-U Fiche De Données
Codes de produits
PCM5142EVM-U
SLAS759A – AUGUST 2012 – REVISED SEPTEMBER 2012
Analog Outputs
The PCM514x devices include a two-channel DAC, with single-ended outputs. The full-scale output voltage is
2.1V
2.1V
rms
with ground center output. A dc-coupled load is supported in addition to an ac-coupled load, if the load
resistance conforms to the specification. The PCM514x DAC outputs on the OUTL and OUTR terminals have
market-leading low out-of-band noise, which offer up to 20dB lower out-of-band noise compared with existing
DAC technology.
market-leading low out-of-band noise, which offer up to 20dB lower out-of-band noise compared with existing
DAC technology.
Most applications require an external low-pass RC filter (470
Ω
+ 2.2nF) to provide sufficient out-of-band noise
rejection. This RC filter provides the added advantage of improved protection against ESD damage. Further
discussion of DAC post-filter circuits is provided in the PCM514x Application Reference Guide, SLAU345.
discussion of DAC post-filter circuits is provided in the PCM514x Application Reference Guide, SLAU345.
Voltage Reference and Ouptut Levels
The PCM514x has an internal, fixed band-gap reference voltage, with default operation in VREF mode. No
external decoupling capacitor is required for this mode. VREF mode provides 2.1V
external decoupling capacitor is required for this mode. VREF mode provides 2.1V
rms
full-scale output at both
AVDD levels.
The PCM514x can be operated with a common-mode voltage output (VCOM mode) at the VCOM pin by setting
Page 1, Register 1, D(0) to 1. In this mode, an external decupling capacitor is required.
Page 1, Register 1, D(0) to 1. In this mode, an external decupling capacitor is required.
When using this DAC in VREF mode, the output-signal voltage is independent of the power-supply voltage: The
D/A conversion gain in VREF mode yields a 2.1V
D/A conversion gain in VREF mode yields a 2.1V
rms
output voltage with a digital full-scale input. However, in
VREF mode, an output waveform may clip due to the limitations that may be present in the analog power supply
voltage. On the other hand, the full-scale output voltage in VCOM mode is proportional to the analog power
supply AVDD. Example, (2.1 × AVDD / 3.3) V
voltage. On the other hand, the full-scale output voltage in VCOM mode is proportional to the analog power
supply AVDD. Example, (2.1 × AVDD / 3.3) V
rms
.
Mode Switching Sequence, From VREF Mode to VCOM Mode
Following register setting sequence is recommended for changing VREF mode to VCOM mode.
1. Page 0 / Register 2
RQST = 1: Standby mode
2. Page 1 / Register 8
RCMF = 1: Fast ramp up
→
on
3. Page 1 / Register 9
VCPD = 0: VCOM is power on
4.
Wait 3ms with external capacitor = 1µF
5. Page 1 / Register 8
RCMF = 0: Fast ramp up
→
off
6. Page 1 / Register 1
OSEL = 1: VCOM mode
7. Page 0 / Register 2
RQST = 0: Normal mode
Copyright © 2012, Texas Instruments Incorporated
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