PCM1750UG4 datasheet(13/21 Pages) TI

13 / 21 page

PCM1750

POWER SUPPLY REJECTION

Because of the architecture of the PCM1750, power supply

rejection varies with input signal size. The spec table value

is expressed in the relative terms of percent of VIN per

percent change of the supply voltage. The PSR versus

Frequency plot in the Typical Performance Curves show

PSR expressed versus an increase in power supply ripple

frequency.

PERFORMANCE OVER TEMPERATURE

Specification Temperatures

All critical specifications are tested at 25

°C. The drift

specification temperature range is from 0

°C to +70°C. The

PCM1750 will operate over the wider temperature range of

–40

°C to +85°C.

Gain and Offset Drift

Although the PCM1750 is primarily meant for use in dy-

namic applications, specifications are also given for more

traditional DC drift parameters such as temperature gain and

offset drift. The primary cause of drift in the PCM1750 is the

bandgap reference. Much lower gain drift can be realized if

necessary by using any circuit similar to the external refer-

ence circuits shown in Figure 8. Also, refer to the Typical

Performance Curves of VREF Output versus Temperature.

Dynamic Performance

Dynamic performance is predominated by the absolute lin-

earity of the PCM1750. Because of the excellent ratio

tracking versus temperature of poly-poly capacitors, there is

virtually no change in dynamic performance of the converter

over temperature (primarily THD+N). The dynamic specifi-

cations over temperature cannot be guaranteed, however, as

they are not 100% tested.

INSTALLATION

ANTI-ALIASING FILTER

To prevent unwanted input signals from being aliased into

the passband of the converter, it is necessary to suppress all

out of band signals above 1/2 the sampling frequency of the

ADC by using a low-pass filter. The requirement for an anti-

aliasing filter, however, can be reduced by using oversampling

techniques. By raising the sample rate of the converter by a

factor of 2 or even 4, the roll off of the anti-aliasing filter can

be reduced. In Figure 9, a 6th order, linear-phase, anti-

aliasing filter is implemented using low-cost dual audio op

amps. This filter will suppress frequencies above 96kHz by

80dB. For many applications a 4th or 2nd order anti-aliasing

filter will be adequate when using the PCM1750 in the 4x

oversampling mode.

FIGURE 7. PCM1750 Connection Diagram.

+ 10µF*

47µF

0.1µF

150k

Ω

25k

Ω

47k

Ω

25k

Ω

10µF*

47µF

10µF*

+5V

–5V

= Connect directly to ground plane

Optional External Adjust

–V

SOUT Left

Ext Clk In

DCOM

ACOM

DCOM

Convert

SOUT Right

–V

Offset Adj Left

MSB Adj Left

Left

Ref In Left

Ref Out Left

ACOM

Ref Com

Ref Bypass

ACOM

Ref Out Right

Ref In Right

Right

MSB Adj Right

Offset Adj Right

150k

Ω

25k

Ω

47k

Ω

25k

Ω

Optional External Adjust

Ω

10µF*

220pF

150

Ω

220pF

47k

Ω

0.01µF

47k

Ω

(low

leakage,

ceramic)

* High quality tantalum.

150

Ω

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