OMAP3530ECBC72 datasheet(152/264 Pages) TI1

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5.4 External Component Value Choice

OMAP3530/25 Applications Processor

SPRS507F – FEBRUARY 2008 – REVISED OCTOBER 2009

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Because the DAC PSRR deteriorates at a rate of 20 dB/dec after 100 kHz, it is highly recommended to

have vdda_dac low pass filtered (proper decoupling) (see the illustrated application: Section 5.4, External

Component Value Choice).

The full-scale output voltage VOUTMAX is regulated by the reference amplifier, and is set by an internal

resistor RSET. IOUTMAX can be expressed as:

IOUTMAX = IREF /8 * (63 + 15/16)

Where:

VREF = 0.55V

IREF = VREF/ (2* RSET)

The output current IOUT appearing at DAC output is a function of both the input code and IOUTMAX and can

be expressed as:

IOUT = (DAC_CODE/1023) * IOUTMAX

Where:

DAC_CODE = 0 to 1023 is the DAC input code in decimal.

The output voltage is:

VOUT = IOUT *N* RCABLE

Where:

(N = amplifier gain = 21)

RCABLE = 75 Ω (cable typical impedance)

The TV-out buffer requires a per channel external resistors: ROUT1/2. The equation below can be used to

select different resistor values (if necessary):

ROUT = (N+1) RCABLE = 1650 Ω

Recommended parameter values are:

Table 5-7. Video DAC – Recommended External Components Values

Recommended Value

UNIT

CBG

100

ROUT1/2

1650

Ω

In order to limit the reference noise bandwidth and to suppress transients on VREF, it is necessary to

connect a large decoupling capacitor BG) between the tv_vref and vssa_dac pins.

VIDEO DAC SPECIFICATIONS

152

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OMAP3530ECBC72 Datasheet(PDF) 152 Page - Texas Instruments