OMAP3530ECUS Datasheet, PDF (152/264 Pages) Texas Instruments – OMAP3530/25 Applications Processor: OMAP 3 Architecture

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).
5.4 External Component Value Choice
The full-scale output voltage V_OUTMAX is regulated by the reference amplifier, and is set by an internal
resistor R_SET. I_OUTMAX can be expressed as:
I_OUTMAX = I_REF /8 * (63 + 15/16)
Where:
V_REF = 0.55V
I_REF = V_REF/ (2* R_SET)
The output current I_OUT appearing at DAC output is a function of both the input code and I_OUTMAX and can
be expressed as:
I_OUT = (DAC_CODE/1023) * I_OUTMAX
Where:
DAC_CODE = 0 to 1023 is the DAC input code in decimal.
The output voltage is:
V_OUT = I_OUT *N* R_CABLE
Where:
(N = amplifier gain = 21)
R_CABLE = 75 Ω (cable typical impedance)
The TV-out buffer requires a per channel external resistors: R_OUT1/2. The equation below can be used to
select different resistor values (if necessary):
R_OUT = (N+1) R_CABLE = 1650 Ω
Recommended parameter values are:
Table 5-7. Video DAC – Recommended External Components Values
C_BG
R_OUT1/2
Recommended Value
100
1650
UNIT
nF
Ω
In order to limit the reference noise bandwidth and to suppress transients on V_REF, it is necessary to
connect a large decoupling capacitor _BG) between the tv_vref and vssa_dac pins.
152 VIDEO DAC SPECIFICATIONS
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