Datasheet

AM3517, AM3505
www.ti.com SPRS550E –OCTOBER 2009–REVISED MARCH 2013
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) (1)
Where:
V
REF
= 0.5V (2)
I
REF
= V
REF
/R
SET
(3)
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
(4)
Where:
DAC_CODE = 0 to 1023 is the DAC input code in decimal. (5)
The output voltage is:
V
OUT
= I
OUT
*N* R
CABLE
(6)
Where:
(N = amplifier gain = 21) (7)
R
CABLE
Ω (cable typical impedance) (8)
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
= 1650Ω (9)
Recommended parameter values are:
Table 5-7. Video DAC Recommended External Components Values
Recommended Value UNIT
C
BG
100 nF
R
OUT1/2
1650 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.
Copyright © 2009–2013, Texas Instruments Incorporated Video DAC Specifications 105
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