AM3703CUS datasheet(157/280 Pages) TI

157 / 280 page

AM3715, AM3703

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SPRS616F

– JUNE 2010 – REVISED AUGUST 2011

5.7

External Component Value Choice

The output current IDACOUT appearing at the output of the 10-bit DAC is a function of both the input code

DAC_CODE (ranging from 0 to 1023) and IDACMAX and can be expressed as:

IDACOUT = IREF * (DAC_CODE / 120) (1)

The maximum output current IDACMAX from the DAC is given by:

IDACMAX = IREF * 1023 / 120 (2)

The reference current, IREF, is set by a combination of internal and external resistors in series, RREF, and

an internal reference voltage, VREF, and is given by:

IREF = VREF / RREF (3)

Typically, VREF = 0.55 V and RREF = 9.4 kΩ in TVOUT High-Swing mode.

The video signal voltage at cvideo_out1 and cvideo_out2 nodes can be written as (excluding the offset

voltage):

VTVOUT = 35 * RLOAD * IDACMAX * (1 – DAC_CODE / 1023) (4)

Figure 5-6 shows the cvideo_out1 and cvideo_out2 transfer function. Regarding the typical composite

video signal levels versus the DAC input code, for more information on code range definition, see

Figure 5-4.

Regarding the typical values of the typical values for Rout1/2 and Rset resistors, as well for Cout capacitor,

for different modes of the TV display interface, see the Display Subsystem / Display Subsystem

Environment / TV Display Support section of AM/DM37x Technical Reference Manual (literature number

SPRUGN4).

Figure 5-6. cvideo_out1 and cvideo_ou2 Transfer Function

NOTE

The dc levels (Voffset) will be shifted due to process variations.

Video DAC Specifications

157

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