Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsData collecting ICsData acquisition IC - AD converter (ADC) External , Internal HTQFP 80

ADS5281

ADS5282

SBAS397I –DECEMBER 2006–REVISED JUNE 2012

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All three drive strengths (bit clock, frame clock, and data) are programmed using sets of three bits. Table 5

shows an example of how the drive strength of the bit clock is programmed (the method is similar for the frame

clock and data drive strengths).

Table 5. Bit Clock Drive Strength

(1)

ILVDS_LCLK<2> ILVDS_LCLK<1> ILVDS_LCLK<0> LVDS DRIVE STRENGTH FOR LCLK

AND LCLK

0 0 0 3.5mA (default)

0 0 1 2.5mA

0 1 0 1.5mA

0 1 1 0.5mA

1 0 0 7.5mA

1 0 1 6.5mA

1 1 0 5.5mA

1 1 1 4.5mA

(1) Current settings lower than 1.5mA are not recommended.

LVDS INTERNAL TERMINATION PROGRAMMABILITY

ADDRESS

IN HEX D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 NAME

X EN_LVDS_TERM

1 X X X TERM_LCLK<2:0>

1 X X X TERM_FRAME<2:0>

1 X X X TERM_DAT<2:0>

The LVDS buffers have high-impedance current sources driving the outputs. When driving traces whose

characteristic impedance is not perfectly matched with the termination impedance on the receiver side, there may

be reflections back to the LVDS output pins of the ADS528x that cause degraded signal integrity. By enabling an

internal termination (between the positive and negative outputs) for the LVDS buffers, the signal integrity can be

significantly improved in such scenarios. To set the internal termination mode, the EN_LVDS_TERM bit should

be set to '1'. Once this bit is set, the internal termination values for the bit clock, frame clock, and data buffers

can be independently programmed using sets of three bits. Table 6 shows an example of how the internal

termination of the LVDS buffer driving the bit clock is programmed (the method is similar for the frame clock and

data buffers). These termination values are only typical values and can vary by up to ±20% across temperature

and from device to device.

Table 6. Bit Clock Internal Termination

INTERNAL TERMINATION BETWEEN

TERM_LCLK<2> TERM_LCLK<1> TERM_LCLK<0> LCLK

AND LCLK

IN Ω

0 0 0 None

0 0 1 260

0 1 0 150

0 1 1 94

1 0 0 125

1 0 1 80

1 1 0 66

1 1 1 55