Datasheet
27
9009101114fa
LTM9011-14/
LTM9010-14/LTM9009-14
applicaTions inForMaTion
Programmable LVDS Output Current
The default output driver current is 3.5mA. This current
can be adjusted by control register A2 in the serial pro-
gramming mode. Available current levels are 1.75mA,
2.1mA, 2.5mA, 3mA, 3.5mA, 4mA and 4.5mA. In the
parallel programming mode, the SCK pin can select either
3.5mA or 1.75mA.
Optional LVDS Driver Internal Termination
In most cases, using just an external 100Ω termina-
tion resistor will give excellent LVDS signal integrity. In
addition, an optional internal 100Ω termination resistor
can be enabled by serially programming mode con-
trol register A2. The internal termination helps absorb
any reflections caused by imperfect termination at the
receiver. When the internal termination is enabled, the
output driver current is doubled to maintain the same
output voltage swing. In the parallel programming
mode the SDO pin enables internal termination. Internal
termination should only be used with 1.75mA, 2.1mA or
2.5mA LVDS output current modes.
DATA FORMAT
Table 2 shows the relationship between the analog input
voltage and the digital data output bits. By default the
output data format is offset binary. The 2’s complement
format can be selected by serially programming mode
control register A1.
Digital Output Randomizer
Interference
from the A/D digital outputs is sometimes
unavoidable. Digital interference may be from capacitive or
inductive coupling or coupling through the ground plane.
Even a tiny coupling factor can cause unwanted tones
in the ADC output spectrum. By randomizing the digital
output before it is transmitted off chip, these unwanted
tones can be randomized which reduces the unwanted
tone amplitude.
The digital output is randomized by applying an exclusive-
OR logic operation between the LSB and all other data
output bits. To decode, the reverse operation is applied
—an exclusive-OR operation is applied between the
LSB and all other bits. The FR and DCO outputs are not
affected. The output randomizer is enabled by serially
programming mode control register A1.
Table 2. Output Codes vs Input Voltage
A
IN
+
– A
IN
–
(2V RANGE)
D13-D0
(OFFSET BINARY)
D13-D0
(2’s COMPLEMENT)
>1.000000V
+0.999878V
+0.999756V
11 1111 1111 1111
11 1111 1111 1111
11 1111 1111 1110
01 1111 1111 1111
01 1111 1111 1111
01 1111 1111 1110
+0.000122V
+0.000000V
–0.000122V
–0.000244V
10 0000 0000 0001
10 0000 0000 0000
01 1111 1111 1111
01 1111 1111 1110
00 0000 0000 0001
00 0000 0000 0000
11 1111 1111 1111
11 1111 1111 1110
–0.999878V
–1.000000V
<–1.000000V
00 0000 0000 0001
00 0000 0000 0000
00 0000 0000 0000
10 0000 0000 0001
10 0000 0000 0000
10 0000 0000 0000