LTC2215CUP datasheet(28/36 Pages) LINER

28 / 36 page

LTC2216/LTC2215

22165f

Overﬂow Bit

An overﬂow output bit (OF) indicates when the converter

is over-ranged or under-ranged. In CMOS mode, a logic

high on the OFA pin indicates an overﬂow or underﬂow on

the A data bus, while a logic high on the OFB pin indicates

an overﬂow on the B data bus. In LVDS mode, a differen-

tial logic high on OF+/OF– pins indicates an overﬂow or

underﬂow.

Output Clock

The ADC has a delayed version of the encode input avail-

able as a digital output, CLKOUT. The CLKOUT pin can

be used to synchronize the converter data to the digital

system. This is necessary when using a sinusoidal en-

code. In both CMOS modes, A bus data will be updated

as CLKOUTA falls and CLKOUTB rises. In demultiplexed

CMOS mode the B bus data will be updated as CLKOUTA

falls and CLKOUTB rises.

In Full Rate CMOS Mode, only the A data bus is active;

data may be latched on the rising edge of CLKOUTA or

the falling edge of CLKOUTB.

In demultiplexed CMOS mode CLKOUTA and CLKOUTB

will toggle at 1/2 the frequency of the encode signal. Both

the A bus and the B bus may be latched on the rising edge

of CLKOUTA or the falling edge of CLKOUTB.

Digital Output Randomizer

Interference from the ADC digital outputs is sometimes

unavoidable. Interference from the digital outputs may be

from capacitive or inductive coupling, or coupling through

the ground plane. Even a tiny coupling factor can result in

discernible unwanted tones in the ADC output spectrum.

By randomizing the digital output before it is transmitted

off chip, these unwanted tones can be randomized, trading

a slight increase in the noise ﬂoor for a large reduction in

unwanted tone amplitude.

The digital output is “Randomized” by applying an exclu-

sive-OR logic operation between the LSB and all other data

output bits. To decode, the reverse operation is applied;

that is, an exclusive-OR operation is applied between the

LSB and all other bits. The LSB, OF and CLKOUT output

are not affected. The output Randomizer function is active

when the RAND pin is high.

Output Driver Power

Separate output power and ground pins allow the output

drivers to be isolated from the analog circuitry. The power

supply for the digital output buffers, OVDD, should be tied

to the same power supply as for the logic being driven.

For example, if the converter is driving a DSP powered

by a 1.8V supply, then OVDD should be tied to that same

1.8V supply. In CMOS mode OVDD can be powered with

any logic voltage up to the 3.6V. OGND can be powered

with any voltage from ground up to 1V and must be less

than OVDD. The logic outputs will swing between OGND

and OVDD. In LVDS Mode, OVDD should be connected to

a 3.3V supply and OGND should be connected to GND.

Figure 14. Functional Equivalent of Digital Output Randomizer

•

CLKOUT

D15 D0

D14 D0

D2 D0

D1 D0

RAND = HIGH,

SCRAMBLE

ENABLED

D14

D15

CLKOUT

RAND

22165 F14

LTC2216/LTC2215

APPLICATIONS INFORMATION

LTC2215CUP Datasheet(PDF) 28 Page - Linear Technology

LTC2215CUP Datasheet(HTML) 28 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Datasheet Download

Link URL