Rainbow-electronics MAX1127 Manual de usuario descargar pdf (Pagina 21)

MAX1127

Quad, 12-Bit, 65Msps, 1.8V ADC with

Serial LVDS Outputs

______________________________________________________________________________________ 21

Double Termination (DT)

As shown in Figure 8, the MAX1127 offers an optional,

internal 100Ω termination between the differential output

pairs (OUT_P and OUT_N, CLKOUTP and CLKOUTN,

FRAMEP and FRAMEN). In addition to the termination

at the end of the line, a second termination directly at

the outputs helps eliminate unwanted reflections down

the line. This feature is useful in applications where

trace lengths are long (>5in) or with mismatched

impedance. Drive DT high to select double termination,

or drive DT low to disconnect the internal termination

resistor (single termination). Selecting double termina-

tion increases the OV

supply current (see the

Electrical Characteristics table).

Power-Down Modes

The MAX1127 offers two types of power-down inputs,

PD0–PD3 and PDALL. The power-down modes allow

the MAX1127 to use power efficiently by transitioning to

a low-power state when conversions are not required.

Independent Channel Power-Down (PD0–PD3)

PD0–PD3 control the power-down mode of each chan-

nel independently. Drive a power-down input high to

power down its corresponding input channel. For exam-

ple, to power down channel 1, drive PD1 high. Drive a

power-down input low to place the corresponding input

channel in normal operation. The differential output

impedance of a powered-down output channel is

approximately 378Ω, when DT is low. The output imped-

ance of OUT_P, with respect to OUT_N, is 100Ω when

DT is high. See the Electrical Characteristics table for

typical supply currents with powered-down channels.

The state of the internal reference is independent of the

PD0–PD3 inputs. To power down the internal reference

circuitry, drive PDALL high (see the Global Power-

Down (PDALL) section).

DIFFERENTIAL INPUT VOLTAGE (LSB)

-2045 +2047+2045-1 0 +1-2047

0x800

0x801

0x802

0x803

0x7FF

0x7FE

0x7FD

0xFFF

0x000

0x001

FSR FSR

1 LSB =

2 x FSR

4096

FSR = 700mV x

REFIO

1.24V

TWO'S COMPLEMENT OUTPUT CODE (LSB)

Figure 6. Bipolar Transfer Function with Two’s Complement

Output Code (

/B = 0)

DIFFERENTIAL INPUT VOLTAGE (LSB)

-2045 +2047+2045-1 0 +1-2047

0x000

0x800

0x002

0x003

0xFFF

0xFFE

0xFFD

0x7FF

0x800

0x801

FSR FSR

1 LSB =

2 x FSR

4096

FSR = 700mV x

REFIO

1.24V

OFFSET BINARY OUTPUT CODE (LSB)

Figure 7. Bipolar Transfer Function with Offset Binary Output

Code (

/B = 1)

MAX1127

100Ω 100Ω

OUT_P/

CLKOUTP/

FRAMEP

OUT_N/

CLKOUTN/

FRAMEN

SWITCHES ARE CLOSED WHEN DT IS HIGH.

SWITCHES ARE OPEN WHEN DT IS LOW.

= 50Ω

Figure 8. Double Termination

1 2 ... 16 17 18 19 20 21 22 23 24 25

Serial LVDS Outputs 1

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Rainbow-electronics MAX1127 Manual de usuario Pagina 21

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