REF_P

Dual, 65Msps, 14-Bit, IF/Baseband ADC

externally isolates it from heavy capacitive loads. Refer to the MAX12557 EV kit schematic for recommendations of how to drive the DAV signal through an external buffer.

Data Out-of-Range Indicator The DORA and DORB digital outputs indicate when the analog input voltage is out of range. When DOR_ is high, the analog input is out of range. When DOR_ is low, the analog input is within range. The valid differential input range is from (VREF_P - VREF_N) x 2/3 to (VREF_N -

V ) x 2/3. Signals outside of this valid differential range cause DOR_ to assert high as shown in Table 1.

DOR is synchronized with DAV and transitions along with the output data D13–D0. There is an 8 clock-cycle latency in the DOR function as is with the output data (Figure 5). DOR_ is high impedance when the MAX12557 is in power-down (PD = high). DOR_ enters a high-impedance state within 10ns after the rising edge of PD and becomes active 10ns after PD’s falling edge.

Digital Output Data and Output Format Selection The MAX12557 provides two 14-bit, parallel, tri-state output buses. D0A/B–D13A/B and DORA/B update on

the falling edge of DAV and are valid on the rising edge of DAV.

The MAX12557 output data format is either Gray code or two’s complement depending on the logic input G/T. With G/T high, the output data format is Gray code. With G/T low, the output data format is set to two’s com- plement. See Figure 8 for a binary-to-Gray and Gray-to- binary code conversion example.

The following equations, Table 3, Figure 6, and Figure 7 define the relationship between the digital output and the analog input.

Gray Code (G/T = 1):

VIN_P - VIN_N = 2/3 x (VREF_P - VREF_N) x 2 x

(CODE10 - 8192) / 16,384

Two’s Complement (G/T = 0):

VIN_P - VIN_N = 2/3 x (VREF_P - VREF_N) x 2 x CODE10 / 16,384

where CODE10 is the decimal equivalent of the digital output code as shown in Table 3.

MAX12557

Table 3. Output Codes vs. Input Voltage

GRAY-CODE OUTPUT CODE

TWO’S-COMPLEMENT OUTPUT CODE

 

 

(G/T = 1)

 

 

 

 

(G/T = 0)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HEXADECIMAL

 

DECIMAL

 

 

 

HEXADECIMAL

DECIMAL

VIN_P - VIN_N

 

 

 

 

EQUIVALENT

 

 

 

EQUIVALENT

BINARY

 

 

EQUIVALENT

 

BINARY

 

 

EQUIVALENT

VREF_P = 2.418V

D13A–D0A

DOR

OF

 

OF

D13A–D0A

 

DOR

OF

OF

VREF_N = 0.882V

 

D13A–D0A

 

D13A–D0A

D13B–D0B

 

 

D13A–D0A

 

D13B–D0B

 

 

D13A–D0A

 

 

 

 

D13B–D0B

 

 

D13B–D0B

 

 

 

 

D13B–D0B

 

 

 

 

D13B–D0B

 

 

 

 

 

(CODE10)

 

 

 

(CODE10)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

>+1.023875V

10 0000 0000 0000

1

 

0x2000

+16,383

01 1111 1111 1111

1

0x1FFF

+8191

(DATA OUT OF

 

 

 

 

 

 

 

 

 

 

 

RANGE)

 

 

 

 

 

 

 

 

 

 

 

 

10 0000 0000 0000

0

 

0x2000

+16,383

01 1111 1111 1111

0

0x1FFF

+8191

+1.023875V

 

 

 

 

 

 

 

 

 

 

 

 

10 0000 0000 0001

0

 

0x2001

+16,382

01 1111 1111 1110

0

0x1FFE

+8190

+1.023750V

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

11 0000 0000 0011

0

 

0x3003

+8194

00 0000 0000 0010

0

0x0002

+2

+0.000250V

 

 

 

 

 

 

 

 

 

 

11 0000 0000 0001

0

 

0x3001

+8193

00 0000 0000 0001

0

0x0001

+1

+0.000125V

 

 

 

 

 

 

 

 

 

 

11 0000 0000 0000

0

 

0x3000

+8192

00 0000 0000 0000

0

0x0000

0

+0.000000V

01 0000 0000 0000

0

 

0x1000

+8191

11 1111 1111 1111

0

0x3FFF

-1

-0.000125V

 

 

 

 

 

 

 

 

 

 

01 0000 0000 0001

0

 

0x1001

+8190

11 1111 1111 1110

0

0x3FFE

-2

-0.000250V

 

 

 

 

 

 

 

 

 

 

 

 

00 0000 0000 0001

0

 

0x0001

+1

10 0000 0000 0001

0

0x2001

-8191

-1.023875V

 

 

 

 

 

 

 

 

 

 

00 0000 0000 0000

0

 

0x0000

0

10 0000 0000 0000

0

0x2000

-8192

-1.024000V

 

 

 

 

 

 

 

 

 

 

 

<-1.024000V

00 0000 0000 0000

1

 

0x0000

 

0

10 0000 0000 0000

 

1

0x2000

-8192

(DATA OUT OF

 

 

 

 

 

 

 

 

 

 

 

RANGE)

 

 

 

 

 

 

 

 

 

 

 

 

______________________________________________________________________________________ 19

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Maxim MAX12557 manual Output Codes vs. Input Voltage