MAX12557 Datasheet, PDF (19/28 Pages) Maxim Integrated Products – Dual, 65Msps, 14-Bit, IF/Baseband ADC

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 (V_{REF_P} - V_{REF_N}) x 2/3 to (V_{REF_N} -
V_{REF_P}) 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):
V_{IN_P} - V_{IN_N} = 2/3 x (V_{REF_P} - V_{REF_N}) x 2 x
(CODE₁₀ - 8192) / 16,384
Two’s Complement (G/T = 0):
V_{IN_P} - V_{IN_N} = 2/3 x (V_{REF_P} - V_{REF_N}) x 2 x
CODE₁₀ / 16,384
where CODE₁₀ is the decimal equivalent of the digital
output code as shown in Table 3.
Table 3. Output Codes vs. Input Voltage
GRAY-CODE OUTPUT CODE
(G/T = 1)
TWO’S-COMPLEMENT OUTPUT CODE
(G/T = 0)
BINARY
D13A–D0A
D13B–D0B
HEXADECIMAL
EQUIVALENT
DECIMAL
EQUIVALENT
DOR
OF
D13A–D0A
OF
D13A–D0A
D13B–D0B
D13B–D0B
(CODE₁₀)
BINARY
D13A–D0A
D13B–D0B
DECIMAL
HEXADECIMAL
EQUIVALENT
EQUIVALENT
OF
DOR
OF
D13A–D0A
D13A–D0A
D13B–D0B
D13B–D0B
(CODE₁₀)
10 0000 0000 0000 1
0x2000
+16,383 01 1111 1111 1111 1
0x1FFF
+8191
10 0000 0000 0000 0
10 0000 0000 0001 0
0x2000
0x2001
+16,383
+16,382
01 1111 1111 1111 0
01 1111 1111 1110 0
0x1FFF
0x1FFE
+8191
+8190
V_{IN_P} - V_{IN_N}
V_{REF_P} = 2.418V
V_{REF_N} = 0.882V
>+1.023875V
(DATA OUT OF
RANGE)
+1.023875V
+1.023750V
11 0000 0000 0011 0
11 0000 0000 0001 0
11 0000 0000 0000 0
01 0000 0000 0000 0
01 0000 0000 0001 0
0x3003
0x3001
0x3000
0x1000
0x1001
+8194
+8193
+8192
+8191
+8190
00 0000 0000 0010 0
00 0000 0000 0001 0
00 0000 0000 0000 0
11 1111 1111 1111 0
11 1111 1111 1110 0
0x0002
0x0001
0x0000
0x3FFF
0x3FFE
+2
+0.000250V
+1
+0.000125V
0
+0.000000V
-1
-0.000125V
-2
-0.000250V
00 0000 0000 0001 0
00 0000 0000 0000 0
00 0000 0000 0000 1
0x0001
0x0000
0x0000
+1
10 0000 0000 0001 0
0x2001
0
10 0000 0000 0000 0
0x2000
0
10 0000 0000 0000 1
0x2000
-8191
-8192
-8192
-1.023875V
-1.024000V
<-1.024000V
(DATA OUT OF
RANGE)
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