Maxim MAX12557 manual Output Codes vs. Input Voltage

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)

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