SPT7937 datasheet(9/11 Pages) CADEKA

9 / 11 page

3/5/02

SPT7937

Figure 6 – On-Chip Protection Circuit

VDD

Analog

Pad

120 W

INPUT PROTECTION

All I/O pads are protected with an on-chip protection circuit

shown in figure 6. This circuit provides ESD robustness to

3.5 kV and prevents latch-up under severe discharge con-

ditions without degrading analog transition times.

CLOCK INPUT

The SPT7937 is driven from a single-ended TTL-input

clock. Because the pipelined architecture operates on the

rising edge of the clock input, the device can operate over

a wide range of input clock duty cycles without degrading

the dynamic performance.

DIGITAL OUTPUTS

The digital outputs (D0–D12) are driven by a separate sup-

ply (OVDD) ranging from +3 V to +5 V. This feature makes it

possible to drive the SPT7937’s TTL/CMOS-compatible

outputs with the user’s logic system supply. The format of

the output data (D0–D11) is straight binary. (See table III.)

The outputs are latched on the rising edge of CLK.

Table III – Output Data Information

ANALOG INPUT

OUT OF RANGE

OUTPUT CODE

D12

D11–D0

+F.S. + 1/2 LSB

1111 1111 1111

+F.S. –1/2 LSB

1111 1111 111Ø

+1/2 F.S.

ØØØØ ØØØØ ØØØØ

+1/2 LSB

0000 0000

000Ø

0.0 V

0000 0000

0000

(Ø indicates the flickering bit between logic 0 and 1).

OUT-OF-RANGE OUTPUT

The Out-of-Range Output (D12) is an indication that the

analog input signal is outside the full-scale input voltage

range by 1 LSB. When this condition occurs, D12 will

switch to logic 1. All other data outputs (D0 to D11) will

remain at logic 0 or 1 as long as D12 remains at logic 1.

EVALUATION BOARD

The EB7937 evaluation board is available to aid designers

in demonstrating the full performance of the SPT7937.

This board includes a reference circuit, clock driver circuit,

output data latches and an on-board reconstruction of the

digital data. An application note (AN7937) describing the

operation of this board, as well as information on the test-

ing of the SPT7937, is also available. Contact the factory

for price and availability.

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