Figure 2 – Timing Diagram 1
t
C
t
CLK
2
Clock
Reset
1
t
d
3
t
Set
Data
Valid (DAV)
Data
Output
(Channel A)
Data
Output
(Channel B)
t
OD
t
Hold
Invalid
4
Invalid
Invalid
t
OD
Invalid
Invalid
Invalid
Notes:
1) Data Valid is forced low on Reset = High.
2) Data updated on first rising edge of clock after Reset goes low.
3) Data Valid rising edge will occur on the second rising edge of Clock
after Reset goes low. Use the rising edge of Data Valid to latch the ADC output data.
4) Analog Input Data is sampled during the first clock cycle after Reset goes low.
Valid data output from this sample will be available 12 clock cycles
later (6 Data Valid cycles). All data during the 12 clock cycle latency is invalid.
CLOCK INPUT
The SPT7852 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.
The device's sample rate is 1/2 of
the input clock frequency. (See timing diagram.)
The reset pin is low for normal device operation. When reset
is brought high, Data Valid (DAV) is immediately forced low
and data output updates are suspended. Operation will re-
sume on the first rising edge of the clock after the reset pin
has been brought low. The first Data Valid rising edge will
occur on the second edge of the clock after the reset goes
low.
The first analog input sample will be taken during the first
clock cycle after reset goes low. Valid data from this
sample will be available 12 clock cycles later. All data dur-
ing this 12 cycle latency will be invalid (Refer to figure 3,
Timing Diagram 2.)
TIMING AND RESET FUNCTION
The two on-board ADCs in the SPT7852 are driven off of a
single external TTL clock. This external clock must be 2X
the desired sample rate. In applications that require a
known phase relationship between the clock, analog input
sampling and valid data output, a reset function is provided
to establish a known phase relationship. (Because of the 2X
clock, an exact phase relationship will not be known other-
wise.) Refer to figure 2, Timing Diagram 1.
SPT7852
6
1/12/00
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
