PCM78 Burr-Brown Corporation, PCM78 Datasheet - Page 12

• Manufacturer Part Number: PCM78
• Description: 16-Bit Audio ANALOG-TO-DIGITAL CONVERTER
• Manufacturer: Burr-Brown Corporation

FIGURE 7. Conversion Timing when using External Clock.
if the convert clock rises before the S
condition is avoided as long as the frequency of S
is at least 1.5 times that of the conversion clock.
The internal convert command is generated upon S
Latch going low, and its falling edge occurs upon the first
falling edge of S
S
Clock to insure proper latching. In many applications, the
S
audio systems, typically known as WDCK. Figure 10
includes an example of this application.
FIGURE 8. Convert Command Timing Circuit for Use with External Clock.
OUT2
OUT2
PCM78 TIMING SPECIFICATIONS
T
NOTE: (1) The PCM78 does not contain dynamic digital circuitry, and can be clocked as slowly as the user wishes. In typical applications, the longest clock
period may be as long as 1 s.
Command
Clock Out
A
TIME
= +25 C, V
Convert
T
T
T
T
T
T
T
T
T
Status
S
Latch should remain low for at least 2 cycles of S
1
2
3
4
5
6
7
8
9
Latch can be the 2f
Clock
OUT 1
Data
Ext
(Convert)
Sample
EXTERNAL CLOCK pulse width
EXTERNAL CLOCK period
Delay from falling edge of EXTERNAL CLOCK to rising edge of CONVERT COMMAND
CONVERT COMMAND pulse width
Delay from falling edge of CONVERT COMMAND to rising edge of EXTERNAL CLOCK
Delay from falling edge of CONVERT COMMAND to rising edge of CLOCK OUT
Delay from rising edge of CLOCK OUT to rising edge of STATUS
Delay from rising edge of CLOCK OUT to bit data valid
Delay from rising edge of 17th clock pulse to falling edge of STATUS
DESCRIPTION
+5V
®
DD
PCM78
Clock
(Ext)
PCM78
= +5V, guaranteed by sample testing; these parameters are not 100% tested in production.
OUT2
T
1
D
T
2
C
Clock after S
T
T
Q
3
4
S
T
7
Q
signal present in many digital
T
Clock
6
1
T
5
D
C
Q
OUT2
T
Q
8
2
OUT2
Command
Latch goes low.
D
Convert
Clock. This
Q
OUT2
Q3
Clock
OUT2
OUT2
12
The data read out on S
previously performed, while the data that is present on
S
tion as it occurs.
SHORT CYCLE
The PCM78 has the ability to be short cycled to a resolution
less than 16 bits. This is accomplished by driving the Short
Cycle pin (pin 18) low when the conversion is to be
terminated, and holding it low until the next convert
command is given. The circuit in Figure 11 will accomplish
this function.
OUT1
Clock (Ext)
(Convert)
PCM78
Sample
Clock
is the real time readout of the successive approxima-
Q
Q
Q
1
2
3
MIN
140
–30
50
10
20
40
15
6
8
OUT2
is from the conversion
TIME (ns)
TYP
125
290
50
50
75
10
17
10
0
Command
Convert
T
9
MAX
420
200
430
460
30
20
30
(1)
(1)