Datasheet
SYSCLK
0.8 V
2.0 V
t
CLKIL
t
CLKIH
T0005-03
RESET AND POWER DOWN
1024 System Clock Periods
Reset Reset Removal
4.4 V
4.0 V
3.6 V
V
CC
/ V
DD
Internal Reset
System Clock
T0014-01
3 Clocks Minimum
PCM1800
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............................................................................................................................................... SBAS071B – OCTOBER 2000 – REVISED AUGUST 2008
Table 1. System Clock Frequencies
SAMPLING RATE FREQUENCY SYSTEM CLOCK FREQUENCY (MHz)
(kHz)
256 f
s
384 f
s
512 f
s
32 8.1920 12.2880 16.3840
44.1 11.2896 16.9344 22.5792
48 12.2880 18.4320 24.5760
System clock pulse duration, HIGH t
(CLKIH)
12 ns (min)
System clock pulse duration, LOW t
(CLKIL)
12 ns (min)
Figure 19. System Clock Timing
The PCM1800 has both an internal power-on reset circuit and an external forced reset (RSTB, pin 6). The
internal power-on reset initializes (resets) when the supply voltage (V
CC
/V
DD
) exceeds 4 V (typical). To initiate the
reset sequence externally, apply a logic-level LOW to the RSTB pin.
The RSTB pin is terminated by an internal pulldown resistor. If the RSTB pin is unconnected, the ADC remains in
the reset state. Because the system clock is used as the clock signal for the reset circuit, the system clock must
be supplied as soon as power is applied; more specifically, the device must receive at least three system clock
cycles before V
DD
> 4 V and RSTB = HIGH. If this system clock requirement cannot be assured in an application,
RSTB must be held LOW until the system clock is supplied. While V
CC
/V
DD
< 4 V (typical), RSTB = LOW, and for
1024 system clock periods after V
CC
/V
DD
> 4.0 V and RSTB = HIGH, the PCM1800 stays in the reset state and
the digital output is forced to zero. The digital output is valid 18,436 f
S
periods after release from the reset state.
During reset, the logic circuits and the digital filter stop operating and enter the power-down mode. Figure 20 and
Figure 21 illustrate the internal power-on reset and external reset timing.
Figure 20. Internal Power-On Reset Timing
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