AS1545
Datasheet - Application Information
To enter partial power-down mode, the conversion process must be interrupted by bringing CSN high anywhere after
the second falling edge of SCLK and before the 10th falling edge of SCLK, as shown in Figure 50. Once CSN is
brought high in this window of SCLKs, the part enters partial power-down, the conversion that was initiated by the
falling edge of CSN is terminated, and DOUTA and DOUTB go back into three-state. If CSN is brought high before the
second SCLK falling edge, the part remains in normal mode and does not power down. This avoids accidental power-
down due to glitches on the CSN line.
Figure 50. Partial Power-Down Mode
CSN
2
1
10
15
SCLK
DOUTA
DOUTB
THREE-STATE
To exit this mode of operation and power up the AS1545 again, a dummy conversion is performed. On the falling edge
of CSN, the device begins to power up and continues to power up as long as CSN is held low until after the falling edge
of the 10th SCLK. The device is fully powered up after approximately 1 µs has elapsed, and valid data results from the
next conversion, as shown in Figure 47. If CSN is brought high before the second falling edge of SCLK, the AS1545
again goes into partial power-down. This avoids accidental power-up due to glitches on the CSN line. Although the
device may begin to power up on the falling edge of CSN, it powers down again on the rising edge of CSN. If the
AS1545 is already in partial power-down mode and CSN is brought high between the second and 10th falling edges of
SCLK, the device enters full power-down mode.
Power-Up Times
As described in detail, the AS1545 has two power-down modes, partial power-down and full power-down. This section
deals with the power-up time required when coming out of either of these modes. It should be noted that the power-up
times, as explained in this section, apply with the recommended capacitors in place on the DCAPA and DCAPB pins.
The power-up time is always 1µs, independent of the mode currently in.
Note: It is important to note that, when using the internal reference, charging the external reference capacitance typ-
ically needs around 250µs but can take up to 1ms.
When power supplies are first applied to the AS1545, the ADC may power up in either of the power-down modes or
normal mode. Because of this, it is best to allow a dummy cycle to elapse to ensure the part is fully powered up before
attempting a valid conversion. Likewise, if it is intended to keep the part in the partial power-down mode immediately
after the supplies are applied, then two dummy cycles must be initiated. The first dummy cycle must hold CSN low until
after the 10th SCLK falling edge (see Figure 46); in the second cycle, CSN must be brought high before the 10th SCLK
edge but after the second SCLK falling edge (see Figure 50). Alternatively, if it is intended to place the part in full
power-down mode when the supplies are applied, then three dummy cycles must be initiated. The first dummy cycle
must hold CSN low until after the 10th SCLK falling edge (see Figure 46); the second and third dummy cycles place
the part in full power-down (see Figure 48).
Once supplies are applied to the AS1545, enough time must be allowed for any external reference to power up and
charge the various reference buffer decoupling capacitors to their final values.
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