Cirrus Logic CS5372A - Manual (Page 24)

CS5371A CS5372A
24 DS748F3
8.4 SCR Latch-up Considerations
It is recommended to connect the VA- power
supply to system ground (GND) with a re-
verse-biased Schottky diode. At power up, if
the VA+ power supply ramps up before the
VA- supply is established, the VA- pin voltage
could be pulled above ground potential
through the CS5371A and CS5372A device. If
the VA- supply is pulled 0.7 V or more above
GND, SCR latch-up can occur. A reverse-bi-
ased Schottky diode will clamp the VA- voltage
a maximum of 0.3 V above ground to ensure
SCR latch-up does not occur at power up.
8.5 DC-DC Converters
Many low-frequency measurement systems
are battery powered and utilize DC-DC con-
verters to efficiently generate power supply
voltages. To minimize interference effects, op-
erate the DC-DC converter at a frequency
which is rejected by the digital filter, or operate
it synchronous to the MCLK rate.
A synchronous DC-DC converter whose oper-
ating frequency is derived from MCLK will the-
oretically minimize the potential for “beat
frequencies” to appear in the
measurement
bandwidth. However this requires the source
clock to remain jitter free within the DC-DC
converter circuitry. If clock jitter can occur with-
in the DC-DC converter (as in a PLL-based ar-
chitecture), it’s better to use a non-
synchronous DC-DC converter whose switch-
ing frequency is rejected by the digital filter.
During PCB layout, do not place high-current
DC-DC converters near sensitive analog com-
ponents. Carefully routing a separate DC-DC
“star” ground will help isolate noisy switching
currents away from the sensitive analog com-
ponents.