CS5471
and bypassing of the negative supply. The CPD 12.5%. Therefore, the value of C1 should be re-
output signal provides the charge pump driver sig- duced by 12.5%, making the new value for C1 to be
nal. The frequency of the charge pump driver sig-
nal is synchronous to XIN. The nominal average
frequency is 1 Mhz. The level on the VA- pin is fed
35 nF. For more information about the operation of
this type of charge pump circuit, the reader can re-
fer to Cirrus Logic, Inc.’s application note AN152:
back internally so that the CPD output will regulate Using the CS5521/24/28, and CS5525/26 Charge
the VA- level to -2/3 of VA+ level. Pump Drive for External Loads.
2.9 PCB Layout
For optimal performance, the CS5460A should be
placed entirely over an analog ground plane with
both the VA- and DGND pins of the device con-
nected to the analog plane. Place the analog-digital
plane split immediately adjacent to the digital por-
tion of the chip.
CPD
AGND
40 nF
C1
VA-
D2
BAT 85
BAT 85
D1
C2
1 µF
Note: Refer to the CDB5460A Evaluation Board for
suggested layout details and Applications Note
18 for more detailed layout guidelines. Before
layout, please call for our Free Schematic
Review Service.
Figure 5. Generating VA- with a Charge Pump
Note the value of C1 in Figure 5. The 40 nF value
is recommended when the input frequency present-
ed to the XIN pin is 4.00 MHz. If the user decides
to use an XIN frequency that is significantly differ-
ent than 4.00 MHz (if the XIN frequency is in-
creased/decreased by more than 5% of 4.00 MHz,
then it is recommended that the user should alter
the value of C1. The percentage change in the value
of C1 (with respect to a reference value of 40 nF)
should be inversely proportional to the percentage
change in the XIN frequency. For example, if the
XIN frequency is increased from 4.00 MHz to 4.5
MHz, this represents a percentage increase of
10
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