Cirrus Logic CS5451A - Manual (Page 11)

CS5451A
DS635F4 11
shifting of the analog inputs. The CPD pin and capacitor
C1 provide the necessary analog supply current as
shown in Figure 5. The Schottky diodes D1 and D2 are
chosen for their low forward voltages and high-speed
capabilities. The capacitor C2 provides the required
charge storage and bypassing of the negative supply.
The CPD output signal provides the charge pump driver
signal. The frequency of the charge pump driver signal
is synchronous to XIN. The nominal average frequency
is 1 MHz. The level on the VA- pin is fed back internally
so that the CPD output will regulate the VA- level to -2/3
of VA+ level.
The value of capacitor C1 (see Figure 5) is dependent
on the XIN clock frequency. The 39 nF value for C1 was
selected for a XIN clock frequency equal to 4.096 MHz.
For more information about the operation of this type of
charge pump circuit, the reader can refer to Cirrus Log-
ic, Inc.’s application note AN152: Using the
CS5521/24/28, and CS5525/26 Charge Pump Drive for
External Loads.
AGND
BAT 85
D1
C1
39 nF
C2
CPD
VA-
BAT 85
1 µF
D2
Figure 5. Generating VA- with a Charge Pump