2.5.2. DC/DC Converter
The DC/DC converter of the MAS 3504D is used to
generate a fixed power supply voltage even if the chip
is powered by battery cells in portable applications.
The DC/DC converter is designed for the application of
1 or 2 batteries or NiCd cells. The DC/DC converter is
switched on by activating the DCEN pin. Its output
power is sufficient for other ICs as well.
A 22
µ
H inductor is required for the application. The
important specification item is the inductor saturation
current rating, which should be greater than 2.5 times
the DC load current. The DC resistance of the inductor
is important for efficiency. The primary criterion for
selecting the output filter capacitor is low equivalent
series resistance (ESR), as the product of the inductor
current variation and the ESR determines the high-fre-
quency amplitude seen on the output voltage. The
Schottky diode should have a low voltage drop V
D
for
a high overall efficiency of the DC/DC converter. The
current rating of the diode should also be greater than
2.5 times the DC output current. The VSENS pin is
always connected to the output voltage at the low ESR
capacitor.
2.5.3. Stand-by Functions
The digital part of the MAS 3504D and the DC/DC con-
verter are turned on by setting WSEN. If only the DC/
DC converter should work, it can remain active byset-
ting DCEN alone to supply other parts of the applica-
tion even if the audio decoding part of the MAS 3504D
is not being used. The WSEN power-up pin of the digi-
tal part should be handled by the controller.
Please pay attention to the fact, that the I
2
C interface
is working only if the processor is powered up
(WSEN = 1).
CLKI
VDD
Start-up
oscillator
Start-up
divider
64...94
x2
AVDD
DCSO
DCSG
DC/DC
converter
optional
filter
22
µH
+
−
C
OUT
330
µF
Low ESR
+
32...47
+32
DCEN
voltage
monitor
PUP
WSEN
16
Power-On
Push Button
V
IN
≥
0.9 V
C
IN
330
µF
−
DCCF
8e
hex
9 10
0...15
10 kΩ
VSENSE
VSS
AVSS
47 kΩ
10 nF
47 kΩ
µ
Controller
Fig. 2–1:
DC/DC converter connections
Micronas
7
MICRONAS [ MICRONAS ]
