AT85C51SND3Bx
Schematic
Figure 6. Regulator Connection
HVDD
RLVDD
VSS
(
)
CHV
CLV *
VSS
Note:
Depending on power supply scheme, CLV may replace CDC capacitor (see Figure 8).
Low Voltage DC-DC in
AT85C51SND3B3
The low voltage output DC-DC converter supplies power to the internal device and
external devices through LVDD power pin. It operates from a single AAA battery. Its
nominal voltage output is 1.8V.
DC-DC Start-Up
DC-DC start-up is done by asserting the DCPWR input until the voltage reaches its
nominal value (see Section “Power Fail Detector”) and firmware starts execution and
sets the DCEN bit in PCON to maintain the DC-DC enabled. DCPWR input can then be
released. As shown in Figure 8 DCPWR input is asserted by pressing a key connected
to BVSS.
Figure 7. DC-DC Start-Up Phase
DCPWR
LVDD
DCEN
Firmware
Start-Up
DC-DC
Off
DC-DC
Start-Up
DC-DC
On
DC-DC Shut-Down
DC-DC Connection
DC-DC shut-down is done by two different ways:
•
•
Clearing the DCEN bit while DCPWR pin is de-asserted
Detecting the presence of an internal or external 3V supply, e.g. when the device is
connected to USB, DC-DC is disabled to save battery power(1).
Note:
1. If DCEN bit is left set, the DC-DC will restart as soon as the USB power supply
disappears.
Figure 8 shows how to connect external components, inductance and components
value along with power characteristics are specified in the section “DC characteristics”.
Figure 8. Battery DC-DC Connection
BVDD
RLVDD
LDC
LVDD
( )
DCLI
CDC1
*
CDC2
VSS
BVSS
CVSS
DCPWR
Note:
Depending on power supply scheme, CDC1 may replace CLV capacitor (see Figure 6).
19
7632A–MP3–03/06
ATMEL [ ATMEL ]
