RabbitCore eDisplay OP7200, Руководство пользователя

Страница: 149 / 174

User’s Manual 143
B.2.3 Battery-Backup Circuit
Figure B-3 shows the battery-backup circuit located on the OP7200’s RabbitCore module.
Figure B-3. OP7200 Backup Battery Circuit
The battery-backup circuit serves three purposes:
•
It reduces the battery voltage to the SRAM and to the real-time clock, thereby limiting
the current consumed by the real-time clock and lengthening the battery life.
•
It ensures that current can flow only out of the battery to prevent charging the battery.
•
A voltage, VOSC, is supplied to U6, which keeps the 32.768 kHz oscillator working
when the voltage begins to drop.
VRAM and Vcc are nearly equal (<100 mV, typically 10 mV) when power is supplied to
the OP7200.
R38
10 k W
VRAM
VBAT
R41
11 k W
2 k W
R39
VBAT
Vcc
22 k W
R37
47 k W
VOSC
R36
D1
D3
D2
C17
10 nF
C27
10 nF