UMTS/HSPA Module Series
UG96 Hardware Design
UG96_Hardware_Design 36 / 76
The following figure shows the reference circuit for VRTC backup.
Large
Capacitance
Capacitor
Module
RTC
Core
1K
VRTC
C
Figure 19: RTC Supply from Capacitor
In order to evaluate the capacitance of capacitor according to the backup time, the following parameters
should be considered:
⚫
VRTC - The starting voltage of the capacitor. (Volt)
⚫
VRTC
MIN
- The minimum voltage acceptable for the RTC circuit. (Volt)
⚫
I - The current consumption of the RTC circuitry when VBAT=0. (Ampere)
⚫
B
Time
- Backup Time. (Second)
⚫
C - The backup capacitance. (Farad)
When the power is off and only VRTC is running, the way of calculating the backup capacitor is as follows:
C=B
Time
*I/ (VRTC-VRTC
MIN
)
For example, when the capacitor is 1000uF:
⚫
VRTC=1.8V
⚫
VRTC
MIN
=1.0V
⚫
I=2uA
⚫
C=1000uF
The backup time is about 400s.
3.10. UART Interface
The module provides 7-wire UART interface.
The UART interface supports 300bps, 1200bps, 2400bps, 4800bps, 9600bps, 19200bps, 38400bps,
57600bps, 115200bps, 230400bps, 460800bps and 921600bps baud rates, and the default is auto-baud
rate 4800bps~115200bps. This interface can be used for data transmission, AT command communication
and firmware upgrade.