Specifications
Table Of Contents
- Contents
- Tables
- Figures
- 1 Introduction
- 2 Interface Characteristics
- 2.1 Application Interface
- 2.2 RF Antenna Interface
- 2.3 Sample Application
- 3 Operating Characteristics
- 3.1 Operating Modes
- 3.2 Power Up/Power Down Scenarios
- 3.3 Power Saving
- 3.4 Power Supply
- 3.5 Operating Temperatures
- 3.6 Electrostatic Discharge
- 3.7 Blocking against RF on Interface Lines
- 3.8 Reliability Characteristics
- 4 Mechanical Dimensions, Mounting and Packaging
- 5 Regulatory and Type Approval Information
- 6 Document Information
- 7 Appendix
Cinterion
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ELS81-US Hardware Interface Description
2.1 Application Interface
53
els81-us_hid_v01.004 2017-09-27
Confidential / Preliminary
Page 33 of 107
2.1.7 RTC Backup
The internal Real Time Clock of ELS81-US is supplied from a separate voltage regulator in the
power supply component which is also active when ELS81-US is in Power Down mode and
BATT+ is available. An alarm function is provided that allows to wake up ELS81-US without
logging on to the RF network.
In addition, you can use the VDDLP pad to backup the RTC from an external capacitor. The
capacitor is charged from the internal LDO of ELS81-US. If the voltage supply at BATT+ is dis-
connected the RTC can be powered by the capacitor. The size of the capacitor determines the
duration of buffering when no voltage is applied to ELS81-US, i.e. the greater the capacitor the
longer ELS81-US will save the date and time. The RTC can also be supplied from an external
battery (rechargeable or non-chargeable). In this case the electrical specification of the VDDLP
pad (see Section 2.1.2) has to be taken in to account.
Figure 12 shows an RTC backup configuration. A serial 1k
resistor has to be placed on the
application next to VDDLP. It limits the input current of an empty capacitor or battery.
Figure 12: RTC supply variants
Capacitor
VDDLP
Processor and power
management
LRTC
RTC
Application interface
BATT+
Module
1k
GND