User's Guide

LM940 HW Design Guide
1VV0301352 Rev. 2 Page 6 of 68 2017-07-19
4. POWER SUPPLY ........................................................................ 26
Power Supply Requirements ........................................................ 26
Power Consumption ..................................................................... 26
General Design Rules .................................................................. 27
4.3.1. Electrical Design Guidelines ......................................................... 27
4.3.1.1. + 5V Input Source Power Supply – Design Guidelines ................ 27
4.3.2. Thermal Design Guidelines .......................................................... 27
4.3.3. Power Supply PCB layout Guidelines .......................................... 28
RTC .............................................................................................. 29
Reference Voltage ........................................................................ 29
Internal LDO for GNSS bias ......................................................... 30
5. ELECTRICAL SPECIFICATIONS ................................................ 31
Absolute Maximum Ratings – Not Operational ............................. 31
Recommended Operating Conditions .......................................... 31
6. DIGITAL SECTION ...................................................................... 32
Logic Levels ................................................................................. 32
6.1.1. 1.8V Pins – Absolute Maximum Ratings ...................................... 32
6.1.2. 1.8V Standard GPIOs ................................................................... 32
6.1.3. 1.8V SIM Card Pins ...................................................................... 33
6.1.4. 2.85V Pins – Absolute Maximum Ratings .................................... 33
6.1.5. SIM Card Pins @2.85V ................................................................ 33
Power On ..................................................................................... 34
6.2.1. Initialization and Activation State .................................................. 34
Power Off ..................................................................................... 35
Unconditional Hardware Reset ..................................................... 36
Communication ports ................................................................... 37
6.5.1. USB Interface ............................................................................... 37
6.5.2. SIM Interface ................................................................................ 39
6.5.2.1. SIM Schematic Example .............................................................. 40
6.5.3. Control Signals ............................................................................. 41
6.5.3.1. W_DISABLE_N ............................................................................ 41
6.5.3.2. WAKE_N ...................................................................................... 41
6.5.3.3. WAN_LED_N ............................................................................... 42
6.5.4. General Purpose I/O .................................................................... 42
6.5.4.1. Using a GPIO Pin as Input ........................................................... 43
6.5.4.2. Using a GPIO Pin as Output ........................................................ 43
6.5.5. I2C – Inter-integrated circuit ......................................................... 43