Sony Ericsson Automatic power on circuit, GM47, GM48, GR47, GR48 Application Note

Application Note

Automatic power on circuit for

GM/GR 47/48

First edition (March 2004)

Sony Ericsson Mobile Communications publishes this manual without making any warranty as to the

content contained herein. Further Sony Ericsson Mobile Communications reserves the right to make
modifications, additions and deletions to this manual due to typographical errors, inaccurate information,
or improvements to programs and/or equipment at any time and without notice. Such changes will,
nevertheless be incorporated into new editions of this manual.

All rights reserved.

© Sony Ericsson Mobile Communications, 2004

Automatic power on circuit for GM/GR 47/48

Contents

INTRODUCTION ................................................................................................................. 4

1

2 SONY ERICSSON MODULE ACTIVATION CIRCUIT PROPOSAL ................................... 5

2.1 DETAILED DESCRIPTION OF THE ACTIVATION SEQUENCE ................................................... 5

APPENDIX ................................................................................................................................. 6

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Automatic power on circuit for GM/GR 47/48

1 Introduction

This Application Note describes a method by which the GR47 GSM/GPRS
Module may be activated automatically when power is applied.

The solution requires external circuitry for monitoring the supply voltage
and generating a pulse on the GR47 ON/OFF signal line.

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Automatic power on circuit for GM/GR 47/48

2 Sony Ericsson Module Activation Circuit Proposal

The Sony Ericsson proposal for ensuring that the module automatically
switches on when power is applied is detailed here. The description refers
to circuitry presented in the schematic of Figure 1 in the Appendix.

The circuit uses a MAX6804 supervisory circuit to detect when the power
applied to the GR47 reaches an acceptable level.

A 74HC123A one-shot circuit presents a pulse to the ON/OFF signal
connection of the GR47. The pulse is designed to exceed 0.5 seconds in
accordance with the GR47 design specification to activate the module.

Note: If the one-shot pulse is designed to be greater than 0.5 seconds but
less than 1.0 second, it may provide an ‘ON’ signal but not an ‘OFF’
signal.

Feedback of activated GR47 signals is used to disable the one-shot when
operation is normal. If the GR47 is turned off, this feedback mechanism
retriggers the one-shot and will automatically activate the module again. A
full datasheet for the 74HC123A can be downloaded from
www.fairchildsemi.com.

2.1 Detailed Description of the Activation Sequence

When power is applied to VCC, the MAX6804 holds ‘CLR’ low to allow ‘A’
and ‘B’ to stabilise and ‘Q’ stays low. When VCC reaches 3.3V, ‘RST’
goes high triggering the one-shot. ‘Q’ goes high and pulls ON/OFF low.
This activates the module and changes the state of ‘A’ disabling further
one-shot pulses. The one-shot pulse lasts for RC seconds.

When the one-shot pulse ends, the module should have stayed on. ‘CLR’
is high, ‘Q’ is low, ‘A’ is high and ‘B’ is low (both held by VIO output from
module).

If the module switches off, the VIO output from the module will deactivate
and turn ‘A’ low and ‘B’ high, one of which will re-trigger the one-shot. The
module will be turned back on again.

Note : It may be necessary to delay the OFF to ON transition time with a
small RC delay on the ‘A’ and ‘B’ inputs.

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Automatic power on circuit for GM/GR 47/48

Appendix

Figure 1 - One-Shot Switch-on Proposal Schematic

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