Power-Up Time Acceleration

APPLICATION NOTE AND9311/D
POWER-UP
TIME ACCELERATION
Revision P1
2
Table of Contents
1. Overview..................................................................................................... 3
2. Power-up acceleration ................................................................................ 4
Implementation 1 .......................................................................................... 4
Implementation 2 .......................................................................................... 5
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3
Overview
1. Overview
AXSEM RF chip have typical start-up times from sleep to oscillator and references
running are in the order of 3ms1. This time can vary with temperature and be in rare
cases over 10ms. The start-up time is not specified and not controlled. For synchronous
applications this is not desirable. Therefore we are presenting two easy ways to reduce
and control the start-up time to a constant value.
This document applies to the devices AX5051, AX5151, AX5031, AX5131 and AX50424.
1
This value depends on the specific crystal used
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Power-up acceleration
2. Power-up acceleration
Implementation 1
Connect a digital output pin PIO directly from a micro-controller to the VREG pin of the
RF device. The default setting of PIO should be Hi-Z.
After powering up the RF device PIO has to be set from Hi-Z to 1 and back to Hi-Z. This
will induce a voltage kick to VREG and helps the device to power up in minimum time.
VDD_IO
Microcontroller
AXSEM
RF device
VDD
VREG
PIO
C=1uF
figure 1: Implementation 1
Powering up references and oscillators should now be done as follows 2:
1. Set PWRMODE to STANDBY (register value 0x05)
2. Set PIO to output 1
3. Wait at least 200s
4. Set PIO back to Hi-Z
2
Refer to the product specific Programming Manual for details on power up sequences,
see http://www.axsem.com
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Power-up acceleration
Implementation 2
This implementation uses a GPIO pin from the RF device itself, so no extra pin from a
micro-controller or any other external device is required.
Choose a GPIO pin (SYSCLK or IRQ) and connect it via a capacitor C 2 to the VREG pin.
The pin numbers of the GPIO pins that can be used for each of AXSEM's RF device are
shown in table 1.
VDD_IO
AXSEM
RF device
C1=1F
GPIO
VDD
VREG
C2=1F
figure 2: Implementation 2
Powering up references and oscillators should now be done as follows 3:
1. Set GPIO pin to output 0 (registers PINCFG1 and PINCFG2)
2. Set PWRMODE register to STANDBY (register value 0x05)
3. Set GPIO pin to output 1
4. Wait at least 30us
5. Set GPIO pin back to 0
Note, that C2 should be approximately the same size as C 1. If the capacitors are chosen
greater than 1F, the minimum wait time in step 3 will be longer.
3
Refer to the product specific Programming Manual for details on power up sequences
and GPIO pin configuration, see http://www.axsem.com
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6
Power-up acceleration
Device
IRQ
SYSCLK
AX5051
19
13
AX5151
20
14
AX5031
14
7
AX5131
16
10
AX50424
19
13
table 1: GPIO pin numbers
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