u-blox LISA-C2 Series, Руководство по системной интеграции

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LISA-C2 series and FW75-C200 - System Integration Manual
UBX-13000620 - R21 Early Production Information System description
Page 19 of 103
1.6 System functions
1.6.1 Module power-on
The module power-on sequence is initiated in one of these two ways:
•
Rising edge on the
VCC
pin to a valid voltage for module supply
AND
if the
PWR_ON
pin is permanently
low when VCC is applied
•
Falling edge on the PWR_ON pin (hold pin low for >300 ms)
Name Description Remarks
PWR_ON Power-on input PWR_ON pin has internal pull up resistor. Recommended to
use open collector or drain configuration to pull down.
Table 9: Power-on pin
The PWR_ON pin ESD sensitivity rating is 1 kV (Human Body Model according to JESD22-A114F). Higher
protection level could be required if the line is externally accessible on the application board. Higher
protection level can be achieved by mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor
array) on the line connected to this pin.
1.6.1.1 Rising edge on VCC
When a supply is connected to VCC pins, the module supply supervision circuit controls the subsequent
activation of the power-up state: the module is switched on when the voltage rises up to the VCC operating
range minimum limit (3.4 V). (See LISA-C2 series Data Sheet [1] or the FW75-C200 Data Sheet [2]), provided that
the
PWR_ON
pin is permanently low when VCC is applied.
1.6.1.2 Falling edge on PWR_ON
The module power-on sequence starts when a falling edge is forced on the PWR_ON input pin. After applying a
falling edge, it is suggested to hold a low level on the PWR_ON signal for at least 300 ms to properly switch on
the module.
The electrical characteristics of the
PWR_ON
input pin are different from the other digital I/O interfaces: the high
and the low logic levels have different operating ranges. The detailed electrical characteristics are described in
the
LISA-C2 series Data Sheet
[1] or the
FW75-C200 Data Sheet
[2].
Once the module has been turned on,
PWR_ON pin has no effect. On the other hand it makes no sense to keep
this pin low once the module has been turned on: if the pin is kept low it will draw unnecessary current.
Following are some typical examples of application circuits to turn the module on using the
PWR_ON
input pin.
The simplest way to turn on the module is to use a push button that shorts the PWR_ON pin to ground.
If the
PWR_ON
input is connected to an external device (e.g. application processor), it is suggested to use an
open drain output on the external device.