saa1575hl NXP Semiconductors, saa1575hl Datasheet - Page 22

• Manufacturer Part Number: saa1575hl
• Description: Global Positioning System Gps Baseband Processor
• Manufacturer: NXP Semiconductors

Philips Semiconductors
7.8.2.2
The ultimate use of the power control signals is up to the
user. However, two possibilities are presented as design
examples. The first example will operate correctly in
circuits where the rise times of the power supplies is slow
compared to any delay between the supplies to the
peripheral and core power domains.
In this example, both the PWRDN and PWRFAIL logic
inputs to the SAA1575HL are derived by comparing the
V
In general, since it is a lower voltage, the V
may hold and reach it’s nominal voltage quicker than the
V
As V
is taken LOW. This triggers an interrupt in the firmware
which is used to perform any required housekeeping. It is
assumed that there is time for this to be completed before
complete supply failure.
1999 Jun 04
handbook, full pagewidth
CC(P)
CC(P)
Global Positioning System (GPS)
baseband processor
CC(P)
V CC(P)
V CC(core)
PWRDN
PWRFAIL
PWRB
PWRM
supply voltage against known references.
supply.
falls, the first threshold is reached and PWRDN
Example of strategy for slow supplies
Fig.11 Example of power-down strategy with slow supplies.
delay while XA in
interrupt routine
CC(core)
supply
V t1
22
At the end of the interrupt routine, the firmware places the
SAA1575HL into reset. As V
second threshold is reached and is taken LOW. This
toggles the power controls, both PWRM and PWRB, and
will force a reset if it has not already occurred.
On power-up, the power controls both PWRM and PWRB
will be switched once the second threshold voltage is
reached. As the supply voltage rises further, the first
voltage threshold will be reached at which time both
PWRDN and PWRFAIL will be HIGH. This starts the reset
counter and the SAA1575HL will remain in reset until a set
time after this, depending on the state of the input pin
RSTIME.
V t2
reset timer delay
set by RSTIME
CC(P)
continues to fall, the
SAA1575HL
Product specification
MHB470