Data Sheet

VS1000 Datasheet
3 CHARACTERISTICS & SPECIFICATIONS
3.9 Power-Off
The power button pin (PWRBTN) turns the regulators on so that VS1000 can boot. When
asserted for more than 5.6 seconds it generates a watchdog-type reset to reboot the system.
Powering off, however, is performed by software. This prevents important data from being lost
when the user requests power off while for example writing to external memory.
The ROM firmware detects a request to power off from a long press (2 seconds) of the power
button. The power off function can also be called by user software. The default power off
routine performs the following steps.
• Switch to 1.0x clock and disable PLL. This reduces power consumption.
• Disable interrupts.
• Power down USB and analog drivers.
• Turn off LEDs - switch IO1_1(SCLK), IO1_2(SI) and IO1_3(SO) low.
• Wait that the power button is released. Otherwise the power button being asserted would
immediately force the regulators on again.
• Turn on watchdog with a 5-second interval if it isn’t already active.
• Keep shutting down the regulators until vs1000 powers down or gets a watchdog reset.
Because the CVDD voltage monitor uses a reference that is derived from AVDD, the core
voltage CVDD should drop sufficiently faster than AVDD so that the voltage monitor keeps the
reset asserted long enough. Thus the capacitance on CVDD should be significantly smaller
than in AVDD.
Note that when the CVDD monitor asserts reset, the current consumption of CVDD will drop
near zero. If necessary, a large resistor (1MΩ) can be added to CVDD to drop the voltage
faster.
If the supply voltage to VHIGH has a high internal impedance, such as batteries, the drop in
current consumption may cause the voltages to rise enough for the CVDD monitor to deassert
reset, causing a reboot of the system (which enables the regulators). With such a power source,
smaller bypass capacitors for the IOVDD voltage would stop the oscillator sooner and thus
prevent the vs1000 from leaving the reset state.
Version: 1.5, 2016-06-09 10