Data Sheet

VS1000 Datasheet
3 CHARACTERISTICS & SPECIFICATIONS
3.8 Power-On Reset
Because the VS1000 contains its own regulators, special care must be taken to guarantee a
good reset state during the power-up. The voltage on the xRESET pin has to remain sufficiently
lower than the IOVDD voltage until the IOVDD and CVDD voltages have risen high enough to
be able to reset and hold the reset state.
The suggested connection (schematics in Section 5) is to connect the xRESET signal with a
100kΩ resistor to IOVDD and a 10µF capacitor to ground. This should provide a sufficient delay
in a full power-up situation.
Figure 2: VS1000 Typical Power-up.
The above example picture shows a typical power-up sequence. A PWRBTN signal (not shown)
is generated from VHIGH using a RC as discussed in Section 3.7. When both VHIGH and
PWRBTN are active, the AVDD, IOVDD and CVDD regulators start (IOVDD shown). The
IOVDD regulator starts in 1.8 V mode. Because xRESET stays below 0.3×IOVDD by the RC
at the beginning of the power-up, xRESET needs to reach 0.7×IOVDD before RESET is de-
asserted. After that happens, the oscillator amplifier leaves reset state, and the oscillator starts.
When the amplitude of the oscillation is sufficient, the VS1000 leaves reset. At this moment, all
peripheral pins that are normally outputs switch from high-impedance state to output mode in
their default states. The TX pin is shown as an example. TX becomes an output and is driven
high when VS1000 leaves the reset state. If GPIO0_7 contains a pull-up resistor, the IOVDD
regulator is configured to 3.3V, which can also be seen.
Note that the passive RC circuit generates a reset only when power-up is performed from a
total power-off state. If there are residual voltages in the system (such as during an intermittent
supply voltage drop, or an external circuit driving any IO pin of VS1000), the relative levels of
xRESET and IOVDD/CVDD may no longer fulfill the <0.3×IOVDD condition to create a good
reset. You will need an external voltage monitor chip connected to xRESET or control
xRESET using your microcontroller in any application where short power interruptions
are possible.
Version: 1.5, 2016-06-09 9