4 Reset Generation
25
CW6632B Bluetooth 3.0 Audio Player SOC
Version 1.0.0
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4
Reset Generation
4.1
Power-on Reset (POR)
CW6632B provides an on-chip Power-On-Reset (POR) circuit to detect power-on and to reset internal logic before
VDD reaches the pre-determined POR threshold voltage. When VDD=1.2V, the POR threshold voltage is set to be
about 0.7V~0.9V.
Sometimes, when the VDD is power-off and quickly power-on again, there might be cases that the POR will work
improperly and internal reset might not be generated. For this reason, CW6632B POR circuit incorporates an
internal self-reset module to discharge PORB output during power-off to ensure each power cycle will work properly.
However, it is also highly recommended user should have a long time between power-off and next power-on to
ensure proper start-up. The time depends on actual system board environment and how much decoupling
capacitors between power and ground. User has to take into account this effect during board level design.
illustrates the power-on and reset signals waveform during proper power-on. Internally, there is TPOR
and TRC time for both the POR circuit and the internal counter. TPOR is the time for the POR circuit to stay at zero
voltage until it reaches VPOR and the time varies for different VDD rise-up time. It can be assumed to be about 2/3
of the VDD rise-up time. TRC is the time for internal counter to count 4ms using internal RC-oscillator when the
counter sees a high logic from PORB signal. As a result, the overall internal reset time is the sum of TPOR and TRC.
Such a long time is required to ensure the Power is stable for system use. It also ensures all internal logics are
properly reset.
Power-on-reset
trigger point
Browm-out-reset
trigger point
VDD
1.2V
PORB
0 V
Figure 4-1 Power on reset
4.2
System Reset
All reset signals are OR‟ed together inside the device to generate an overall system reset to reset the chip. Once
reset, the program memory address is reset to 8000h, which is the start address of the Normal Mode.
illustrates the reset sources.