PD64A_15 Datasheet, PDF (30/66 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCONTROLLERS FOR INFRARED REMOTE CONTROL TRANSMISSION

µPD64A, 65
7.1 Functions of POC Circuit
The POC circuit has the following functions.
• Generates an internal reset signal when VDD ≤ VPOC.
• Cancels an internal reset signal when VDD > VPOC.
Here, VDD: Power supply voltage, VPOC: POC detection voltage.
VDD
3.6 V
2.0 V
VPOC
Operating ambient temperature TA = –40 to +85°C
Clock frequency fX = 2.4 to 8 MHz
←POC detection voltage VPOC = 1.85 V (TYP.)^{Note 3}
Approx. 1.7 V
0V
→t
Internal reset signal
Reset
↑
Note 1
Operating mode
↑ Reset
Note 2
Notes 1. In reality, an oscillation stabilization wait time must elapse before the circuit is switched to operating
mode. The oscillation stabilization wait time is about 246/fX to 694/fX (about 70 to 190 µs, at fX = 3.64
MHz).
2. For the POC circuit to generate an internal reset signal when the power supply voltage has fallen,
it is necessary for the power supply voltage to be kept less than the VPOC for a period of 1 ms or more.
Therefore, in reality, there is a time lag of up to 1 ms until the reset takes effect.
3. The POC detection voltage (VPOC) varies between approximately 1.7 to 2.0 V; thus, the reset may
be canceled at a power supply voltage smaller than the assured range (VDD = 2.0 to 3.6 V). However,
as long as the conditions for operating the POC circuit are met, the actual lowest operating power
supply voltage is lower than the POC detection voltage. Therefore, no malfunction occurs due to the
shortage of power supply voltage. However, malfunction for such reasons as the clock not oscillating
due to low power supply voltage may occur (refer to Cautions 3. in 7. POC CIRCUIT).
7.2 Oscillation Check at Low Supply Voltage
A reliable reset operation can be expected from the POC circuit if it satisfies the condition that the clock can
oscillate even at a low power supply voltage (the oscillation start voltage of the resonator being even lower than
the POC detection voltage). Whether this condition is met or not can be checked by measuring the oscillation status
on a product which actually contains a POC circuit, as follows.
<1> Connect a storage oscilloscope to the XOUT pin so that the oscillation status can be measured.
<2> Connect a power supply whose output voltage can be varied and then gradually raise the power supply
voltage VDD from 0 V (making sure to avoid VDD > 3.6 V).
At first (when VDD < approx. 1.7 V), the XOUT pin is 0 V regardless of the VDD. However, at the point when VDD
reaches the POC detection voltage (VPOC = 1.85 V (TYP.)), the voltage of the XOUT pin jumps to about 0.5VDD.
Maintain this power supply voltage for a while to measure the waveform of the XOUT pin. If, by any chance, the
oscillation start voltage of the resonator is lower than the POC detection voltage, the growing oscillation of the XOUT
pin can be confirmed within several ms after VDD has reached VPOC.
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Data Sheet U14380EJ3V0DS00