FAQ for FR Family
A/D converter
- What output impedance is recommended for the A/D pin ? (Target: MB91350A series)
- It is described that AVRH should be powered on after Vcc (Vcc → AVcc → AVRH). Is there any rule about time? Is there also any rule on the sequence for power-off ? (Target: MB91150 series)
- Is there any problem in powering on Vcc and AVRH at the same time? (Vcc is connected to AVcc and AVRH.) ? (Target: MB91150 series)
- Is there any problem in powering on Vcc and AVRH at the same time? (Vcc is connected to AVcc and AVRH.) ?
What output impedance is recommended for the A/D pin? (Target: MB91350Aseries)
- Answer :
The output impedance value varies depending on the peripheral clock and sampling time. When the peripheral clock is at 25 MHz and the sampling time is 440 ns (SMP = 5), the value is up to:
t = CR = 440/8 = 55 ns
(55 ns / 44 pF) - 360 Ω ≈ 890 Ω
(C0 + C1 = 44 pF, RON1 + RON2 = 360 Ω)
It is described that AVRH should be powered on after Vcc (Vcc → AVcc → AVRH). Is there any rule about time? Is there also any rule on the sequence for power-off ? (Target: MB91150series)
- Answer :
There is no rule about time.
However, if they are not powered on in the specified order or at the same time, a latch-up may occur.
Is there any problem in powering on Vcc and AVRH at the same time? (Vcc is connected to AVcc and AVRH.)? (Target: MB91150series)
- Answer :
There is no problem if they are powered on exactly at the same time. There seems to be no problem when Vcc and AVRH are supplied from the same interconnect.
Is there any problem in powering on Vcc and AVRH at the same time? (Vcc is connected to AVcc and AVRH.) ?
- Answer :
A current is fed to the reference pin (AVR) at A/D conversion. If a pull-up resistor is inserted, the AVR supply voltage level is lowered. Therefore, it is recommended to use the pin by directly connecting to Vcc.
