38K2 datasheet(147/358 Pages) RENESAS

147 / 358 page

NOTES ON USAGE/DATA REQUIRED FOR MASK ORDERS

Rev.2.00

Oct 15, 2006

page 128 of 130

38K2 Group

REJ09B0338-0200

HARDWARE

NOTES ON USAGE

Power Source Voltage

When the power source voltage value of a microcomputer is less

than the value which is indicated as the recommended operating

conditions, the microcomputer does not operate normally and may

perform unstable operation.

In a system where the power source voltage drops slowly when

the power source voltage drops or the power supply is turned off,

reset a microcomputer when the power source voltage is less than

the recommended operating conditions and design a system not

to cause errors to the system by this unstable operation.

Handling of Power Source Pin

In order to avoid a latch-up occurrence, connect a capacitor suit-

able for high frequencies as bypass capacitor between power

source pin (Vcc pin) and GND pin (Vss pin). Besides, connect the

capacitor to as close as possible. For bypass capacitor which

should not be located too far from the pins to be connected, a ce-

ramic or electrolytic capacitor of 1.0

µF is recommended.

USB Port Pins (D0+, D0-, D1+, D1-, D2+, D2-)

Treatment

•The USB specification requires a driver-impedance 28 to 44

Ω. In

order to meet the USB specification impedance requirements,

connect a resistor (27

Ω recommended) in series to the USB port

pins.

In addition, in order to reduce the ringing and control the falling/

rising timing and a crossover point, connect a capacitor between

the USB port pins and the Vss pin if necessary.

The values and structure of those peripheral elements depend on

the impedance characteristics and the layout of the printed circuit

board. Accordingly, evaluate your system and observe waveforms

before actual use and decide use of elements and the values of

resistors and capacitors.

•Make sure the USB D+/D- lines do not cross any other wires.

Keep a large GND area to protect the USB lines. Also, make sure

you use a USB specification compliant connecter for the connec-

tion.

USBVREF pin Treatment (Noise Elimination)

•Connect a capacitor between the USBVREF pin and the Vss pin.

The capacitor should have a 2.2

µF capacitor (electrolytic capaci-

tor) and a 0.1

µF capacitor (ceramic type capacitor) connected in

parallel.

•In Vcc = 3.0 to 3.6 V operation, connect the USBVREF pin directly

to the Vcc pin in order to supply power to the USB port circuit. In

addition, you will need to disable the built-in USB reference volt-

age circuit in this operation (set bit 4 of the USB control register

to “0”.) If you are using the bus powered supply in this condition,

the DC-DC converter must be placed outside the MCU.

•In Vcc = 4.00 to 5.25 V operation, do not connect the external

DC-DC converter to the USBVREF pin. Use the built-in USB refer-

ence voltage circuit.

USB Communication

In applications requiring high-reliability, we recommend providing

the system with protective measures such as USB function initial-

ization by software or USB reset by the host to prevent USB

communication from being terminated unexpectedly, for example

due to external causes such as noise.

Flash Memory Version

The CNVss pin is connected to the internal memory circuit block

by a low-ohmic resistance, since it has the multiplexed function to

be a programmable power source pin (VPP pin) as well.

To improve the noise reduction, connect a track between CNVss

pin and Vss pin or Vcc pin with 1 to 10 k

Ω resistance.

The mask ROM version track of CNVss pin has no operational in-

terference even if it is connected to Vss pin or Vcc pin via a

resistor.

Electric Characteristic Differences Between

Mask ROM and Flash Memory Version MCUs

There are differences in electric characteristics, operation margin,

noise immunity, and noise radiation between Mask ROM and

Flash Memory version MCUs due to the difference in the manufac-

turing processes.

When manufacturing an application system with the Flash

Memory version and then switching to use of the Mask ROM ver-

sion, please perform sufficient evaluations for the commercial

samples of the Mask ROM version.

DATA REQUIRED FOR MASK ORDERS

The following are necessary when ordering a mask ROM produc-

tion:

1. Mask ROM Order Confirmation Form✽

2. Mark Specification Form✽

3. Data to be written to ROM, in EPROM form (three identical cop-

ies) or one floppy disk.

✽ For the mask ROM confirmation and the mark specifications, re-

fer to the “Renesas Technology Corp.” Homepage

(http://www.renesas.com).

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