PC7447AMGH1000LB datasheet(38/44 Pages) ATMEL

38 / 44 page

5387B–HIREL–07/05

PC7447A [Preliminary]

Power and ground connections must be made to all external V

DD, OVDD, and GND pins in the

PC7447A.

For backward compatibility with the PC7447 to the PC7447A, the new power and ground signals

(formerly NC, see Table 8-1 on page 21) may be left unconnected. There is no performance

degradation associated with leaving these pins unconnected. However, future devices may

require these additional power and ground signals to be connected to achieve maximum perfor-

mance, and it is recommended that new designs include the additional connections to facilitate

future upgrades. See also section ”Pinout Listings” on page 21 for additional information.

13.5 Output Buffer DC Impedance

The PC7447A processor bus drivers are characterized over process, voltage, and temperature.

To measure Z

0, an external resistor is connected from the chip pad to OVDD or GND. The value

of each resistor is varied until the pad voltage is OV

DD/2. Figure 13-2 on page 38 shows the

driver impedance measurement.

The output impedance is the average of two components–the resistances of the pull-up and pull-

down devices. When data is held low, SW2 is closed (SW1 is open), and R

N is trimmed until the

voltage at the pad equals OV

DD/2. RN then becomes the resistance of the pull-down devices.

When data is held high, SW1 is closed (SW2 is open), and R

P is trimmed until the voltage at the

pad equals OV

DD/2. RP then becomes the resistance of the pull-up devices. RP and RN are

designed to be close to each other in value. Then, Z

0 = (RP + RN)/2.

Figure 13-2. Driver Impedance Measurement

Table 13-2 summarizes the signal impedance results. The impedance increases with junction

temperature and is relatively unaffected by bus voltage.

Table 13-2.

Impedance Characteristics with V

DD = 1.5V, OVDD = 1.8V ±5%, Tj = 5° - 85°C

Impedance

Processor bus

L3 Bus

Unit

Typical

33 – 42

34 – 42

Ω

Maximum

31 – 51

32 – 44

Ω

OVDD

OGND

SW2

SW1

Pad

Data

PC7447AMGH1000LB Datasheet(PDF) 38 Page - ATMEL Corporation

PC7447AMGH1000LB Datasheet(HTML) 38 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Datasheet Download

Link URL