MPC8358E datasheet(91/95 Pages) FREESCALE

91 / 95 page

MPC8358E PowerQUICC II Pro Processor Revision 2.1 PBGA Silicon Hardware Specifications, Rev. 3

Freescale Semiconductor

System Design Information

24.5

Output Buffer DC Impedance

The device drivers are characterized over process, voltage, and temperature. For all buses, the driver is a

push-pull single-ended driver type (open drain for I2C).

To measure Z0 for the single-ended drivers, an external resistor is connected from the chip pad to OVDD

or GND. Then, the value of each resistor is varied until the pad voltage is OVDD/2 (see Figure 55). The

output impedance is the average of two components, the resistances of the pull-up and pull-down devices.

When data is held high, SW1 is closed (SW2 is open) and RP is trimmed until the voltage at the pad equals

OVDD/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, Z0 = (RP + RN)/2.

Figure 55. Driver Impedance Measurement

The value of this resistance and the strength of the driver’s current source can be found by making two

measurements. First, the output voltage is measured while driving logic 1 without an external differential

termination resistor. The measured voltage is V1 = Rsource × Isource. Second, the output voltage is measured

while driving logic 1 with an external precision differential termination resistor of value Rterm. The

measured voltage is V2 = 1/(1/R1 +1/R2)) × Isource. Solving for the output impedance gives Rsource =

Rterm × (V1/V2 – 1). The drive current is then Isource =V1/Rsource.

Table 77 summarizes the signal impedance targets. The driver impedance are targeted at minimum VDD,

nominal OVDD, 105°C.

Table 77. Impedance Characteristics

Impedance

Local Bus, Ethernet, DUART,

Control, Configuration, Power

Management

PCI

DDR DRAM

Symbol

Unit

42 Target

25 Target

20 Target

42 Target

25 Target

20 Target

OVDD

OGND

Pad

Data

SW1

SW2

MPC8358E Datasheet(PDF) 91 Page - Freescale Semiconductor, Inc

MPC8358E Datasheet(HTML) 91 Page - Freescale Semiconductor, Inc

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 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95

Datasheet Download

Link URL