ADSP-2104 datasheet(15/36 Pages) AD

15 / 36 page

ADSP-2104/ADSP-2109

REV. 0

–15–

TEST CONDITIONS

Figure 10 shows voltage reference levels for ac measurements.

3.0V

1.5V

0.0V

2.0V

1.5V

0.8V

INPUT

OUTPUT

Figure 10. Voltage Reference Levels for AC Measurements

(Except Output Enable/Disable)

Output Disable Time

Output pins are considered to be disabled when they have

stopped driving and started a transition from the measured

output high or low voltage to a high impedance state. The

output disable time (tDIS) is the difference of tMEASURED and

tDECAY, as shown in Figure 11. The time tMEASURED is the

interval from when a reference signal reaches a high or low

voltage level to when the output voltages have changed by 0.5 V

from the measured output high or low voltage.

The decay time, tDECAY, is dependent on the capacitative load,

CL, and the current load, iL, on the output pin. It can be

approximated by the following equation:

DECAY =

L × 0.5 V

from which

tDIS = tMEASURED – tDECAY

is calculated. If multiple pins (such as the data bus) are dis-

abled, the measurement value is that of the last pin to stop

driving.

Output Enable Time

Output pins are considered to be enabled when they have made

a transition from a high-impedance state to when they start

driving. The output enable time (t ENA) is the interval from

when a reference signal reaches a high or low voltage level to

when the output has reached a specified high or low trip point,

as shown in Figure 11. If multiple pins (such as the data bus)

are enabled, the measurement value is that of the first pin to

start driving.

SPECIFICATIONS (ADSP-2104/ADSP-2109)

Figure 12. Equivalent Device Loading for AC Measurements

(Except Output Enable/Disable)

2.0V

1.0V

tENA

REFERENCE

SIGNAL

OUTPUT

tDECAY

VOH (MEASURED)

OUTPUT STOPS

DRIVING

OUTPUT STARTS

DRIVING

tDIS

tMEASURED

VOL (MEASURED)

VOH (MEASURED) – 0.5V

VOL (MEASURED) +0.5V

HIGH-IMPEDANCE STATE.

TEST CONDITIONS CAUSE

THIS VOLTAGE LEVEL TO BE

APPROXIMATELY 1.5V.

VOH (MEASURED)

VOL (MEASURED)

Figure 11. Output Enable/Disable

OUTPUT

50pF

+1.5V

IOH

IOL

ADSP-2104 Datasheet(PDF) 15 Page - Analog Devices

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