Analog Devices ADSP-21020 manual Capacitive Loading

Capacitive Loading

Output delays are based on standard capacitive loads: 100 pF on address, select, page and strobe pins, and 50 pF on all others (see Figure 14). For different loads, these timing parameters should be derated. See the Hardware Configuration chapter of the ADSP-21020 User’s Manual for further information on derating of timing specifications.

Figures 16 and 17 show how the output rise time varies with capacitance. Figures 18 and 19 show how output delays vary with capacitance. Note that the graphs may not be linear outside the ranges shown.

	10
	9									9.18
2.0V)	8							1
	7
–
(0.8V	6
– ns	5
										3.95
TIME	4
								2
RISE	3
	2		1.46
	1		1.31
	0
		25		50	75	100	125	150	175	200
					LOAD CAPACITANCE – pF

NOTES:

(1)OUTPUT PINS BG, TIMEXP

(2)OUTPUT PINS PMD47–0, DMD39–0, FLAG3–0

Figure 16. Typical Output Rise Time vs. Load Capacitance (at Maximum Case Temperature)

2.0V)	4								3.59
–
							1
(0.8V	3
– ns									3.00
	2						2
TIME		1.33
RISE	1	0.85
	0									π
	25		50	75	100	125	150	175	200

LOAD CAPACITANCE – pF

NOTES:

(1)OUTPUT PINS PMA23–0, PMS1–0, PMPAGE, DMA31–0, DMS3–0, DMPAGE, TDO

(2)OUTPUT PINS PMRD, PMWR, DMRD, DMWR

Figure 17. Typical Output Rise Time vs. Load Capacitance (at Maximum Case Temperature)

ADSP-21020

	12									11.19
– ns	10
HOLDOR	8
DELAY								1
	6									5.34
OUTPUT
	4							2
	2
NOMINAL			– 0.89
	–2		–1.86
		25		50	75	100	125	150	175	200

LOAD CAPACITANCE – pF

NOTES:

(1)OUTPUT PINS BG, TIMEXP

(2)OUTPUT PINS PMD47–0, DMD39–0, FLAG3–0

Figure 18. Typical Output Delay or Hold vs. Load Capacitance (at Maximum Case Temperature)

– ns	3								2.99
								1
HOLD	2
									2.27
OR	1							2
DELAY	NOMINAL
OUTPUT	–1	– 1.70
	–2
		– 2.24
	–3
	25		50	75	100	125	150	175	200

LOAD CAPACITANCE – pF

NOTES:

(1)OUTPUT PINS PMA23–0, PMS1–0, PMPAGE, DMA31–0, DMS3–0, DMPAGE, TDO

(2)OUTPUT PINS PMRD, PMWR, DMRD, DMWR

Figure 19. Typical Output Delay or Hold vs. Load Capacitance (at Maximum Case Temperature)

REV. C –25–