ADSP-21MOD870_15 Datasheet, PDF (17/32 Pages) Analog Devices – Internet Gateway Processor

OUTPUT DRIVE CURRENTS
Figure 14 shows typical I-V characteristics for the output driv-
ers of the ADSP-21mod870. The curves represent the current
drive capability of the output drivers as a function of output
voltage.
80
60
3.6V, –40°C
40
20
0
3.0V, +85°C
3.3V, +25°C
–20
3.0V, +85°C
–40
3.3V, +25°C
–60
–80 ₀
3.6V, –40°C
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
SOURCE VOLTAGE – V
Figure 14. Typical Drive Currents
POWER DISSIPATION
To determine total power dissipation in a specific application,
the following equation should be applied for each output:
C × V_DD2 × f
C = load capacitance, f = output switching frequency.
Example
In an application where external data memory is used and no
other outputs are active, power dissipation is calculated as follows:
Assumptions
• External data memory is accessed every cycle with 50% of
the address pins switching.
• External data memory writes occur every other cycle with
50% of the data pins switching.
• Each address and data pin has a 10 pF total load at the pin.
• The application operates at V_DD = 3.3 V and t_CK = 30 ns.
Total Power Dissipation = P_INT + (C × V_DD² × f)
P_INT = internal power dissipation from Power vs. Frequency
graph (Figure 15).
(C × V_DD² × f) is calculated for each output:
# of
Pins
Address, DMS 8
Data Output, WR 9
RD
1
CLKOUT
1
؋C
× 10 pF
× 10 pF
× 10 pF
× 10 pF
؋ V_DD2
× 3.3² V
× 3.3² V
× 3.3² V
× 3.3² V
؋f
× 33.3² MHz = 29.0 mW
× 16.67 MHz = 16.3 mW
× 16.67 MHz = 1.8 mW
× 33.3 MHz = 3.6 mW
50.7 mW
Total power dissipation for this example is P_INT + 50.7 mW.
ADSP-21mod870
21mod870 POWER, INTERNAL^{1, 3, 4}
250
200
144mW
150
112.2mW
100
87mW
50
V_DD = 3.6V
V_DD = 3.3V
216mW
168.3mW
132mW
V_DD = 3.0V
0
33.3
52
1/t_CK – MHz
POWER, IDLE^{1, 2, 3}
45
40
35
V_DD = 3.3V
30
25mW
25
20
V_DD = 3.6V
V_DD = 3.0V
15
23mW
21mW
10
35mW
32mW
30mW
5
0
33.3
1/f_CK – MHz
52
POWER, IDLE n MODES³
45
40
35
32mW _IDLE
30
25
23mW
20
15
10mW
10
9mW
5
13mW _{IDLE (16)}
12mW ^{IDLE (128)}
0
33.3
52
1/f_CK – MHz
VALID FOR ALL TEMPERATURE GRADES.
1_{POWER REFLECTS DEVICE OPERATING WITH NO OUTPUT LOADS.}
2_{IDLE REFERS TO ADSP-21mod870 STATE OF OPERATION DURING EXECUTION OF}
IDLE INSTRUCTION. DEASSERTED PINS ARE DRIVEN TO EITHER V_DD OR GND.
3_{TYPICAL POWER DISSIPATION AT 3.3V VDD AND +25؇C, EXCEPT WHERE SPECIFIED.}
4_{IDD MEASUREMENT TAKEN WITH ALL INSTRUCTIONS EXECUTING FROM INTERNAL}
MEMORY. 50% OF THE INSTRUCTIONS ARE MULTIFUNCTION (TYPES 1, 4, 5, 12, 13, 14),
30% ARE TYPE 2 AND TYPE 6, AND 20% ARE IDLE INSTRUCTIONS.
Figure 15. Power vs. Frequency
REV. 0
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