DSP56721 datasheet(10/54 Pages) FREESCALE

10 / 54 page

SymphonyTM DSP56720 / DSP56721 Multi-Core Audio Processors, Rev.1

Freescale Semiconductor

2.1.2

Thermal Characteristics

For thermal characteristics, see Table 5.

2.1.3

Power Requirements

To prevent high current conditions due to possible improper sequencing of the power supplies, use an external Schottky diode

as shown in Figure 6, connected between the DSP56720/DSP56721 IO_VDD and Core_VDD power pins.

Figure 6. Prevent High Current Conditions by Using External Schottky Diode

If an external Schottky diode is not used (to prevent a high current condition at power-up), then IO_VDD must be applied ahead

of Core_VDD, as shown in Figure 7.

Figure 7. Prevent High Current Conditions by Applying IO_VDD Before Core_VDD

For correct operation of the internal power-on reset logic, the Core_VDD ramp rate (Tr) to full supply must be less than 10 ms,

as shown in Figure 8.

Table 5. Thermal Characteristics

Characteristic

Board Type

Symbol

LQFP Values

Unit

Natural Convection, Junction-to-ambient thermal resistance1,2

Single layer board

(1s)

RθJA or θJA

57 for 80 QFP

49 for 144 QFP

°C/W

Four layer board

(2s2p)

44 for 80 QFP

40 for 144 QFP

°C/W

Junction-to-case thermal resistance3

–RθJC or θJC 10 for 80 QFP

9 for 144 QFP

°C/W

Notes:

Junction temperature is a function of die size, on-chip power dissipation, package thermal resistance, mounting site (board)

temperature, ambient temperature, air flow, power dissipation of other components on the board, and board thermal resistance.

Per SEMI G38-87 and JEDEC JESD51-2 with the single layer board horizontal.

Thermal resistance between the die and the case top surface as measured by the cold plate method

(MIL SPEC-883 Method 1012.1).

IO_VDD

Core_VDD

External

Schottky

Diode

Core_VDD

IO_VDD

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