ADSP-21486KSWZ-2AB datasheet(57/68 Pages) AD

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ADSP-21483/ADSP-21486/ADSP-21487/ADSP-21488/ADSP-21489

Rev. B

Page 57 of 68

March 2013

Note that the thermal characteristics values provided in

Table 56 and Table 57 are modeled values.

Thermal Diode

The ADSP-2148x processors incorporate thermal diode/s to

monitor the die temperature. The thermal diode of is a

grounded collector, PNP Bipolar Junction Transistor (BJT). The

THD_P pin is connected to the emitter and the THD_M pin is

connected to the base of the transistor. These pins can be used

by an external temperature sensor (such as ADM 1021A or

LM86 or others) to read the die temperature of the chip.

The technique used by the external temperature sensor is to

measure the change in VBE when the thermal diode is operated

at two different currents. This is shown in the following

equation:

where:

n = multiplication factor close to 1, depending on process

variations

k = Boltzmann’s constant

T = temperature (°C)

q = charge of the electron

N = ratio of the two currents

The two currents are usually in the range of 10 micro Amperes

to 300 micro Amperes for the common temperature sensor

chips available.

Table 58 contains the thermal diode specifications using the

transistor model.

Table 56. Thermal Characteristics for 100-Lead LQFP_EP

Parameter

Condition

Typical

Unit

JA

Airflow = 0 m/s

17.8

°C/W

JMA

Airflow = 1 m/s

15.4

°C/W

JMA

Airflow = 2 m/s

14.6

°C/W

JC

2.4

°C/W

JT

Airflow = 0 m/s

0.24

°C/W

JMT

Airflow = 1 m/s

0.37

°C/W

JMT

Airflow = 2 m/s

0.51

°C/W

Table 57. Thermal Characteristics for 176-Lead LQFP_EP

Parameter

Condition

Typical

Unit

JA

Airflow = 0 m/s

16.9

°C/W

JMA

Airflow = 1 m/s

14.6

°C/W

JMA

Airflow = 2 m/s

13.8

°C/W

JC

2.3

°C/W

JT

Airflow = 0 m/s

0.21

°C/W

JMT

Airflow = 1 m/s

0.32

°C/W

JMT

Airflow = 2 m/s

0.41

°C/W

V

------

In(N)



Table 58. Thermal Diode Parameters – Transistor Model1

Symbol

Parameter

Min

Typ

Max

Unit

IFW

Forward Bias Current

300

μA

Emitter Current

300

μA

3, 4

Transistor Ideality

1.012

1.015

1.017

3, 5

Series Resistance

0.12

0.2

0.28

1 See Engineer-to-Engineer Note “Using the On-Chip Thermal Diode on Analog Devices Processors” (EE-346).

2 Analog Devices does not recommend operation of the thermal diode under reverse bias.

3 Specified by design characterization.

4 The ideality factor, nQ, represents the deviation from ideal diode behavior as exemplified by the diode equation: IC = IS × (e qVBE/nqkT –1) where IS = saturation current,

q = electronic charge, VBE = voltage across the diode, k = Boltzmann Constant, and T = absolute temperature (Kelvin).

5 The series resistance (RT) can be used for more accurate readings as needed.

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