MC34708 datasheet(16/159 Pages) FREESCALE

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Analog Integrated Circuit Device Data



Freescale Semiconductor

MC34708

General Product Characteristics

5.2.1

Power Dissipation

During operation, the temperature of the die should not exceed the maximum junction temperature. To optimize the thermal

management scheme and avoid overheating, the MC34708 PMIC provides a thermal management system. The thermal

protection is based on a circuit with a voltage output proportional to the absolute temperature.This voltage can be read out via

the ADC for specific temperature readouts, see Channel 3 Die Temperature.

The ADEN SPI bit must be set = 1 to enable the comparators for the thermal monitoring (THERM110, THERM120, THERM125,

THERM130, and thermal shutdown). With ADEN = 0 the thermal monitors and thermal shutdown are disabled. Interrupts

THERM110, THERM120, THERM125, and THERM130 will be generated when respectively crossing in either direction the

thresholds specified in Table 6. The temperature range can be determined by reading the THERMxxxS bits.

Thermal protection is integrated to power off the MC34708 PMIC and disables the charger circuitry in case of over dissipation.

This thermal protection will act above the maximum junction temperature to avoid any unwanted power downs. The protection is

debounced for 8.0 ms in order to suppress any (thermal) noise. This protection should be considered as a fail-safe mechanism

and therefore the application design should be dimensioned such that this protection is not tripped under normal conditions. The

temperature thresholds and the sense bit assignment are listed in Table 6

The THERM1xx thresholds are debounced by the SPI bits DIE_TEMP_DB[1:0], which are programmable from 100

s to 4.0 ms

(4.0 ms by default), see Table 7. When the die temperature crosses these thresholds, the corresponding sense bit will change

and an interrupt will be generated to notify the software that the hardware is reaching its thermal limit.

Table 6. Thermal Protection Thresholds

Parameter

Min

Typ

Max

Units

Notes

Thermal 110 °C threshold (THERM110)

105

110

115

°C

Thermal 120 °C threshold (THERM120)

115

120

125

°C

Thermal 125 °C threshold (THERM125)

120

125

130

°C

Thermal 130 °C threshold (THERM130)

125

130

135

°C

Thermal warning hysteresis

2.0

4.0

°C

(12)

Thermal protection threshold

130

140

150

°C

Notes

12.

Equivalent to approx. 30 mW min, 60 mW max

Table 7. Die Temp Debounce Settings

DIE_TEMP_DB [1:0]

Time

Units

0.100

1.0

2.5

11 (default)

4.0

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