Datasheet
Analog Integrated Circuit Device Data
17 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 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 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
(14)
Thermal protection threshold
130 140 150 °C
Notes
14. Equivalent to approx. 30 mW min, 60 mW max
Table 7. Die Temp Debounce Settings
DIE_TEMP_DB [1:0] Time Units
00 0.100 ms
01 1.0 ms
10 2.5 ms
11 (default) 4.0 ms