SPC5705BECLLR datasheet(17/92 Pages) FREESCALE

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Electrical characteristics

MPC5607B Microcontroller Data Sheet, Rev. 3

Preliminary—Subject to Change Without Notice

Freescale Semiconductor

3.5

Thermal characteristics

3.5.1

External ballast resistor recommendations

External ballast resistor on VDD_BV pin helps in reducing the overall power dissipation inside the device. This resistor is

required only when maximum power consumption exceeds the limit imposed by package thermal characteristics.

As stated in Table 10 LQFP thermal characteristics, considering thermal resistance of LQFP144 as 48.3 °C/W, at ambient TA =

125 °C, the junction temp Tj will cross 150 °C if total power dissipation > (150 - 125)/48.3 = 517 mW. Therefore, total device

current IDDMAX at 125 °C/5.5V must not exceed 94.1 mA (i.e. PD/VDD). Assuming an average IDD(VDD_HV) of 15-20 mA

consumption typically during device RUN mode, the LV domain consumption IDD(VDD_BV) is thus limited to IDDMAX -

IDD(VDD_HV) i.e. 80 mA.

Therefore, respecting the maximum power allowed as explained in Section 3.5.2, “Package thermal characteristics, it is

recommended to use this resistor only in the 125 °C/5.5V operating corner as per the following guidelines:

•If IDD(VDD_BV) < 80 mA, then no resistor is required.

•If 80 mA < IDD(VDD_BV) < 90 mA, then 4 Ohm resistor can be used along with 14.7 µf decoupling.

•If IDD(VDD_BV) > 90 mA, then 8 Ohm resistor can be used along with 33 µf decoupling.

Using resistance in the range of 4-8 Ohm, the gain will be around 10-20% of total consumption on VDD_BV. For example, if 8

Ohm resistor is used, then power consumption when IDD(VDD_BV) is 110 mA is equivalent to power consumption when

IDD(VDD_BV) is 90 mA (approximately) when resistor not used.

3.5.2

Package thermal characteristics

Table 10. LQFP thermal characteristics1

1 Thermal characteristics are targets based on simulation that are subject to change per device characterization.

Symbol

Parameter Conditions2

2 V

DD = 3.3 V ± 10% / 5.0 V ± 10%, TA = −40 to 125 °C.

Pin count

Value3

3 All values need to be confirmed during device validation.

Unit

Min

Typ

Max

RθJA

Thermal

resistance,

junction-to-

ambient

natural

convection4

4 Junction-to-ambient thermal resistance determined per JEDEC JESD51-3 and JESD51-6. Thermal test board meets

JEDEC specification for this package. When Greek letters are not available, the symbols are typed as RthJA and RthJMA.

Single-layer

board—1s

100

—

°C/W

144

—

176

—

Four-layer

board—2s2p

100

—

49.7

144

—

48.3

176

—

47.3

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