MPC5607B datasheet(39/110 Pages) FREESCALE

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Electrical characteristics

MPC5607B Microcontroller Data Sheet, Rev. 6

Freescale Semiconductor

4.5

Thermal characteristics

4.5.1

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 14 LQFP thermal characteristics, considering a thermal resistance of 144 LQFP as 48.3 °C/W, at ambient

temperature TA = 125 °C, the junction temperature Tj will cross 150 °C if the total power dissipation is greater than

(150 – 125)/48.3 = 517 mW. Therefore, the total device current IDDMAX at 125 °C/5.5 V 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 4.5.2, “Package thermal characteristics, it is

recommended to use this resistor only in the 125 °C/5.5 V 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  resistor can be used.

•If IDD(VDD_BV) > 90 mA, then 8  resistor can be used.

Using resistance in the range of 4–8

, the gain will be around 10–20% of total consumption on VDD_BV. For example, if 8 

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.

In order to ensure correct power up, the minimum VDD_BV to be guaranteed is 30 ms/V. If the supply ramp is slower than this

value, then LVDHV3B monitoring ballast supply VDD_BV pin gets triggered leading to device reset. Until the supply reaches

certain threshold, this low voltage detector (LVD) generates destructive reset event in the system. This threshold depends on

the maximum IDD(VDD_BV) possible across the external resistor.

4.5.2

Package thermal characteristics

Table 14. LQFP thermal characteristics1

Symbol

Parameter

Conditions2

Pin count

Value

Unit

Min Typ Max

RJA CC D Thermal resistance,

junction-to-ambient natural

convection3

Single-layer board — 1s

100

—

°C/W

144

—

176

—

Four-layer board — 2s2p

100

—

49.7

144

—

48.3

176

—

47.3

RJB CC

Thermal resistance,

junction-to-board4

Single-layer board — 1s

100

—

°C/W

144

—

176

—

Four-layer board — 2s2p

100

—

33.6

144

—

33.4

176

—

33.4

MPC5607B Datasheet(PDF) 39 Page - Freescale Semiconductor, Inc

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