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BD3004HFP

Regulators with Voltage Detector and Watchdog Timer

ROHM Semiconductor 

zSetting of heat

2.0

ROHM standard board

Board size: 70 mm × 70 mm × 1.6 mm

1.6

θja = 78.1 (°C /W)

1.2

0.8

0.4

0

0 25 50 75 100 125 150

AMBIENT TEMPERATURE: Ta [℃]

Fig.17

Refer to the dissipation reduction illustrated in Fig.17 when using the IC in an environment where Ta ≥ 25°C. The characteristics of the IC are

greatly influenced by the operating temperature. If the temperature exceeds the maximum junction temperature Tjmax, the elements of the IC

may be damaged. It is necessary to give sufficient consideration to the heat of the IC in view of two points, i.e., the protection of the IC from

instantaneous damage and the maintenance of the reliability of the IC in long-time operation.

In order to protect the IC from thermal destruction, the operating temperature of the IC must not exceed the maximum junction temperature

Tjmax. Fig.17 illustrates the power dissipation/heat mitigation characteristics for the HRP-7 package. Always operate the IC within the power

dissipation (Pd). The following method is used to calculate the power consumption Pc (W).

Pc = (Vcc − VOUT) × IOUT + Vcc × Icc

Power dissipation Pd ≤ Pc

The load current Io is obtained to operate the IC within the power dissipation.

Vcc : Input voltage

VOUT : Output voltage

IOUT : Load current

Icc : Total supply current

IOUT ≤

Pd – Vcc × Icc

Vcc − VOUT

For Icc, see Fig. 1.

From the above, the maximum load current IOUTmax for the applied voltage Vcc can be calculated during the thermal design process.

Calculation example

Example: at Ta = 85°C, Vcc = 12 V, VOUT = 5 V

IOUT≤

0.832 − 12 × Icc

12 − 5

IOUT ≤ 118 mA (Icc = 80 µA)

θja = 78.1°C/W → −12.8 mW/°C

25°C = 1.6 W → 85°C = 0.832 mW

Make a thermal calculation in consideration of the above equations so that the whole operating temperature range will be within the power

dissipation. The power consumption Pc of the IC, in the event of shorting (i.e., if the Vo and GND pins are shorted), will be obtained from the

following equation:

Pc = Vcc × (Icc + Ishort) Ishort = Short current

zExternal settings for pins and precautions

1) Vcc pin

Insert capacitors with a capacitance of 0.33 µF to 1,000 µF between the Vcc and GND pins.

The capacitance varies with the application. Be sure to design the capacitance with a sufficient margin.

2) Output pin

Capacitors for stopping oscillation must be placed between each output pin and the GND pin. Capacitor capacitance values can be

used in a range between 0.1 µF and 1,000 µF. Since oscillation does not occur even for ESR values from 0.001 Ω to 100 Ω, a ceramic

capacitor can be used. Abrupt input voltage and load fluctuations can affect output voltages. Output capacitor capacitance values

should be determined after sufficient testing of the actual application

3) CT pin

Be sure to connect a capacitor to the CT pin. The reset output delay time is given by equation (1) on P. 5. The WDT time is given by

equations (2) and (3) on P.5. The setting times are proportional to the capacitance value of CT pin from the equations, so the maximum

and minimum setting times can be calculated from the electrical characteristics according to the capacitance. Note however that the

electrical characteristics do not include the external capacitor's temperature characteristics. The recommended connection capacity for

the CT pin is 0.001 µF to 22 µF.

6/8

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