BA3258HFP,BA33D15HFP,BA33D18HFP

Technical Note

6/8

www.rohm.com

2011.03 - Rev.B

© 2011 ROHM Co., Ltd. All rights reserved.

●

Thermal Design

If the IC is used under excessive power dissipation conditions, the chip temperature will rise, which will have an adverse

effect on the electrical characteristics of the IC, such as a reduction in current capability. Furthermore, if the temperature

dissipation is within the permissible range in order to prevent instantaneous IC damage resulting from heat and maintain the

reliability of the IC for long-term operation. Refer to the power derating characteristics curves in Fig. 29.

・

Power Consumption (Pc) Calculation Method

・

Power consumption of 3.3V power transistor:

Pc1 = (Vcc − 3.3)

 Io1

・

Power consumption of Vo2 power transistor:

Pc2 = (Vcc − Vo2)

 Io2

・

Power consumption due to circuit current:

Pc3 = Vcc

 Icc

→

Pc = Pc1 + Pc2 + Pc3

Refer to the above and implement proper thermal designs so that the IC will not be used under excessive power dissipation

conditions under the entire operating temperature range.

・

Calculation example (BA33D15HFP)

Example: Vcc = 5V, Io1 = 200mA, and Io2 = 100mA

・

Power consumption of 3.3V power transistor:

Pc1 = (Vcc − 3.3)

 Io1 = (5 − 3.3)  0.2 = 0.34W

・

Power consumption of 1.5V power transistor:

Pc2 = (Vcc − 1.5)

 Io2 = (5 − 1.5)  0.2 = 0.35W

・

Power consumption due to circuit current: Pc3 = Vcc

 Icc = 5  0.0085 = 0.0425 (W) (See Figs. 14 and 15)

Implement proper thermal designs taking into consideration the dissipation at full power consumption

(i.e., Pc1 + Pc2 + Pc3 = 0.34 + 0.35 + 0.0425 = 0.7325W).

●

Explanation of External Components

○

BA3258HFP

1) Pin 1 (Vcc pin)

Connecting a ceramic capacitor with a capacitance of approximately 3.3

F between Vcc and GND as close to the pins

as possible is recommended.

2) Pins 4 and 5 (Vo pins)

Insert a capacitor between the Vo and GND pins in order to prevent output oscillation. The capacitor may oscillate if

the capacitance changes as a result of temperature fluctuations. Therefore, it is recommended that a ceramic

capacitor with a temperature coefficient of X5R or above and a maximum capacitance change (resulting from

temperature fluctuations) of

10% be used. The capacitance should be between 1F and 1,000µF. (Refer to Fig. 30)

○

BA33D□□Series

1) Pin 1 (Vcc pin)

Insert a 1

F capacitor between Vcc and GND. The capacitance will vary depending on the application. Check the

capacitance with the application set and implement designing with a sufficient margin.

2) Pins 4 and 5 (Vo pins)

Insert a capacitor between the Vo and GND pins in order to prevent oscillation. The capacitance may vary greatly with

temperature changes, thus making it impossible to completely prevent oscillation. Therefore, use a tantalum aluminum

electrolytic capacitor with a low ESR (Equivalent Serial Resistance). The output will oscillate if the ESR is too high or too

low, so refer to the ESR characteristcs in Fig. 31 and operate the IC within the stable operating region. If there is a

sudden load change, use a capacitor with higher capacitance.

A capacitance between 10

F and 1,000F is

recommended.

Fig. 29 Thermal Derating Curves

Fig. 30 BA3258HFP ESR characteristics

Fig. 31 BA33D□□ Series ESR

AMBIENT TEMPERATURE：Ta［℃］

8

10

9

7

6

5

4

3

2

1

0

25

50

75

100

125

150

Board size: 70 mm

 70  1.6 mm (with a thermal via incorporated by the board)

Board surface area: 10.5 mm

 10.5 mm

(1) 2-layer board (Backside copper foil area: 15 mm

 15mm)

(2) 2-layer board (Backside copper foil area: 70 mm

 70 mm)

(3) 4-layer board (Backside copper foil area: 70 mm

 70mm)

0

Io [mA]

200

400

600

800 1000

0

0.01

0.1

0.5

1.0

2.0

0.02

0.05

0.2

5.0

不安定領域

10.0

安定領域

0.15

4.0

不安定領域

200

400

600

800 1000

0

0.01

0.1

0.5

1.0

2.0

Io [mA]

安定領域

0.02

0.05

0.2

5.0

不安定領域

10.0

(3) 7.3 W

(2) 5.5 W

(1) 2.3 W

*Vcc: Applied voltage

Io1: Load current on Vo1 side

Io2: Load current on Vo2 side

Icc: Circuit current

* The Icc (circuit current) varies with the load.

(See reference data in Figs. 2, 3, 14, and 15.)

Unstable region

Unstable region

Unstable region

Stable region

Stable region

Vo1

Vo2

Controller

3.3 V output

Vcc

GND

Vcc

Vcc

Power Tr

Power Tr

1.5 V output or

1.8 V output

Icc