Technical Note
5/9
BD3570FP/HFP, BD3571FP/HFP, BD3572FP/HFP, BD3573FP/HFP
BD3574FP/HFP, BD3575FP/HFP
www.rohm.com
2011.03 - Rev.B
© 2011 ROHM Co., Ltd. All rights reserved.
●Output Voltage Adjustment
To set the output voltage insert pull-down resistor R1 between the ADJ and GND pins,
and pull-up resistor R2 between the VO and ADJ pins.
Vo = VADJ×(R1+R2) / R1 [V]
｛VADJ=1.26V(TYP.)｝
The recommended connection resistor for the ADJ-GND is 30k～150kΩ.
●Setting of Heat
TO252-3 TO252-5 HRP5
Fig. 23 Fig. 24 Fig. 25
Refer to the heat mitigation characteristics illustrated in Figs. 23, 24 and 25 when using the IC in an environment where Ta
≧25℃. The characteristics of the IC are greatly influenced by the operating temperature. If the temperature is in excess of
the maximum junction temperature T
jmax, the elements of the IC may be deteriorated or 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, it is necessary to operate the IC not in excess of the maximum junction
temperature T
jmax. Fig. 23 illustrates the power dissipation/heat mitigation characteristics for the TO252 package. Operate
the IC within the power dissipation Pd. The following method is used to calculate the power consumption P
C (W).
Vcc : Input voltage
PC=(VCC-VO)×IO+VCC×ICC Vo : Output voltage
Power dissipation Pd≦PC Io : Load current
Icc : Total supply current
The load current I
O is obtained to operate the IC within the power dissipation.
(For more information about ICC, see page 12.)
The maximum load current Iomax for the applied voltage VCC can be calculated during the thermal design process.
●Calculation example
Example: BD3571FP V
CC = 12 V and VO = 5 V at Ta = 85℃
I
O≦89mA (ICC=30μA)
Make a thermal calculation in consideration of the above 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 V
O and GND pins are shorted) will be obtained from
the following equation.
Pc=VCC×(ICC+Ishort) Ishort = Short current
V
CC-VO
Io≦
Pd-V
CC×ICC
IO≦
0.624-12×ICC
12-5
θja=104.2℃/W→-9.6mAW/℃
25℃=1.2W→85℃=0.624W
0
0.4
1.2 W
0
0.8
1.2
1.6
2.0
25 50 75 100 125 150
IC mounted on a ROHM standard board
Substrate size: 70 mm 70 mm 1.6 mm
ja = 104.2 (°C/W)
MBIENT TEMPERATURE: Ta [°C]
POWER DISSIPATION: Pd [W]
0
0.4
1.6 W
0
0.8
1.2
1.6
2.0
25 50 75 100 125 150
IC mounted on a ROHM standard board
Substrate size: 70 mm 70 mm 1.6 mm
ja = 78.1 (°C/W)
MBIENT TEMPERATURE: Ta [°C]
POWER DISSIPATION: Pd [W]
0
0.4
1.3W
0
0.8
1.2
1.6
2.0
25 50 75 100 125 150
MBIENT TEMPERATURE: Ta [℃]
POWER DISSIPATION: Pd [W]
IC mounted on a ROHM standard board
Substrate size: 70 mm 70 mm 1.6 mm
ja = 96.2 (°C/W)
Fig.22
ADJ
Vo
R2
R1
