BA3259HFP_09 ROHM [Rohm], BA3259HFP_09 Datasheet - Page 6

• Manufacturer Part Number: BA3259HFP_09
• Description: Dual-output Secondary Fixed/Variable Output LDO Regulators for Local Power Supplies
• Manufacturer: ROHM [Rohm]

Function Explanation
Thermal Design
© 2009 ROHM Co., Ltd. All rights reserved.
5V
BA3259HFP,BA30E00WHFP
www.rohm.com
Fig. 27 Ambient Temperature vs. Power Dissipation
Conventional
10
6
9
8
7
5
4
3
2
1
0
Vcc
AMBIENT TEMPERATURE: Ta [°C]
1) Two-input power supply (BA30E00WHFP)
2) Standby function (BA30E00WHFP)
If the IC is used under the conditions of excess of the power dissipation, 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 exceeds T
the power 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. 27.
Power Consumption Pc (W) Calculation Method:
BA3259HFP
The Icc (circuit current) varies with the load.
Refer
excess power dissipation Pd under all operating temperatures.
(1) 2.3W
(2) 5.5W
(3) 7.3W
0
Vcc
The input voltages (Vcc1 and Vcc2) supply power to two outputs (Vo1 and Vo2, respectively). The power dissipation
between the input and output pins can be suppressed for each output according to usage.
Efficiency comparison:
5V single input vs. 5V/3V two inputs
Regulator with single input and two outputs
The standby function is operated through the EN pin. Output is turned on at 2.0 V or higher and turned off at 0.8 V or lower.
25
REG1
to the above and implement proper thermal designs so that the IC will not be used under conditions of
REG2
Controller
I
P
50
Board size: 70 mm  70 mm  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  15 mm)
(2) 2-layer board (Backside copper foil area: 70 mm  70 mm)
(3) 4-layer board (Backside copper foil area: 70 mm  70 mm)
Vo2
GND
Vo1
Icc
75
1.8 V/0.3 A
3.3 V/0.3 A
Power
Power
100 125 150
Tr
Tr
Vcc
Vcc
jmax
Power loss between input and output
= (5 − 3.3)  0.3 + (5 − 1.8)  0.3
= 0.51W + 0.96W
= 1.47W
 Single 5V input results in decreased
efficiency
Vo1
Vo2
, element deterioration or damage may occur. Implement proper thermal designs to ensure that
(Vcc − Vo1)  Io1 + (Vcc − Vo2)  Io2
3.3 V
output
Io1
0.8 V to
3.3 V
output
Io2
 Power consumption of 3.3 V power
 Power consumption of Vo2 power
 Power consumption by circuit current
* Vcc: Applied voltage
transistor
transistor
Io1: Load current on Vo1 side
Io2: Load current on Vo2 side
Icc: Circuit current
Pc1=(Vcc − 3.3)  Io1
Pc2=(Vcc − Vo2)  Io2
Pc3=Vcc  Icc
Pc=Pc1 + Pc2 + Pc3

10.0
0.05
0.02
0.01
2.0
1.0
0.5
0.2
0.1
5.0
0
Fig.28 BA3259HFP ESR
Regulator with two inputs and two outputs
200
6/9
(Vo2=1.8V, Io1=Io2=0.3A)
Unstable region
Stable region
5V
Vcc1
3V
BA30E00WHFP
Vcc2
Current
400
Io [mA]
Vcc
600
Controller
REG1
REG2
GND
800 1000
Icc1+Icc2
Vo2
Vo1
I
I
B
B
1
2
Power
Power
1.8 V/0.3 A
3.3 V/0.3 A
Tr
Tr
Vcc1
Vcc2
10.0
0.05
0.02
0.01
2.0
1.0
0.7
0.5
0.2
0.1
5.0
Io1
Io2
0
3.3 V
output
Io1
0.8 V to
3.3 V
output
Io2
Fig.29 BA30E00WHFP ESR
Power loss between input and output
= (5 − 3.3)  0.3 + (5 − 1.8)  0.3
= 0.51W + 0.36W
= 0.87W
 Additional 3V input improves efficiency
(Vcc1 − Vo1)  Io1 + (Vcc2 − Vo2)  Io2
200
 Power consumption of power transistor on
 Power consumption of power transistor on
 Power consumption by circuit current
* Vcc1, Vcc2: Applied voltage
Vol1 (3.3 V output)
Vo2 (variable output )
Io1: Load current on 3.3 V output side
Io2: Load current on variable output side
Icc1, Icc2:
Pc1=(Vcc1 − Vo1)  Io1
Pc2=(Vcc2 − Vo2)  Io2
Pc3=Vcc1  Icc1 + Vcc2  Icc2
Pc=Pc1 + Pc2 + Pc3
Stable region
Unstable region
Unstable region
400
2009.04 - Rev.A
Technical Note
Io [mA]

Reduced power loss by
0.6W.
Circuit currents
600
800 1000