BD9673AEFJ Datasheet, PDF (15/23 Pages) Rohm – Flexible Step-down Switching Regulators with Built-in Power MOSFET

BD9673AEFJ
Datasheet
●Power Dissipation
It is shown below reducing characteristics of power dissipation to mount 70mm×70mm×1.6mm^t PCB
Junction temperature must be designed not to exceed 150℃.
4000
④3760mW
3500
3000
HTSOP-J8 Package -
On 70mm×70mm×1.6mm^t glass epoxy PCB
①1-layer board （Backside copper foil area 0mm×0mm）
②2-layer board ( Backside copper foil area 15mm×15mm)
③2-layer board （Backside copper foil area 70mm×70mm）
④4-layer board （Backside copper foil area 70mm×70mm）
2500
2000
③2210mW
1500 ^②1100mW
1000 _①820mW
500
0
0
25
50
75
100
125
150
Ambient Temperature - ℃
Figure 45. Power Dissipation ( 70mm×70mm×1.6mm^t 1layer PCB)
●Power Dissipation Estimate
The following formulas show how to estimate the device power dissipation under continuous mode operations. They should
not be used if the device is working in the discontinuous conduction mode.
The device power dissipation includes:
1) Conduction loss： Pcon = IOUT² × RonH × VOUT/VCC
2) Switching loss: Psw = 1.25 × 10^–9 × VCC² × IOUT × fsw
3) Gate charge loss： Pgc = 22.8 × 10^–9 × fsw
4) Quiescent current loss： Pq = 1.0 × 10^–3 × VCC
Where:
IOUT is the output current (A）, RonH is the on-resistance of the high-side MOSFET（Ω）, VOUT is the output voltage (V).
VCC is the input voltage (V), fsw is the switching frequency (Hz).
Therefore
Power dissipation of IC is the sum of above dissipation.
Pd = Pcon + Psw + Pgc + Pq
For given Tj, Tj =Ta + θja × Pd
Where:
Pd is the total device power dissipation (W), Ta is the ambient temperature (℃)
Tj is the junction temperature (℃), θja is the thermal resistance of the package (℃)
●Application Components Selection Method
(1) Inductor
Something of the shield Type that Fulfills the Current Rating (Current value Ipecac below), with low DCR (Direct Current
Resistance element) is recommended.
Value of Inductor influences Inductor Ripple Current and becomes the cause of Output Ripple.
In the same way as the formula below, this Ripple Current can be made small for as big as the L value of Coil or as high
as the Switching Frequency.
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TSZ22111・15・001
15/20
TSZ02201-0Q1Q0AJ00190-1-2
28.JAN.2014 Rev.003