BD9673EFJ-E2 ROHM Electronics, BD9673EFJ-E2 Datasheet - Page 12

• Manufacturer Part Number: BD9673EFJ-E2
• Description: Specifications: Type: Step-Down (Buck) ; Output Type: Adjustable ; PWM Type: Current Mode ; Synchronous Rectifier: Yes ; Number of Outputs: 1 ; Voltage - Output: 1 V ~ 29.4 V ; Current - Output: 1.5A ; Frequency - Switching: 300kHz ; Voltage - Input:
• Manufacturer: ROHM Electronics

●Application Components Selection Method
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BD9673EFJ
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(1) Inductor
(2) Output Capacitor
(3) Output Voltage Setting
(4) Boost Capacitor
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.
(η:Efficiency, ⊿IL:Output Ripple Current, f:Switching Frequency )
For design value of Inductor Ripple Current, please carry out design tentatively with about 20％～50% of Maximum
Input Current.
※When current that exceeds Coil rating flows to the coil, the Coil causes a Magnetic Saturation, and there are cases
In order for Capacitor to be used in Output to reduce Output Ripple, Low Ceramic Capacitor of ESR is recommended.
Also, for Capacitor Rating, on top of putting into consideration DC Bias Characteristics, please use something whose
Maximum Rating has sufficient margin with respect to the Output Voltage.
Output Ripple Voltage is looked for using the following formula.
Please design in a way that it is held within Capacity Ripple Voltage.
ERROR AMP internal Standard Voltage is 1.0V. Output Voltage is determined as seen in (4) formula.
Please connect CBST=0.01µF (Laminate Ceramic Capacitor) between BST Pin-Lx Pins as Output capacitors of Gate
Drive Voltage Generator REG (5V).
Vpp=⊿IL×
⊿IL=
Ipeak =Iout + ⊿IL/2 [A]
wherein a decline in efficiency, oscillation of output happens. Please have sufficient margin and select so that Peak
Current does not exceed Rating Current of Coil.
Vin-Vout
L
2π×f×Co
R1
R2
VOUT
1
×
FB
+ ⊿IL×R
Vout
Vin
Fig.32 Voltage Return Resistance Setting Method
1.0V
VREF
ERROR AMP
×
ESR
1
f
[A]
[V] ・・・ (3)
12/18
Vo=
(R1+R2)
(2)
(1)
R2
×1.0 [V] ・・・ (4)
Fig.31 Inductor Current
ΔI
L
Technical Note
2012.02 - Rev.C