BD9775FV-E2 Rohm Semiconductor, BD9775FV-E2 Datasheet - Page 8

• Manufacturer Part Number: BD9775FV-E2
• Description: IC REG SW STEP DOWN HE 28-SSOP
• Manufacturer: Rohm Semiconductor
• Type: Step-Down (Buck)r

Specifications of BD9775FV-E2

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Current - Output: 400mA
• Frequency - Switching: 100kHz
• Voltage - Input: 6 ~ 30 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Power - Output: 640mW
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: BD9775FV-E2TR

●Application component selection
(1) Setting the output L value
(2) Setting the output capacitor Co value
(3) Input capacitor selection
Select the output capacitor with the highest value for ripple voltage (V
(at rapid load change). The following equation is used to determine the output ripple voltage.
※Use low resistance (DCR, ACR) coils to minimize coil loss and increase efficiency.
※Please allow sufficient output voltage margin in establishing the capacitor rating. Note that low-ESR capacitors enable
※Outputting a current in excess of the coil current rating will cause magnetic saturation of the coil and decrease
efficiency.
Be sure to keep the output Co setting within the allowable ripple voltage range.
Also, to meet the requirement for setting the output startup time parameter within the soft start time range, please factor
in the conditions described in the capacitance equation (9) for output capacitors, below.
Step down ΔV
Co ≦
Note: less than optimal capacitance values may cause problems at startup.
Please establish sufficient margin to ensure that peak current does not exceed the coil current rating.
lower output ripple voltage.
Output ripple current
TSS × (Limit – IOUT)
Fig-17
VCC
Fig-18
VIN
ΔI
Input capacitor
L
PP
I
Fig-19
L
L
VOUT
= ΔI
Cin
L
VOUT
Co
L
× R
Co
ESR
VOUT
+
・・・ （9）
ΔI
Co
L
×
The coil value significantly influences the output ripple current.
Thus, as seen in equation (5), the larger the coil, and the higher
the switching frequency, the lower the drop in ripple current.
The optimal output ripple current setting is 30% of maximum current.
ΔIL = 0.3×IOUTmax.[A]・・・ （6）
The input capacitor serves to lower the output impedance of the power
source connected to the input pin (VCC). Increased power supply output
impedance can cause input voltage (VCC) instability, and may negatively
impact oscillation and ripple rejection characteristics. Therefore, be
certain to establish an input capacitor in close proximity to the VCC and
GND pins. Select a low-ESR capacitor with the required ripple current
capacity and the capability to withstand temperature changes without
wide tolerance fluctuations. The ripple current IRMSS is determined
using equation (10).
Also, be certain to ascertain the operating temperature, load range and
MOSFET conditions for the application in which the capacitor will be used,
since capacitor performance is heavily dependent on the application’s
input power characteristics, substrate wiring and MOSFET gate drain
capacity.
IRMS = IOUT ×
（ΔIL：output ripple current f：switching frequency）
Vcc
Vo
ΔIL =
8/29
L =
×
Tss： soft start time
ILimit：over current detection value（2/16）reference
（VCC-VOUT）×VOUT
1
（VCC-VOUT）×VOUT
f
PP
L×VCC×f
ΔIL×VCC×f
) tolerance and maximum drop voltage
[V]
VOUT（VCC - VOUT）
Note: f：switching frequency
VCC
[A]・・・ （5）
[H]・・・ （7）
[A]・・・ （10）