BD9045FV-E2 Rohm Semiconductor, BD9045FV-E2 Datasheet - Page 8

• Manufacturer Part Number: BD9045FV-E2
• Description: IC REG SW STEP DOWN HE 28SSOP
• Manufacturer: Rohm Semiconductor
• Type: Step-Down (Buck)r

Specifications of BD9045FV-E2

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Frequency - Switching: 200kHz ~ 750kHz
• Voltage - Input: 4.5 ~ 18 V
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Power - Output: 940mW
• Primary Input Voltage: 12V
• No. Of Outputs: 1
• Output Voltage: 5.5V
• Output Current: 6mA
• Voltage Regulator Case Style: SSOP
• No. Of Pins: 28
• Operating Temperature Range: -40°C To +85°C
• Svhc: No SVHC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Output: -
• Operating Temperature: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: BD9045FV-E2TR

(1) Setting of output L constant
(2) Setting of output constant Co
(3) Selection of input capacitor（Cin）
Please select the larger capacitance from between the allowable value of ripple voltage V
change of load, as the value of the capacitor used on the output. The output ripple voltage is determined by the following formula.
● Method to select the application parts
Drop of voltage:
reduced.
Please set in such a way that the ripple voltage is within the allowable one.
voltage can be reduced. Moreover, because it is necessary to set the initial rise time of output within the soft start time, please also take
the conditions of the formula (5) into consideration while determining the capacitance of the output capacitor.
If the capacitance is not the optimum, it is possible to cause bad start-up etc.
Please select such a coil as has a low resistance component in order to reduce the loss in the coil and improve the efficiency.
Please select in such a way that a good margin is left so that the peak current does not exceed the coil’s rated current value.
Please select the rating of capacitor in such a way that a good margin is left for output voltage. If ESR is small, the output ripple
If a current exceeding the rated current value of coil flows in coil, the coil will cause magnetic saturation, and so the efficiency is
VIN
Co ≦
Output ripple current
Input capacitor
VCC
Cin
L
Δ IL
I
Tss × (ILimit – I
L
ΔV
L
PP
= ΔI
V
VOUT
Co
Co
OUT
VOUT
L
× R
OUT
ESR
)
+
・・・ （5）
ΔI
ΔIL =
The value of coil has a great influence on output ripple current. As shown in the formula (1),
the bigger the coil, and the higher the switching frequency, the more the ripple current is
reduced.
The appropriate set value of output ripple current is about 30% of maximum output current.
ΔIL = 0.3×IOUTmax.[A]・・・ （2）
（ΔIL：output ripple current, f：switching frequency）
on input terminal (VCC). If this power supply’s output impedance increases, the input
It is necessary to select the input capacitor with low ESR and small capacitance change
caused by temperature change so as to make full preparation for big ripple current. The
ripple current IRMS is determined by the formula (Io).
Moreover, it is greatly dependant on the characteristics of the power supply used on input,
the wiring pattern of board and the gate – drain capacitance of MOSFET, so please fully
confirm the service temperature, load range and MOSFET’s conditions.
Co
Input capacitor plays a role in reducing the output impedance of the power supp connected
L =
L
voltage (VCC) becomes unstable, and the deterioration of oscillation or ripple rejection
characteristics may be caused. Therefore, please be sure to put it near VCC and GND
terminals.
IRMS = IOUT ×
×
（VCC-VOUT）×VOUT
（VCC-VOUT）×VOUT
Vcc
Vo
ΔIL×VCC×f
L×VCC×f
8/16
×
1
f
Tss：soft start time
I
V
ILimit：detected value of overcurrent Refer to
OUT
OUT
[V]･･･(4)
VOUT（VCC - VOUT）
：load current
：output voltage
[A]・・・ （1）
PP
[H]・・・ （3）
VCC
and the allowable value of drop voltage at a sudden
provided that f： switching frequency
[A]・・・ （6）