BD9870FPS-E2 Rohm Semiconductor, BD9870FPS-E2 Datasheet - Page 5

• Manufacturer Part Number: BD9870FPS-E2
• Description: IC REG SW STEP DOWN TO-252S-5
• Manufacturer: Rohm Semiconductor
• Type: Step-Down (Buck)r

Specifications of BD9870FPS-E2

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Current - Output: 1.5A
• Frequency - Switching: 900kHz
• Voltage - Input: 8 ~ 35 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: DPak, TO-252 (Slim, 4 leads + tab)
• Power - Output: 800mW
• Input Voltage: 36 V
• Switching Frequency: 900 KHz
• Operating Temperature Range: -40 C to +85 C
• 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: BD9870FPS-E2TR

●Application component selection and settings
BD9870FPS
© 2009 ROHM Co., Ltd. All rights reserved.
www.rohm.com
Inductor L1
Schottky Diode D1
Output Capacitor C1
Input Capacitor C2
Capacitor C3
Resistor R1,R2
insufficient and oscillation is likely, connecting this capacitor may improve frequency stability.
A large inductor series impedance will result in deterioration of efficiency. OCP operation greater than 1.6A may cause
inductor overheating, possibly leading to overload or output short.
Note that the current rating for the coil should be higher than I
Iout（MAX）: maximum load current
If you flow more than maximum current rating, coil will become overload, and cause magnetic saturation, and those
account for
efficiency deterioration. Select from enough current rating of coil which doesn’t over peak current.
L1：inductor value, VCC：maximum input voltage, VOUT：output voltage,
⊿IL：coil ripple current value, fosc：oscillation frequency
If you make a point of efficiency, we will recommend C10-H5R(mitsumi).The efficiency will improve about 1-2%.
A Schottky diode with extremely low forward voltage should be used. Selection should be based on the following
guidelines regarding maximum forward current, reverse voltage, and power dissipation:
・The maximum current rating is higher than the combined maximum load current and coil ripple current (⊿I
・The reverse voltage rating is higher than the VIN value.
・Power dissipation for the selected diode must be within the rated level.
The power dissipation of the diode is expressed by the following formula:
Pdi=Iout(MAX)×Vf×(1-VOUT/VCC)
Iout（MAX）: maximum load current, Vf: forward voltage, VOUT: output voltage, VCC: input voltage
A suitable output capacitor should satisfy the following formula for ESR:
ESR≦⊿VL/⊿IL
⊿VL : permissible ripple voltage, ⊿IL : coil ripple current
Another factor that must be considered is the permissible ripple current. Select a capacitor with sufficient margin, governed
by the following formula:
IRMS =⊿IL/2√3
IRMS: effective value of ripple current to the output capacitor, ⊿IL : coil ripple current
Use ceramic capacitor over B characteristic of temperature. Except that, it is possible to cause abnormal movement of IC.
It’s depends on ambient temperature or output voltage setting
Also it is possible to use Al electronic capacitor, but use it by enough confirmation.
The input capacitor is the source of current flow to the coil via the built-in Pch FET when the FET is ON. When selecting
the input capacitor sufficient margin must be provided to accommodate capacitor voltage and permissible ripple current.
The expression below defines the effective value of the ripple current to the input capacitor. It should be used in
determining the suitability of the capacitor in providing sufficient margin for the permissible ripple current.
These resistors determine the output voltage:
Select resistors less than 10kΩ.
This capacitor is utilized to stabilize the frequency characteristics, but is seldom used. However, if the phase margin is
⊿IL
VOUT＝1.0V×(1 + R1/R2)
IRMS : effective value of the ripple current to the input capacitor
IOUT : output load current, VOUT: output voltage, VCC: input voltage
.
IRMS＝IOUT×√ (1－VOUT / VCC)×VOUT / VCC
=
(VCC－VOUT)
L1
×
VOUT
VCC
×
fosc
1
5/11
OUT
(MAX)＋⊿IL
.
Technical Note
2009.05 - Rev.A
L
).