BD8381EFV-E2 Rohm Semiconductor, BD8381EFV-E2 Datasheet - Page 14

• Manufacturer Part Number: BD8381EFV-E2
• Description: LED Drivers AUTOMOTIVE GRADE LED DRIVER
• Manufacturer: Rohm Semiconductor

Specifications of BD8381EFV-E2

• Operating Supply Voltage: 5 V to 30 V
• Maximum Supply Current: 7 mA
• Maximum Power Dissipation: 1.45 W
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: HTSSOP-28
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

5.
6.
© 2010 ROHM Co., Ltd. All rights reserved.
BD8381EFV-M
7. Phase Compensation Guidelines
www.rohm.com
In general, the negative feedback loop is stable when the following condition is met:
However, as the DC/DC converter constantly samples the switching frequency, the gain-bandwidth (GBW) product of the entire series
should be set to 1/10 the switching frequency of the system. Therefore, the overall stability characteristics of the application are as follows:
Thus, to improve response within the GBW product limits, the switching frequency must be increased.
A capacitor at the input is also required as the peak current flows between the input and the output in DC/DC conversion.
We recommend an input capacitor greater than 10µF with the ESR smaller than 100mΩ. The input capacitor outside of our
recommendation may cause large ripple voltage at the input and hence lead to malfunction.
The key for achieving stability is to place fz near to the GBW. GBW is decided by phase delay fp1 by COUT and output impedance RL.
Of each becomes like the next expression.
Good stability would be obtained when the fz is set between 1kHz～10kHz.
Please substitute the value at the maximum load for RL.
In buck-boost applications, Right-Hand-Plane (RHP) Zero exists. This Zero has no gain but a pole characteristic in terms of
phase. As this Zero would cause instability when it is in the control loop, so it is necessary to bring this zero before the
GBW.
fRHP=
stability in the actual circuitry. It is also important to note that stability characteristics can change greatly depending on
factors such as substrate layout and load conditions. Therefore, when designing for mass-production, stability should be
thoroughly investigated and confirmed in the actual physical design.
Select the output capacitor Cout based on the requirement of the ripple voltage Vpp.
It is important to keep in mind that these are very loose guidelines, and adjustments may have to be made to ensure
Choose Cout that allows the Vpp to settle within the requirement. Allow some margin also, such as the tolerance of the
external components.
Selection of the output capacitor
Selection of the input capacitor
• Overall gain of 1 (0dB) with a phase lag of less than 150º (i.e., a phase margin of 30º or more)
• Overall gain of 1 (0dB) with a phase lag of less than 150º (i.e., a phase margin of 30º or more)
• GBW (frequency at gain 0dB) of 1/10 the switching frequency
Vpp =
Vout+VIN/(Vout+VIN)
Phase-lead fz =
Phase-lag fp1 =
2π I
Cout
LOAD
Iout
L
×
Vout+V
2π RLCout
2π CpcRpc
Vout
[Hz]
1
1
IN
×
[Hz]
[Hz]
Fosc
I
LOAD
1
: M
+ I
AXIMUM
L_MIN
14/20
× R
L
OAD
ESR
C
URRENT
V
out
LED
FB
A
2010.10 - Rev.0.11
Technical Note
COMP
Rpc
Cpc