BD8381EFV-E2 Rohm Semiconductor, BD8381EFV-E2 Datasheet - Page 6

• 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

● Buck-Boost DC/DC controller
・ Over-voltage protection circuit (OVP)
・ Buck-boost DC/DC converter oscillation frequency (FOSC)
・ External DC/DC converter oscillating frequency synchronization (FSYNC)
・Soft Start Function
© 2010 ROHM Co., Ltd. All rights reserved.
BD8381EFV-M
www.rohm.com
The soft-start (SS) limits the current and slows the rise-time of the output voltage during the start-up, and hence leads to
prevention of the overshoot of the output voltage and the inrush current. The SS voltage is made Low when OVP of the
overcurrent and the excess voltage is detected, and the switching is stopped. Resume operation is begun.
The output of the DCDC converter should be connected to the OVP pin via a voltage divider. In determining an appropriate
trigger voltage of for OVP function, consider the total number of LEDs in series and the maximum variation in VF. Also, bear
in mind that over-current protection (OCP) is triggered at 0.85 x OVP trigger voltage. If the OVP function engages, it will not
release unless the DCDC voltage drops to 72.5% of the OVP trigger voltage. For example, if ROVP1 (out put voltage side),
ROVP2 (GND side), and DCDC voltage VOUT are conditions for OVP, then: VOUT ≥ (ROVP1 + ROVP2) / ROVP2 x 2.0 V.
OVP will engage when VOUT ≧ 32 V if ROVP1 = 330 kΩ and ROVP2 = 22 kΩ.
Do not switch from external to internal oscillation of the DC/DC converter if an external synchronization signal is present on
the SYNC pin. When the signal on the SYNC terminal is switched from high to low, a delay of about 30 µs (typ.) occurs
before the internal oscillation circuitry starts to operate (only the rising edge of the input clock signal on the SYNC terminal is
recognized). Moreover, the external synchronizing signal is given to priority when an external input frequency is used. There
is a possibility of oscillating when the internal oscillation frequency is low, and an external oscillatory frequency is high. Please
set to RT=100kohm when you use an external oscillatory frequency.
The regulator’s internal triangular wave oscillation frequency can be set via a resistor connected to the RT pin (pin 5). This resistor
determines the charge/discharge current to the internal capacitor, thereby changing the oscillating frequency. Refer to the following
theoretical formula when setting RT:
60 x 10
{ RT: α = 50kΩ: 0.98, 60kΩ: 0.985, 70kΩ: 0.99, 80kΩ: 0.994, 90kΩ: 0.996, 100kΩ: 1.0, 150kΩ: 1.01, 200kΩ: 1.02, 300kΩ: 1.03, 400kΩ: 1.04, 500kΩ: 1.045 }
A resistor in the range of 62.6kΩ～523kΩ is recommended. Settings that deviate from the frequency range shown below may cause
switching to stop, and proper operation cannot be guaranteed.
6
(V/A/S) is a constant (±5%) determined by the internal circuitry, and α is a correction factor that varies in relation to RT:
600K
500K
400K
300K
200K
100K
fosc =
0K
0
Fig.13 RT versus switching frequency
60 × 10
200
RT [Ω ]
400
6/20
6
RT [kΩ]
600
x α [kHz]
800
1000
2010.10 - Rev.0.11
Technical Note