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BM0123A 데이터시트 PDF




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부품번호 BM0123A 기능
기능 Inherently Matched LED Current driver chip
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BM0123A 데이터시트, 핀배열, 회로
BOOKLY
Features
z Inherently Matched LED Current driver chip
z High Efficiency:83%
z Drives Up to Five LEDs from 2.2V Supply
z 17V Over Voltage Protection
z Fast 1.4MHz Switching Frequency
z Requires Only 1μF Output Capacitors
z SOT-23-6 Package
BM0123A
Applications
z Communication equipment
z White LED Backlight Display for PDA
z Pocket PC
z Handheld Devices
z GPS, portable DVD, digital-frame
z White LED display backlighting
General Description
The BM0123A is a step-up DC/DC converter specifically designed to drive up to 5
series white LEDs with constant current. Series connection of the LEDs provides identical
LED currents resulting in uniform brightness and eliminates the need for ballast resistors.
The BM0123A switches at 1.4MHz, allowing the use of tiny external components. A low
0.255V feedback voltage minimizes power loss in the current setting resistor for high
efficiency. The OVP pin monitors the output voltage and turns off the converter whenever
the LEDs are open. The BM0123A is available in low profile SOT-23-6 package.
It can drive up to 5 (series) * 9 (parallel) LEDs
Pin to pin with RT9271 and AIC1896
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BM0123A pdf, 반도체, 판매, 대치품
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BM0123A
Function Description
The BM0123A uses a constant frequency control scheme to provide excellent line
and load regulation. Operation can be best understood by referring to the block diagram.
At the start of each oscillator cycle, the SR latch is set, which turns on the power switch
M1. An artificial ramp is generated to the positive terminal of the PWM comparator A2.
When this voltage exceeds the level at the negative input of A2, the SR latch is reset
turning off the power switch. The level at the negative input of A2 is set by the error
amplifier A1, and is simply an amplified version of the difference between the feedback
voltage and the reference voltage of 0.254V. In this manner, the error amplifier sets the
correct peak current level to keep the output in regulation. If the error amplifier’s output
increases, more current is delivered to the output, if it decreases, less current is delivered.
Shutdown
The shutdown pin, SHDN, must not be allowed to float. When the SHDN pin voltage is
taken below 0.8V, the internal MOSFET, voltage reference, error amplifier, comparators
and biasing circuitry will all be switched off reducing the quiescent supply current to less
than 1_A. If the SHDN pin has a value greater
than 1.3V, then the device will be fully enabled and operational. This pin also can be used
as a PWM signal from 100Hz to 1kHz to allow brightness control.
Over Voltage Protection
The OVP function is designed to prevent damage to the internal NMOS switching
transistor. When the output voltage rises above the OVP threshold voltage, typically 17V,
the converter will clamp the output voltage to this level. When the output voltage returns to
a value below the OVP threshold, it will automatically resume normal switching operation.
Application Information
Inductor Selection
A 10μH inductor is recommended for BM0123A applications. Small size and high
efficiency are the major concerns for most BM0123A applications. Inductor with low core
losses and small DCR (cooper wire resistance) at 1.4MHz are good choice for BM0123A
applications.
Diode Selection
Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the
ideal choices for BM0123A applications. The forward voltage drop of a Schottky diode
represents the conduction losses in the diode, while the diode capacitance (CT or CD)
represents the switching losses. For diode selection, both forward voltage drop and diode
capacitance need to be considered. Schottky diodes with higher current ratings usually
have lower forward voltage drop and larger diode capacitance, which can cause
significant switching losses at the 1.4MHz switching frequency of the BM0123A. A
Schottky diode rated at 500mA is sufficient for most BM0123A applications.
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관련 데이터시트

부품번호상세설명 및 기능제조사
BM0123A

Inherently Matched LED Current driver chip

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