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PDF BL8501 Data sheet ( Hoja de datos )
| Número de pieza | BL8501 | |
| Descripción | Step down DC/DC controller | |
| Fabricantes | SHANGHAI BELLING | |
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BL8501
Step down DC/DC controller
OUTLINE
The BL8501 is a CMOS-based PWM step-down DC-DC Converter controller. The device can
offer the following advantages: lower supply current and wider operating input-voltage range.
The BL8501 consists of an oscillator, a PWM control circuit, a reference voltage unit, an error
amplifier, a soft-start circuit, a protection circuit, a PWM/VFM alternative circuit, a chip enable
circuit, and detecting input voltage circuit. A low ripple, high efficiency step-down DC-DC
converter can be easily composed of this IC with only several external components, or a
power-transistor, an inductor, a diode and capacitors. Output Voltage can be adjusted with
external resistors.
FEATURES
Range of input Voltage: 3.5V~12V
Built-in Soft-start Function and Protection Function (Reset type protection)
Oscillation Frequency: 500KHz
High efficiency: 90%
High Accuracy Output Voltage: 2.0%
Low Temperature-Drift Coefficient of Output Voltage: Typ: 100ppm/°C
Operating Temperature Range: -20 ~85
APPLICATIONS
Power source for hand-held communication equipment, cameras, video instruments
such as VCRs, camcorders.
Power source for battery-powered equipment.
Power source for household electrical appliances.
PIN CONFIGURATION
SOT-23-5L
PIN DESCRIPTION
Pin No.
Symbol
1 CE
2 GND
3 VFB
4 EXT
5 VIN
Description
Chip Enable Pin (Active with “H”)
Ground Pin
Pin for Feedback Voltage
External Transistor Drive Pin (CMOS Output)
Power Supply Pin
DETAILED DESCRIPTION
http://www.belling.com.cn
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8/8/2006
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BL8501
frequency characteristics such as tantalum capacitors. We recommend you to use output
capacitors with an allowable voltage at least twice as much as setting output voltage. This is
because there may be a case where a spike –shaped high voltage is generated by an
inductor when an external transistor is on and off.
Choose an inductor that has sufficiently small D.C. resistance and large allowable current
and is hard to reach magnetic saturation. And if the value of inductance of an inductor is
extremely small, the I LX may exceed the absolute maximum rating at the maximum
loading.
Use an inductor with appropriate inductance.
Use a diode of a Schottky type with high switching speed, and also pay attention to its
current capacity.
Do not use this IC under the condition with VIN voltage at equal or less than minimum
operating voltage.
When the threshold level of an external power MOSFET is rather low and the drive-ability of
voltage supplier is small, if the output pin is short circuit, input voltage may be equal or less
than UVLO detector threshold. In this case, the device is reset with UVLO function that is
different from the reset-protection function caused by maximum duty cycle.
With the PWM/VFM alternative circuit, when the on duty cycle of switching is 20% or less,
the IC alters from PWM mode to VFM mode (Pulse skip mode). The purpose of this circuit is
raising the efficiency with a light load by skipping the frequency and suppressing the
consumption current. However, the ratio of output voltage against input voltage is 20% or
less, (ex. VIN >10V and VOUT =2V) even if the large current may be loaded, the IC keeps its
VFM mode. As a result, frequency might be decreased, and oscillation waveform might be
unstable. These phenomena are the typical characteristics of the IC with PWM/VFM
alternative circuit.
The performance of power source circuits using this IC extremely depends upon the
peripheral circuits. Pay attention in the selection of the peripheral circuits. In particular, design
the peripheral circuits in a way that the values such as voltage, current, and power of each
component, PCB patterns and the IC does not exceed their respected rated values.
How to Adjust Output Voltage and about Phase Compensation
As for adjustable Output type, feedback pin (VFB ) voltage is controlled to maintain 1.0V.
Output Voltage, VOUT is as following equation:
VOUT : (R2+R4)=VFB : R2
VOUT =VFB *(R2+R4)/R2
http://www.belling.com.cn
- 5-
Total 10 Pages
8/8/2006
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet BL8501.PDF ] | |
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