BD9859EFJ Datasheet, PDF(4/16 Page) Rohm – Simple Step-down Switching Regulators with Built-in Power MOSFET

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BD9859EFJ Datasheet, PDF (4/16 Pages) Rohm – Simple Step-down Switching Regulators with Built-in Power MOSFET

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BD9859EFJ

Technical Note

âBlock Description

1. Reference

This Block generates Error Amp Standard Voltage.

Standard Voltage is 1.0V.

2. REG

This is a Gate Drive Voltage Generator and 5VLow Saturation regulator for internal Circuit Power supply.

3. OSC

This is a precise wave Oscillation Circuit with Operation Frequency fixed to 750kHz fixed.

4. Soft Start

A Circuit that does Soft Start to the Output Voltage of DCï¼DC Comparator, and prevents Rush Current during

Start-up. Soft Start Time is set at IC internal, after 4mSecs from starting-up EN Pin, Standard Voltage comes to 1.0V,

and Output Voltage becomes set Voltage.

5. ERROR AMP

This is an Error amplifier what detects Output Signal, and outputs PWM Control Signal.

Internal Standard Voltage is set to 1.0V.

Also, C and R are connected between the Output (VC) Pin GND of Error Amp as Phase compensation elements.

(See Page11)

6. ICOMP

This is a Voltage-Pulse Width Converter that controls Output Voltage in response to Input Voltage.

This compares the Voltage added to the internal SLOPE waveform in response to the FET WS Current with Error

amplifier Output Voltage, controls the width of Output Pulse and outputs to Driver.

7. Nch FET SW

This is an internal commutation SW that converts Coil Current of DC/DC Comparator.

It contains 15Vâwithstand pressureâ 100mâ¦SW.

Because the Current Rating of this FET is 3.0A, including Ripple Current of DC Current+Coil, please use at within

3.0A

8. UVLO

This is a Low Voltage Error Prevention Circuit.

This prevents internal circuit error during increase of Power supply Voltage and during decline of Power supply

Voltage.

It monitors VCC Pin Voltage and internal REG VoltageãAnd when VCC Voltage becomes 4.4V and below, it turns

OFF all Output FET and turns OFF DCï¼DC Comparator Output, and Soft Start Circuit resets.

Now this Threshold has Hysteresis of 200mV.

9. TSD

This is a Heat Protect (Temperature Protect) Circuit.

When it detects an abnormal temperature exceeding Maximum Junction Temperature (Tj=150â), it turns OFF all

Output FET, and turns OFF DC/DC Comparator Output. When Temperature falls, it has/with Hysteresis and

automatically returns.

10. EN

With the Voltage applied to EN Pin(5pin), IC ONï¼OFF can be controlled.

When a Voltage of 2.0V or more is applied, it turns ON, at Open or 0V application, it turns OFF.

About 400kâ¦ Pull-down Resistance is contained within the Pin.

www.rohm.com

4/15

2010.02 - Rev.A

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