오늘은 DCDC Converter인 EMP3484에 대한 고찰을 해 보겠습니다.
EMP3484은 출력 3A용, Buck Converter로서 아래와 같은 특성을 지니고 있습니다.
특히 내부에 Feedback의 Compensation(보상) 회로가 들어있어 외부 소자, 즉 주변회로가 간단합니다.
입력 전압은 4.5V to 30V로 Wide range입니다.
General Description
The EMP3484 is a high frequency, synchronous, rectified, step- down, switch-mode converter with internal power MOSFETs.
It offers a very compact solution to provide a 3A continuous current over a wide input supply range with excellent load and line regulation.
The EMP3484 requires a minimal number of readily available, external components and is available in
a space saving ESOP8 package.
Features and Benefits
Wide 4.5V to 30V Operating Input Range
3A Continuous Output Current
500KHz Switching Frequency
Short Protection with Hiccup-Mode
Built-in Over Current Limit
Built-in Over Voltage Protection
PFM Mode for High Efficiency in Light Load
Internal Soft-Start
130mΩ/100mΩ Low RDS(ON) Internal Power MOSFETs
Output Adjustable from 0.923V
No Schottky Diode Required
Integrated internal compensation
Thermal Shutdown
Available in ESOP8 Package
-40°C to +85°C Temperature Range
Applications
Digital Set-top Box (STB)
Tablet Personal Computer (Pad)
Flat-Panel Television and Monitor
Wi-Fi Router / AP
Digital Video Recorder (DVR)
Portable Media Player (PMP)
Cable Modem / XDSL
General Purposes
Functions Description.
Internal Regulator
The EMP3484 is a current mode step down DC/DC converter that provides excellent transient response
with no extra external compensation components.
This device contains an internal, low resistance, high voltage power MOSFET,
and operates at a high 500KHz operating frequency to ensure a compact,
high efficiency design with excellent AC and DC performance.
Error Amplifie
The error amplifier compares the FB pin voltage with the internal FB reference (VFB) and outputs a
current proportional to the difference between the two.
This output current is then used to charge or discharge the internal compensation network,
which is used to control the power MOSFET current.
The optimized internal compensation network minimizes the external component counts and simplifies the
control loop design
Under-Voltage Lockout (UVLO)
Under-voltage lockout (UVLO) protects the chip from operating at an insufficient supply voltage.
UVLO protection monitors the internal regulator voltage.
When the voltage is lower than UVLO threshold voltage, the device is shut off.
When the voltage is higher than UVLO threshold voltage, the device is enabled again.
Thermal Shutdown
Thermal shutdown prevents the chip from operating at exceedingly high temperatures.
When the silicon die temperature exceeds 160°C, it shuts down the whole chip.
When the temperature falls below its lower threshold (Typ. 130°C) the chip is enabled again.
Internal Soft-Start
The soft-start is implemented to prevent the converter output voltage from overshooting during startup.
When the chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 0.923V.
When it is lower than the internal reference (REF), SS overrides REF so the error amplifier uses SS as the reference.
When SS is higher than REF, REF regains control. The SS time is internally max to 1ms.
Over Current Protection and Hiccup
The EMP3484 has cycle-by-cycle over current limit when the inductor current peak value exceeds the
set current limit threshold.
Meanwhile, output voltage starts to drop until FB is below the Under-Voltage (UV) threshold.
Once a UV is triggered, the EMP3484 enters hiccup mode to periodically restart the part.
This protection mode is especially useful when the output is dead-short to ground.
The average short circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator.
The EMP3484 exits the hiccup mode once the over current condition is removed.
Startup and Shutdown
If both VIN and EN are higher than their appropriate thresholds, the chip starts.
The reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled.
The regulator provides stable supply for the remaining circuitries.
Three events can shut down the chip: EN low, VIN low and thermal shutdown.
In the shutdown procedure, the signaling path is first blocked to avoid any fault triggering.
The comp voltage and the internal supply rail are then pulled down.
The floating driver is not subject to this shutdown command.
PC Board Layout Consideration
PCB layout is very important to achieve stable operation.
It is highly recommended to duplicate EVB layout for optimum performance.
If change is necessary, please follow these guidelines for reference.
1. Keep the path of switching current short and minimize the loop area formed by Input capacitor,
high-side MOSFET and low-side MOSFET.
2. Bypass ceramic capacitors are suggested to be put close to the VIN Pin.
3. Ensure all feedback connections are short and direct.
Place the feedback resistors and compensation components as close to the chip as possible.
4. VOUT, SW away from sensitive analog areas such as FB.
5. Connect IN, SW, and especially GND respectively to a large copper area to cool the chip to
improve thermal performance and long-term reliability.
아래는 spec sheet입니다.
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