FP5217-Non-Synchronous PWM Boost Converter (MOSFET: 30V/8A/15mΩ -peak current 10A)에 대한 고찰

 

 

 

오늘은 FP5217-Non-Synchronous PWM Boost Converter (MOSFET: 30V/8A/15mΩ -peak current 10A)에 대한 고찰을 해 보겠습니다.

FP5217은 Non-Synchronous PWM Boost Converter로 아래와 같은 특성을 지니고 있습니다.

 

The FP5217 is boost topology switching regulator for wide operating voltage applications. Its built-in 15mΩ power MOSFET makes this regulator highly power efficient. The non-inverting input of error amplifier connects to a 1.2V precision reference voltage. It has programmable switching frequency set by external resistor, and programmable inductor peak current limit connects a resistor from CS to GND. Current mode control and external compensation network make is easy and flexible to stabilize the system.
The FP5217 is available in the small footprint TSSOP-14L(EP) package to fit in space-saving PCB layout for application fields.

 

• Start-up Voltage: 2.8V

• Wide Supply Voltage Operating Range: 5V to 24V

• Adjustable Output up to 26V

• Precision Feedback Reference Voltage: 1.2V (±2%)

• Shutdown Current: <3μA

• Programmable Switching Frequency: 200KHz~1000KHz

• Programmable Soft Start Function (SS)

• Input Under Voltage Protection (UVP)

• Adjustable Switching MOSFET Over Current Protection (OCP)

• Over Temperature Protection (OTP)

• MOSFET: 30V/8A/15mΩ (peak current 10A)

• Package: TSSOP-14L(EP)

 

 

Function Description

Operation
The FP5217 is current mode boost converter. It operates with pulse width modulation (PWM).
The internal resistive divider provides 1.2V reference for the error amplifier. 

It changes to PSM mode when the output is light load. 

In PSM mode, it can reduce switching lose to raise efficiency, but the output ripple is bigger.

 

Soft Start Function
Soft start time is programmable to connect capacitor between SS pin to ground. 

After the IC is enabled, the output of error amplifier is clamped by the internal soft-start function, 

which causes PWM pulse width increasing slowly and thus reducing input surge current during power on. 

The soft start bias current is 3.5μA.

 

Oscillator
The oscillator frequency can be set from 200KHz to 1000KHz by external resistance. 

Acceptable resistance values range from 100KΩ to 17KΩ. 

The RT pin can’t float must connect a resistance to ground.

 

 

Enable Mode / Shutdown Mode
Input voltage connects to EN pin through a resistive divider to set UVLO threshold. FP5217 is
enabled when EN voltage greater than 1.5V. The EN voltage is lower than 1.3V to shutdown it. 

In shutdown mode, to turn off circuitry includes SW signal, VDS voltage, and supply current of HVDD
reduces less than 3μA.

The EN hysteresis voltage is 0.2V. HVDD voltage may be lower than 5V, it can’t use a resistive divider to set UVLO threshold. 

For instance, input voltage is from 3V to 4.2V, HVDD pin connects to output 12V, when UVLO is triggered to shutdown FP5217, 

HVDD and output are approximately input voltage. 

If the applications don’t need to set UVLO, the EN connects to input voltage through resistance 200KΩ.

 

Current Sense Control
Internal switching MOSFET is turned on inductor current flows across the current sense resistor to
generate VCS. VCS provides part of current mode control loop. 

Internal leading-edge blanking is provided to prevent premature turn off the switching MOSFET in each switching cycle.

 

Current Limit Setting Resistor (RCS)

RCS is connected between SWS and ground, and then CS connects to RCS through R13.

 

Thermal Shutdown Protection
The IC will shutdown automatically when the internal junction temperature exceeds +150°C. 

The device can restart until the junction temperature drops below +120°C approximately.

 

 

Application Information

Inductor Selection
The Inductance value is decided based on different condition. 3.3μH to 47uH inductance value is
recommended for general application circuit. 

There are three important inductor specifications, DC resistance, saturation current and core loss. 

Low DC resistance has better power efficiency.

 

 

Capacitor Selection
Output capacitor is required to maintain the DC voltage during switching. 

Low ESR capacitors are preferred to reduce the output voltage ripple. 

Ceramic capacitor of X5R and X7R are recommended, which have low equivalent series resistance (ESR) 

and wider operation temperature range.

 

Diode Selection
Schottky diodes with fast recovery times and low forward voltages are recommended. 

Ensure the diode average and peak current rating exceed the average output current and peak inductor current. 

In addition, the diode’s reverse breakdown voltage must exceed the output voltage.

 

Output Voltage Programming
The output voltage is set by a resistive voltage divider from the output voltage to FB.

 

 

 

아래 Demo Board는 Vin=10V, VAout=15V/2A, Switching Frequency=417kHz 정도로 spec을 정해서 application 하면,

• Efficiency=94.9%

• Output Ripple=250mV

• 각 부품의 Temperature IC1=58℃, L1=63℃, D1=69℃입니다.

 

 

아래는 spec sheet에 있는 응용회로입니다.

 

응용회로

 

 

아래는 PCB Artwork시에 부품 및 Pattern Layout을 고려해야하는부분입니다.

 

1. The power traces, consisting of the GND trace, the SWD pin trace and the VIN trace should be kept short, direct and wide.

2. Layout switching node SWD pin, inductor and schottky diode connection traces wide and short to reduce EMI.

3. Place C6 nearby HVDD pin as closely as possible to maintain input voltage steady and filter noise.

4. Resistive divider R11 and R12 must be connected to FB and GND pin directly and as closely as possible.

5. FB is a sensitive node. Please keep it away from switching node, SWD pin.

6. The GND of the RCS, C1, C6, C7 and C8 should be connected close and together directly to a ground plane.

7. RCS must be connected to CS and GND pin directly and as closely as possible.

8. The output capacitor C7 and C8 should be connected close and together directly to the ground of RCS.

9. The X5R and X7R of ceramic capacitors are recommended to choose.

10. R9 and C9 are added for reducing EMI (Electromagnetic Interference).

 

 

FP5217V061-G1.pdf

0.60MB