FP6165-1.5MHz, 3A Synchronous Step-Down Regulator에 대한 고찰

 

 

 

오늘은 FP6165-1.5MHz, 3A Synchronous Step-Down Regulator에 대한 고찰을 해 보겠습니다.

FP6165은 1.5MHz, 3A Synchronous Step-Down Regulator로 아래와 같은 특성을 지니고 있습니다.

 

 

FP6165는 Package가 DFN도 있지만, SOP-8L (EP)인 FP6165ADXR-G1이 제일 사용하기좋습니다.

먼저 가격도 DFN보다 저렴하며, Board에서 Test를 하거나, Debugging할때 Chip의 Pin이 밖으로 나와있기때문에

DFN보다 편리하며, 대부분의 고객이 SOP-8L (EP) Package를 사용하기에 납기에도 편리합니다.

 

 

 

The FP6165 is a high efficiency current mode synchronous buck PWM DC-DC regulator. 

The internal generated 0.6V precision feedback reference voltage is designed for low output voltage. 

Low RDS (ON) synchronous switch dramatically reduces conduction loss. 

To extend battery life for portable application, 100% duty cycle is supported for low-ropout operation.

Shutdown mode also helps saving the current consumption. 

The FP6165 is packaged in MSOP-10L, DFN-10L and SOP-8L to reduce PCB space.

 

 

 

• Input Voltage Range: 2.5 to 5.5V

• Adjustable Output Voltage From 0.6V to VIN

• Precision Feedback Reference Voltage: 0.6V (±2%)

• Output Current: 3A (Max.)

• Duty Cycle: 0~100%

• Internal Fixed PWM Frequency: 1.5MHz

• Low Quiescent Current: 100μA

• No Schottky Diode Required

• Built-in Soft Start

• Current Mode Operation

• Over Temperature Protection

• Package: MSOP-10L (EP), DFN-10L, SOP-8L (EP)

 

Function Description

Control Loop
The FP6165 is a high efficiency current mode synchronous buck regulator. Both the main (P-channel MOSFET) and synchronous (N-channel MOSFET) switches are built internally. 

With current mode operation, the PWM duty is controlled both by the error amplifier output and the peak inductor current. 

At the beginning of each cycle, the oscillator turn on the P-MOSFET switch to source current from VIN to SW output. 

 

Then, the chip starts to compare the inductor current with the error amplifier output. Once the inductor current is larger than 

the error amplifier output, the P-MOSFET switch is turned off. 

When the load current increases, the feedback voltage FB will slightly drop. 

 

This causes the error amplifier to output a higher current level until the prior mentioned peak inductor current reach the same level. 

The output voltage then can be sustained at the same.
When the top P-MOSFET switch is off, the bottom synchronous N-MOSFET switch is turned on.

Once the inductor current reverses, both top and bottom MOSFET will be turn off to leave the SW pin into high impedance state.
The FP6165’s current mode control loop also includes slope compensation to suppress sub-harmonic oscillations at high duty cycles. 

This slope compensation is achieved by adding a compensation ramp to the inductor current signal.

 

LDO Mode
The FP6165’s maximum duty cycle can reach 100%. 

That means the driver’s main switch is turn on through out whole clock cycle. 

Once the duty reaches 100%, the feedback path no longer controls the output voltage. 

The output voltage will be the input voltage minus the main switch voltage drop.

 

Over Current Protection
FP6165 limits the peak main switch current cycle by cycle. When over current occurs, chip will
turn off the main switch and turn the synchronous switch on until next cycle.

 

Short Circuit Protection
When the FB pin is drop below 300mV, the chip will tri-state the output pin SW automatically. 

After 300us rest to avoid over heating, chip will re-initiate PWM operation with soft start.

 

Power Good
The power good pin is an open-drain output. Connects a 100kΩ pull up resistor between VIN and
this pin to obtain a PGOOD voltage. 

When the output voltage is not within ±10% of setting output voltage, the PGOOD pin will be pulled down to ground immediately. 

After the output voltage is within ±10% of setting output voltage for 42.7μs (typ.), the PGOOD pin pull-down is turned off. 

Then it can be pulled up to VIN through external pull-high resister.
Connect this pin to AGND if not used.

 

Thermal Protection
FP6165 will shutdown automatically when the internal junction temperature reaches 150℃ to protect both the part and the system.

 

 

 

 

 

예로서 아래와 같은 Application이 있습니다.

 

 

Vin=5V, Vout=3.7V/2A
Efficiency=93%, Output Ripple=16mV

 

 

 

Vin=3.3V, Vout=1.8V/3A 
Operating Efficiency=83.5%, Output Ripple=12mV

 

 

 

 

아래는 spec sheet의 응용 회로도입니다.

 

 

 

 

 

PC Board Layout Checklist.

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

2. Place CIN near VIN pin as closely as possible to maintain input voltage steady and filter out the pulsing input current.

3. The resistive divider R1 and R2 must be connected to FB pin directly and as closely as possible. 

4. FB is a sensitive node. Please keep it away from switching node, SW. A good approach is to route the feedback trace

   on another PCB layer and have a ground plane between the top and feedback trace routing layer. 

   This reduces EMI radiation on to the DC-DC converter its own voltage feedback trace.

5. Keep the GND plates of CIN and COUT as close as possible. Then connect this to the ground plane (if one is used) 

   with several vias. 

   This reduces ground plane noise by preventing the switching currents from circulating through the ground plane. 

   It also reduces ground bounce at FP6165 by giving it a low impedance ground connection.

 

 

 

fp6165v071.pdf

0.66MB