FP6153-3A, 36V,Synchronous Step-Down Converter에 대한 고찰

 

 

오늘은 FP6153-3A, 36V, Synchronous Step-Down Converter에 대한 고찰을 해 보겠습니다.

FP6153는 High Voltage(HV) input, 3A, 36V, Synchronous Step-Down Converter로 아래와 같은 특성을 지니고 있습니다.

 

The FP6153 is a buck regulator with a built in internal power MOSFET. It achieves 3A continuous
output current over a wide input supply range with excellent load and line regulation. Current mode
operation provides fast transient response and eases loop stabilization. A wide switching frequency
range allows efficiency and external component size to be optimized. The device includes under
voltage lockout and thermal shutdown protection. The regulator only consumes 8μA supply current in
shutdown mode. The FP6153 requires a minimum number of readily available external components to
complete a 3A buck regulator solution.

 

 

• Synchronous Buck Converter

• Operating Input Range; 4.5V to 36V

• Feedback Reference Voltage; 0.808V(+/-2%)

• 3A Output Current

• Duty Cycle; 90% max

• Built-in Soft-Start

• Built-in 100mΩ/75mΩ Power MOSFET Switch, No Schottky Diode Required

• 200KHz to 1.5MHz Adjustable Switching Frequency

• Built-in Soft Start

• Cycle-by-Cycle Current Limit

• Input Under Voltage Lockout

• Over Current Protection(OCP), Short Circuit Protection(SCP), Over Temperature Protection(OTP)

• Internal soft-start: 2ms

• Available SOP8 With Exposed PAD

 

 

Function Description
The FP6153 is a synchronous current-mode buck regulator. 

It regulates input voltages from 4.5V to 36V down to an output voltage as low as 0.808V, and is able to supply up

 to 3A of load current. 

The FP6153 uses current-mode control to regulate the output voltage. 

The output voltage is measured at FB through a resistive voltage divider and amplified by the internal error amplifier. 

The output current of the transconductance error amplifier is presented at COMP where a network compensates the
regulation control system. 

The voltage at COMP is compared to the switch current measured internally to control the output voltage. 

The converter uses internal n-channel MOSFET switches to step-down the input voltage to the regulated output voltage. 

Since the MOSFET requires a gate voltage greater than the input voltage, a boost capacitor connected 

between SW and BS drives the gate. 

The capacitor is charged from the internal regulator when the SW pin is low.

 

Output Voltage (VOUT)
The output voltage is set using a resistive voltage divider from the output voltage to FB.

 

 

Enable Mode / Shutdown Mode
The FP6153 has a dedicated enable control pin, EN. 

And that can be enabled or disabled by EN pulling high or low. 

For automatic start up, the pin EN would be tied to VIN through a 100KΩ resistor, and be pulled low for disable 

automatic start up function. 

When EN floating, the EN is pulled up to about 2.0V by an internal 1μA current source and the FP6153 is enabled.

 

Boost High-Side Gate Drive (BS)
Since the MOSFET requires a gate voltage greater than the input voltage, connect a flying bootstrap capacitor between SW and 

BS to provide the gate-drive voltage to the high-side n-channel MOSFET switch. 

The capacitor is alternately charged from the internal regulator. On startup, an internal low-side switch connects SW to ground 

and charges the BST capacitor to internal regulated voltage. 

Once the BST capacitor is charged, and the internal low-side switch is turned off, the BST capacitor voltage provides the necessary

 enhancement voltage to turn on the high-side switch.

 

 

Thermal Shutdown Protection
The FP6153 features integrated thermal shutdown protection. 

When the IC junction temperature exceeds +150°C, thermal shutdown protection will be triggered. 

The internal power MOSFET is then turned off to limit the device power dissipation (PD). 

Once thermal shutdown occurs, this device can go back to normal operation until the junction temperature 

drops below +100°C approximately.

 

Programmable Oscillator
The FP6153 oscillator frequency (200kHz~1.5MHz adjustable switching frequency) is set by an external resistor, 

RT from RT pin to GND.

 

 

Application Information
Input Capacitor Selection
The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the AC current to the step-down converter while maintaining the DC input voltage. 

 

 

Use low ESR
capacitors for the best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice.
The input capacitor can be electrolytic, tantalum or ceramic. When using electrolytic, tantalum, or small volume of high-quality ceramic capacitors, i.e. 0.1μF, should be as close to the IC as possible.
When using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent 

excessive voltage ripple at input.

 

 

Inductor Selection
The inductor is required to supply constant current to the output load while being driven by the switched input voltage. 

A larger value inductor will result in less ripple current that will result in lower output ripple voltage. 

However, the larger value inductor will have a larger physical size, higher series resistance, and / or lower saturation current. 

A good rule for determining the inductance to use is to allow the peak-to-peak ripple current in the inductor 

to be approximately 30% of the maximum switch current limit.

 

 

Output Capacitor Selection
The output capacitor is required to maintain the DC output voltage. 

Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output
voltage ripple low.

In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. 

The output voltage ripple is mainly caused by the capacitance. In the case of tantalum or electrolytic capacitors, 

the ESR dominates the impedance at the switching frequency.

 

 

 

 

 

아래는 Application Demo Board로서

Vin=30V, Vout=5V / Iout=2A로 spec을 정해서 application 하면,

 

Frequency=326kHz, Efficiency=90.4%, Output Ripple=43mV, Temperature IC1=61℃ L1=48℃ 입니다.

 

 

 

 

아래는 spec sheet의 응용 회로도입니다.

 

 

PC Board Layout Checklist
1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct and wide.
2. Place CIN near IN Pin as closely as possible. To maintain input voltage steady and filter out the pulsing input current.
3. The resistive divider R2and R4 must be connected to FB pin directly 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 layer and to have a ground plane between the top
   layer and the layer on which the feedback trace is routed. 

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

 

 

FP6153V063-G1.pdf

0.56MB