FDMF3035 datasheet(15/21 Pages) ONSEMI

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Application Information

Decoupling Capacitor for PVCC & VCC

For the supply inputs (PVCC and VCC pins), local

decoupling capacitors are required to supply the peak

driving current and to reduce noise during switching

operation. Use at least 0.68 ~ 1 µF / 0402 ~ 0603 / X5R

~ X7R multi-layer ceramic capacitors for both power

rails. Keep these capacitors close to the PVCC and

VCC pins and PGND and AGND copper planes. If the

de-coupling capacitors need to be located on the bottom

side of board, place through-hole vias on each pad

connecting top side and bottom side PVCC and VCC

nodes with low impedance current paths, see Figure 30

and Figure 31.

The supply voltage range on PVCC and VCC is 4.5 V ~

5.5 V, and typically 5 V for normal applications.

R-C Filter on VCC

The PVCC pin provides power to the gate drive of the

high-side and low-side power MOSFETs. In most cases,

PVCC can be connected directly to VCC, which is the

pin that provides power to the analog and logic blocks of

the driver. To avoid switching noise injection from PVCC

into VCC, a filter resistor can be inserted between

PVCC and VCC decoupling capacitors.

Recommended filter resistor value range is 0 ~ 4.7

Ω,

typically 0

Ω for most applications.

Bootstrap Circuit

The bootstrap circuit uses a charge storage capacitor

(CBOOT). A bootstrap capacitor of 0.1 ~ 0.22 µF / 0402 ~

0603 / X5R ~ X7R is usually appropriate for most

switching applications. A series bootstrap resistor may

be needed for specific applications to lower high-side

MOSFET switching speed. The boot resistor is required

when the SPS is switching above 15 V VIN; when it is

effective at controlling VSW overshoot. RBOOT value from

zero to 4.7

Ω is typically recommended to reduce

excessive voltage spike and ringing on the SW node. A

higher RBOOT value can cause lower efficiency due to

high switching loss of high-side MOSFET.

Do not add a capacitor or resistor between the BOOT

pin and GND.

PWM (Input)

The PWM pin recognizes three different logic levels

from PWM controller: HIGH, LOW, and 3-state. When

the PWM pin receives a HIGH command, the gate

driver turns on the high-side MOSFET. When the PWM

pin receives a LOW command, the gate driver turns on

the low-side MOSFET. When the PWM pin receives a

voltage signal inside of the 3-state window (VTRI_Window)

and exceeds the 3-state hold-off time, the gate driver

turns off both high-side and low-side MOSFETs. To

recognize the high-impedance 3-state signal from the

controller, the PWM pin has an internal resistor divider

from VCC to PWM to AGND. The resistor divider sets

a voltage level on the PWM pin inside the 3-state

window when the PWM signal from the controller is

high-impedance.

FCCM (Input)

When the FCCM pin is set HIGH, the driver IC Zero

Cross Detect (ZCD) comparator is disabled and the

high-side and low-side MOSFETs switch in FCCM

(Forced CCM) and follows the PWM signal. When the

FCCM pin is set LOW, the low-side MOSFET turns off

when the SPS driver detects negative inductor current

during the low-side MOSFET turn-on period. This

operating mode is commonly referred to as diode

emulation. The diode emulation feature allows for higher

converter efficiency during light-load condition and PFM

/ DCM operation.

Applications that require diode emulation and/or low

shutdown current should actively drive the FCCM pin

from a PWM controller. Do not add any noise filter

capacitor on the FCCM pin.

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