SSC2005SC datasheet(14/19 Pages) SANKEN

14 / 19 page

SSC2005SC

SSC2005SC-DS Rev.1.1

SANKEN ELECTRIC CO.,LTD.

Feb. 06, 2015

 OUT Pin Peripheral Circuit (Gate Drive Circuit)

Figure 9-2 shows the OUT pin peripheral circuit.

The OUT pin is the gate drive output which can drive an

external power MOSFET directly.

The maximum output voltage of the OUT pin is the VCC

pin voltage. The maximum current is −500 mA for

source and 1 A for sink, respectively.

R1 is for source current limiting. Both R2 and D2 are for

sink current limiting. The values of these components are

adjusted to decrease the ringing of Gate pin voltage and

the EMI noise. The reference value is several ohms to

several dozen ohms.

R3 is used to prevent malfunctions due to steep dv/dt at

turn-off of the power MOSFET, and the resistor is

connected near the power MOSFET, between the gate

and source. The reference value of R3 is from 10 kΩ to

100 kΩ.

R1, R2, D2 and R3 are affected by the printed circuit

board trace layout and the power MOSFET capacitance.

Thus, the optimal values should be adjusted under actual

operation of the application.

RCS

GND

OUT

Figure 9-2 The OUT pin peripheral circuit.

 VCC Pin Peripheral Circuit

Figure 9-3 shows the VCC pin peripheral circuit.

The VCC pin is power supply input. The VCC pin is

supplied from an external power.

When the VCC pin and the external power supply are

distant from each other, placing a film capacitor Cf

between the

VCC pin and

the

GND

pin is

recommended.

The value of capacitor Cf is set approximately 0.47 μF,

in order to reduce the switching noise.

GND

VCC

External

Power

Supply

Figure 9-3 The VCC pin peripheral circuit

 Power MOSFET : Q1

Choose a power MOSFET having proper margin of

VDSS against output voltage, VOUT. The size of heat

sink is chosen taking into account some loss by

switching and ON resistance of the power MOSFET.

The RMS value of drain current, IDRMS is expressed as

follows:

)

MIN

(

ACRMS

OUT

DRMS







＝

OUT

ACRMS(MIN)



－

(A)

(9)

The loss, PRDS(ON), by on-resistance of the power

MOSFET is calculated as follows:





125

)

(

DRSM

)

(

RDS







(W)

(10)

where,

VACRMS(MIN)

: Minimum AC input voltage rms value (V)

POUT

: Output power (W)

: Efficiency of PFC

RDS(ON)125°C

: ON resistance of the power MOSFET at

Tch = 125 °C (Ω)

 Boost Diode: D

Choose a boost diode having proper margin of a peak

reverse voltage VRSM against output voltage, VOUT.

A fast recovery diode is recommended to reduce the

switching noise and loss. Please ask our staff about

our lineup. The size of heat sink is chosen taking into

account some loss by VF and recovery current of the

boost diode.

The loss of VF, PDFW, is expressed as follows:

OUT

DFW





(W)

(11)

Where,

: Forward voltage of boost diode (V)

IOUT : Out put current (A)

 Bypass Diode: D

BYP

A Bypass diode protects a boost diode from a large

current such as an inrush current. A high surge current

tolerance diode is recommended. Please ask our staff

about our lineup.

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