NCP1398CDR2G データシートの表示（PDF） - ON Semiconductor

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NCP1398CDR2G

High Performance Resonant Mode Controller with Integrated High-Voltage Drivers

ON Semiconductor 

NCP1398B/C

Voltage−Controlled Oscillator

The VCO section features a high−speed circuitry allowing

operation from 100 kHz up to 1.5 MHz. However, as a

division by two internally creates the two Q and /Q outputs,

the final effective signal on output Mlower and Mupper

VDD

switches between 50 kHz and 750 kHz. The VCO is

configured in such a way that if the feedback pin voltage

goes up, the switching frequency also goes up. Figure 23

shows internal architecture of the VCO.

Imin

ONtime

Ict

Vref

Rt

modulation

sets Fmin

for Vfb < 1 V

+

SS disch.

I Fb

Ct

VDD

-

+

DQ

Clk Q

RDT DT

Sets DT

Fmax

Sets max.

FSW clamp

VCC

FB

Idt

Vref

VDD

Vref

+

+

−

Ct

I Rt + I FTbo skip

I Fmax comparator

Vfb_min

+

-

+

Vb_fault

FB fault

RFB

20 k

SQ

RQ

A

B

to DRV logic

GND

Figure 23. The Simplified VCO Architecture

When designing a resonant SMPS the designer needs to

program the minimum and maximum switching frequencies

to assure correct and reliable operation. The minimum

switching frequency clamp adjustment accuracy is critical

because this parameter defines maximum power the

converter can deliver for given bulk voltage. The Fmin

parameter is thus trimmed to ±3% tolerance in the NCP1398

controller to assure application reproducibility in

manufacturing. The minimum frequency clamp, that is fully

user adjustable via a resistor connected to the Rt pin, is

reached when the feedback loop is not closed. It can happen

during the startup sequence, a strong output transient

loading or during short−circuit conditions.

The maximum operating frequency clamp, that is defined

by the value of resistor connected between Fmax pin and

GND, dictates the minimum output power that is needed to

maintain output voltage regulation. This parameter, adjusts

the threshold of when the part enters skip mode. Precision of

the Fmax clamp is thus guaranteed to ±12 %.

The operating frequency is modulated by the secondary

regulator via the FB pin in most applications. The frequency

changes between minimum (Fmin) and maximum (Fmax)

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