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

Vout

VCC

Vbulk

Q1

Rupper

5 ms

+ RC

−

+

Vlatch

IBO

To permanent

latch

BO

NTC Rlower

+

−

+

VBO

20 ms

Filter

UVLO

BO_OK

Figure 37. Adding a Comparator on the BO Pin Offers a Way to Latch−off the Controller

Latch−off Protection

There are some situations under which should be the

converter fully turned−off and stay latched. This can happen

in presence of an over−voltage (the feedback loop is

drifting) or when an over temperature is detected. Due to the

addition of a comparator on the BO pin, a simple external

circuit can lift up this pin above VLATCH (4 V typical) and

permanently disable pulses. The VCC pin voltage needs to

be cycled down below 6.6 V typically to reset the controller.

On Figure 37, Q1 is blocked and does not bother the BO

measurement as long as the NTC and the optocoupler are not

activated. As soon as the secondary optocoupler senses an

OVP condition, or the NTC reacts to a high ambient

temperature, Q1 base is pulled down to ground and the BO

pin goes up, permanently latching off the controller.

Overload Protection

This resonant controller features a proprietary overload

protection system that assures application power stage

safety under all possible fault conditions. This system

consists of an OLP input for primary current sensing and a

Discharge pin to enable a controlled frequency shift via the

Rt pin once an overload condition occurs. Internal block

diagram of the overload system with a typical application

connection can be seen in Figures 39 and 40.

The primary current is sensed indirectly using charge

pump (R1, R2, D1, D2, C1 and C2) connected between

resonant capacitor and OLP input. When the primary current

increases, the voltage on the OLP input grows up as well. It

should be noted that other primary current sensing methods

(like current sense transformer) can be used instead of

charge pump if required by application.

The OCP network (Rshift, Rocp, Cocp), that is present on

the Rt pin in addition to the Fmin adjust resistor and Soft

Start network, plays important role in overload system

implementation. This additional network is used to allow

independent OCP and Soft Start parameters adjustment. The

OCP network can be omitted in some applications where the

Soft Start capacitor with low capacitance is used. The Rshift

resistor is then connected directly to the Soft Start capacitor

to implement frequency shift during overload.

Overload protection system implemented on OLP input

composes of three particular subsystems with following

functionality:

1. The fault timer charging current is activated when

the OLP input voltage exceeds 1 V threshold. The

controller stops operation and enters

auto−recovery phase when the overload conditions

last for longer time than the adjusted fault timer

duration on Ctimer pin (Ct charged to 4 V). The

controller then places full restart (including soft

start) when auto−recovery period elapses i.e. when

Ctimer capacitor discharges back below 1 V.

2. The second overload protection mode is activated

additionally to the first one i.e. when the OLP pin

voltage exceeds 1 V. The frequency shift is

implemented via Rt and Discharge pins in this case

by pulling the discharge switch down from

Vref_Rt to ground – refer also to Figure 38 for

Vdisable evaluation with OLP input voltage. The

Discharge pin is connected to the Rocp and Cocp

network, that is present on the Rt pin, via resistor

Rshift. This configuration allows to adjust OCP

frequency shift depth and reaction time and thus

ease overload system implementation in any

application.

The Rt pin OCP components are normally

designed in such a way that the OCP system shifts

and regulates the operating frequency of the LLC

converter during overload or secondary side short

circuit conditions to maintain primary current at a

save level and keep zero voltage switching

operation.

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