NCP1010ST130T3G(2010) 데이터 시트보기 (PDF) - ON Semiconductor

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NCP1010ST130T3G
(Rev.:2010)

Self-Supplied Monolithic Switcher for Low Standby Power Offline SMPS

ON Semiconductor 

NCP1010, NCP1011, NCP1012, NCP1013, NCP1014

Full Latching Shutdown

Other applications require a full latching shutdown, e.g.

when an abnormal situation is detected (overtemperature

or overvoltage). This feature can easily be implemented

through two external transistors wired as a discrete SCR.

When the OVP level exceeds the Zener breakdown

OVP

Rhold

12 k

10 k

BAT54

voltage, the NPN biases the PNP and fires the equivalent

SCR, permanently bringing down the FB pin. The

switching pulses are disabled until the user unplugs the

power supply.

1

8

2

7

3

4

5

Drain

10 k

+

CVcc

Figure 24. Two Bipolars Ensure a Total Latch--Off of the SMPS in Presence of an OVP

Rhold ensures that the SCR stays on when fired. The bias

current flowing through Rhold should be small enough to let

the VCC ramp up (8.5 V) and down (7.5 V) when the SCR

is fired. The NPN base can also receive a signal from a

temperature sensor. Typical bipolars can be MMBT2222

and MMBT2907 for the discrete latch. The MMBT3946

features two bipolars NPN+PNP in the same package and

could also be used.

Power Dissipation and Heatsinking

The NCP101X welcomes two dissipating terms, the DSS

current--source (when active) and the MOSFET. Thus,

Ptot = PDSS + PMOSFET. When the PDIP--7 package is

surrounded by copper, it becomes possible to drop its

thermal resistance junction--to--ambient, RθJA down

to 75C/W and thus dissipate more power. The

maximum power the device can thus evacuate is:

Pmax

=

TJmax

− Tambmax

RθJA

(eq. 12) which gives around

1.0 W for an ambient of 50C. The losses inherent to the

MOSFET RDSon can be evaluated using the following

formula:

Pmos

=

1

3

·

Ip2

·

d

·

RDSon

(eq. 13) , where Ip

is the worse case peak current (at the lowest line input), d is

the converter operating duty--cycle and RDSon, the

MOSFET resistance for TJ = 100C. This formula is only

valid for Discontinuous Conduction Mode (DCM)

operation where the turn--on losses are null (the primary

current is zero when you restart the MOSFET). Figure 25

gives a possible layout to help drop the thermal resistance.

When measured on a 35 mm (1 oz) copper thickness PCB,

we obtained a thermal resistance of 75C/W.

Figure 25. A Possible PCB Arrangement to Reduce the Thermal Resistance Junction--to--Ambient

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