NR263S Datasheet, PDF(15/29 Page) Sanken electric – Light Load High Efficiency Synchronous Buck Regulator IC

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NR263S Datasheet, PDF (15/29 Pages) Sanken electric – Light Load High Efficiency Synchronous Buck Regulator IC

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NNNRNN2N63S

7.4 Over current and Short circuit protection Function (OCP & HICCUP)

An OCP characteristic is shown in the Fig7-6. The "drooping type" over-current-protection is equipped in the

NR263S. As for the over-current-protection circuit,this IC detects a peak current to flow to the switching-transistor.

When peak current exceeds setup value, a Ton-period of the transistor is made to shorten forcibly, and an output

voltage VO is made to decrease, and an output current is restricted. In this case, by the decline of the output voltage

VO, when a VO-terminal- voltage VO decreases to 3.5V 70% of the internal-reference -voltage (5V) , by the

reducing of the switching-frequency (the FDOWN mode),the "drooping characteristic" is improved in the low output

voltage.As shown in the Fig12, Moreover, when a VO-terminal-voltage VO decreases more and it becomes under

30% of the internal reference voltage (*5Vâ1.5V), the Soft-start capacitor CSS is charged by internal current source

ISS=5Î¼A.When a SS-terminal-voltage VSS rises to 2.2V, the interval-operation mode (HICCUP) becomes effective,

and the continuous-switching-operation is canceled. After that, the soft-start capacitor CSS is discharged by the

constant current (=-2.5[Î¼A]) , and the suspension-period of interval-operation is set up. The soft-start is restarted

when a SS-terminal-voltage VSS decreases to 0.23[V]. The interval-operation mode (HICCUP) is maintained due to

this repetition. By becoming the interval-operation mode, part stress such as heat-generation can be eased. An output

voltage is resumed to normal condition automatically when over-current condition is canceled. * When a HICCUP

function is invalidated, the short-current becomes continuously such as a characteristic of the red line in the Fig7-7.

Fig. 7-6 OCP (HICCUP Mode) Timing Chart

HICCUP

Fig. 7-7 OCP characteristic curve (Condition example ï¼VIN=12V, VO=5V)

NR263S series-DSE Rev.1.0

SANKEN ELECTRIC CO.,LTD

2016.03.09

http://www.sanken-ele.co.jp/en/

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