TNY274PG Ver la hoja de datos (PDF) - Power Integrations, Inc

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Fabricante

TNY274PG

Enhanced/ Energy Efficient/ Low Power Off-line Switcher

Power Integrations, Inc 

Power Up/Down

The TinySwitch-III requires only a 0.1 µF capacitor on the

BYPASS/MULTI-FUNCTION pin to operate with standard

current limit. Because of its small size, the time to charge this

capacitor is kept to an absolute minimum, typically 0.6 ms. The

time to charge will vary in proportion to the BYPASS/MULTI-

FUNCTION pin capacitor value when selecting different current

limits. Due to the high bandwidth of the ON/OFF feedback,

there is no overshoot at the power supply output. When an

external resistor (4 MΩ) is connected from the positive DC

input to the EN/UV pin, the power MOSFET switching will

be delayed during power-up until the DC line voltage exceeds

the threshold (100 V). Figures 10 and 11 show the power-up

timing waveform in applications with and without an external

resistor (4 MΩ) connected to the EN/UV pin.

Under startup and overload conditions, when the conduction time

is less than 400 ns, the device reduces the switching frequency

to maintain control of the peak drain current.

During power-down, when an external resistor is used, the

power MOSFET will switch for 64 ms after the output loses

regulation. The power MOSFET will then remain off without

any glitches since the under-voltage function prohibits restart

when the line voltage is low.

Figure 12 illustrates a typical power-down timing waveform.

Figure 13 illustrates a very slow power-down timing waveform

as in standby applications. The external resistor (4 MΩ) is

connected to the EN/UV pin in this case to prevent unwanted

restarts.

No bias winding is needed to provide power to the chip

because it draws the power directly from the DRAIN pin (see

TNY274-280

Functional Description above). This has two main benefits.

First, for a nominal application, this eliminates the cost of a

bias winding and associated components. Secondly, for battery

charger applications, the current-voltage characteristic often

allows the output voltage to fall close to zero volts while still

delivering power. TinySwitch-III accomplishes this without a

forward bias winding and its many associated components. For

applications that require very low no-load power consumption

(50 mW), a resistor from a bias winding to the BYPASS/

MULTI-FUNCTION pin can provide the power to the chip.

The minimum recommended current supplied is 1 mA. The

BYPASS/MULTI-FUNCTION pin in this case will be clamped

at 6.4 V. This method will eliminate the power draw from the

DRAIN pin, thereby reducing the no-load power consumption

and improving full-load efficiency.

Current Limit Operation

Each switching cycle is terminated when the DRAIN current

reaches the current limit of the device. Current limit operation

provides good line ripple rejection and relatively constant power

delivery independent of input voltage.

BYPASS/MULTI-FUNCTION Pin Capacitor

The BYPASS/MULTI-FUNCTION pin can use a ceramic

capacitor as small as 0.1 µF for decoupling the internal power

supply of the device. A larger capacitor size can be used to adjust

the current limit. For TNY275-280, a 1 µF BP/M pin capacitor

will select a lower current limit equal to the standard current

limit of the next smaller device and a 10 µF BP/M pin capacitor

will select a higher current limit equal to the standard current

limit of the next larger device. The higher current limit level of

the TNY280 is set to 850 mA typical. The TNY274 MOSFET

does not have the capability for increased current limit so this

feature is not available in this device.

E

2/06

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