TNY175PN 데이터 시트보기 (PDF) - Power Integrations, Inc

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TNY175PN

TinySwitch-LT Family Energy Efficient, Offline Switcher with Enhanced Flexibility and Extended Power Range®

Power Integrations, Inc 

for improved accuracy.

ON/OFF Operation with Current Limit State Machine

The internal clock of the TinySwitch-LT runs all the time. At the

beginning of each clock cycle, it samples the EN pin to decide

whether or not to implement a switch cycle, and based on the

sequence of samples over multiple cycles, it determines the

appropriate current limit. At high loads, the state machine sets

the current limit to its highest value. At lighter loads, the state

machine sets the current limit to reduced values.

VEN

CLOCK

DMAX

IDRAIN

VDRAIN

Figure 6. Operation at Near Maximum Loading.

PI-2749-050301

TNY174-180

At near maximum load, TinySwitch-LT will conduct during

nearly all of its clock cycles (Figure 6). At slightly lower load,

it will “skip” additional cycles in order to maintain voltage

regulation at the power supply output (Figure 7). At medium

loads, cycles will be skipped and the current limit will be reduced

(Figure 8). At very light loads, the current limit will be reduced

even further (Figure 9). Only a small percentage of cycles will

occur to satisfy the power consumption of the power supply.

The response time of the ON/OFF control scheme is very fast

compared to PWM control. This provides tight regulation and

excellent transient response.

Power Up/Down

The TinySwitch-LT 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.

Figure 10 shows typical power up timing waveforms.

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, the power MOSFET will switch for 64

ms after the output loses regulation.

VEN

CLOCK

DMAX

VEN

CLOCK

DCMAX

IDRAIN

IDRAIN

VDRAIN

VDRAIN

PI-2667-090700

Figure 7. Operation at Moderately Heavy Loading.

Figure 8. Operation at Medium Loading.

PI-2377-082305

A

08/07

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