TNY255P datasheet(2/20 Pages) POWERINT

2 / 20 page

7/01

TNY253/254/255

Figure 2. Functional Block Diagram.

Figure 3. Pin Configuration.

Pin Functional Description

DRAIN (D) Pin:

Power MOSFET drain connection. Provides internal operating

current for both start-up and steady-state operation.

BYPASS (BP) Pin:

Connection point for an external bypass capacitor for the

internally generated 5.8V supply. Bypass pin is not intended

for sourcing supply current to external circuitry.

ENABLE (EN) Pin:

The power MOSFET switching can be terminated by pulling

this pin low. The I-V characteristic of this pin is equivalent to

a voltage source of approximately 1.5V with a source current

clamp of 50

µA.

SOURCE (S) Pin:

Power MOSFET source connection. Primary return.

TinySwitch Functional Description

TinySwitch is intended for low power off-line applications. It

combines a high voltage power MOSFET switch with a power

supply controller in one device. Unlike a conventional PWM

(Pulse Width Modulator) controller, the TinySwitch uses a

simple ON/OFF control to regulate the output voltage.

The TinySwitch controller consists of an Oscillator, Enable

(Sense and Logic) circuit, 5.8V Regulator, Under-Voltage

circuit, Hysteretic Over Temperature Protection, Current Limit

circuit, Leading Edge Blanking, and a 700V power MOSFET.

Figure 2 shows a functional block diagram with the most

important features.

Oscillator

The oscillator frequency is internally set at 44 kHz (130 kHz for

the TNY255). The two signals of interest are the Maximum

Duty Cycle signal (D

MAX) which runs at typically 67% duty

cycle and the Clock signal that indicates the beginning of each

cycle. When cycles are skipped (see below), the oscillator

frequency doubles (except for TNY255 which remains at

130kHz). This increases the sampling rate at the ENABLE pin

for faster loop response.

Enable (Sense and Logic)

The ENABLE pin circuit has a source follower input stage set

at 1.5V. The input current is clamped by a current source set

at 50

µA with 10 µA hysteresis. The output of the enable sense

PI-2197-061898

CLOCK

OSCILLATOR

5.8 V

5.1 V

SOURCE

DCMAX

BYPASS

LIMIT

LEADING

EDGE

BLANKING

THERMAL

SHUTDOWN

DRAIN

REGULATOR

5.8 V

UNDER-VOLTAGE

1.5 V + VTH

ENABLE

µA

PI-2199-031501

ENABLE

DRAIN

SOURCE

BYPASS

P Package (DIP-8)

G Package (SMD-8)

TNY255P Datasheet(PDF) 2 Page - Power Integrations, Inc.

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