Rev E
02/12
TNY253/254/255
2
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 inter-
nally generated 5.8 V 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 1.5 V 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, 5.8 V Regulator, Undervoltage circuit,
Hysteretic Over Temperature Protection, Current Limit circuit,
Leading Edge Blanking, and a 700 V 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 Maxi-
mum 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 oscilla-
tor frequency doubles (except for TNY255 which remains at
130 kHz). 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 1.5 V. 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
S
R
Q
DCMAX
BYPASS
+
-
VILIMIT
LEADING
EDGE
BLANKING
THERMAL
SHUTDOWN
+
-
DRAIN
REGULATOR
5.8 V
UNDERVOLTAGE
1.5 V + VTH
ENABLE
Q
50 A
PI-2199-031501
ENABLE
8
5
7
6
DRAIN
SOURCE
SOURCE
SOURCE
1
4
2
3
SOURCE
SOURCE
BYPASS
P Package (DIP-8)
G Package (SMD-8)
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