Energy Efﬁcient, Off-Line Switcher with
Enhanced Flexibility and Extended Power Range
Lowest System Cost with Enhanced Flexibility
• Simple ON/OFF control, no loop compensation needed
• Selectable current limit through BP/M capacitor value
- Higher current limit extends peak power or, in open
frame applications, maximum continuous power
- Lower current limit improves efﬁciency in enclosed
- Allows optimum TinySwitch-III choice by swapping
devices with no other circuit redesign
HV DC Input
• Tight I2f parameter tolerance reduces system cost
Figure 1. Typical Standby Application.
- Maximizes MOSFET and magnetics power delivery
- Minimizes max overload power, reducing cost of
transformer, primary clamp & secondary components
OUTPUT POWER TABLE
• ON-time extension – extends low line regulation range/
230 VAC ±15%
hold-up time to reduce input bulk capacitance
Self-biased: no bias winding or bias components
Frequency jittering reduces EMI ﬁlter costs
Pin-out simpliﬁes heatsinking to the PCB
Adapter1 Open Adapter1 Open
• SOURCE pins are electrically quiet for low EMI
TNY274 P or G 6 W 11 W 5 W 8.5 W
TNY275 P or G 8.5 W 15 W 6 W 11.5 W
Enhanced Safety and Reliability Features
• Accurate hysteretic thermal shutdown protection with
automatic recovery eliminates need for manual reset
TNY276 P or G 10 W 19 W
TNY277 P or G 13 W 23.5 W
• Improved auto-restart delivers <3% of maximum power
TNY278 P or G 16 W 28 W 10 W 21.5 W
in short circuit and open loop fault conditions
TNY279 P or G 18 W 32 W 12 W 25 W
• Output overvoltage shutdown with optional Zener
• Line under-voltage detect threshold set using a single
TNY280 P or G 20 W 36.5 W 14 W 28.5 W
• Very low component count enhances reliability and
enables single-sided printed circuit board layout
• High bandwidth provides fast turn on with no overshoot
and excellent transient load response
Table 1. Notes: 1. Minimum continuous power in a typical non-
ventilated enclosed adapter measured at 50 °C ambient. Use of an
external heatsink will increase power capability 2. Minimum peak
power capability in any design or minimum continuous power in an
open frame design (see Key Application Considerations). 3. Packages:
P: DIP-8C, G: SMD-8C. See Part Ordering Information.
• Extended creepage between DRAIN and all other pins
improves ﬁeld reliability
EcoSmart®– Extremely Energy Efﬁcient
• Easily meets all global energy efﬁciency regulations
• No-load <150 mW at 265 VAC without bias winding,
<50 mW with bias winding
• ON/OFF control provides constant efﬁciency down to
very light loads – ideal for mandatory CEC regulations
and 1 W PC standby requirements
• Chargers/adapters for cell/cordless phones, PDAs, digital
cameras, MP3/portable audio, shavers, etc.
• PC Standby and other auxiliary supplies
• DVD/PVR and other low power set top decoders
• Supplies for appliances, industrial systems, metering, etc.
TinySwitch-III incorporates a 700 V power MOSFET, oscillator,
high voltage switched current source, current limit (user
selectable) and thermal shutdown circuitry. The IC family uses
an ON/OFF control scheme and offers a design ﬂexible solution
with a low system cost and extended power capability.
DataSheet4 U .com
1.0 V + VT
Figure 2. Functional Block Diagram.
Pin Functional Description
DRAIN (D) Pin:
This pin is the power MOSFET drain connection. It provides
internal operating current for both start-up and steady-state
BYPASS/MULTI-FUNCTION (BP/M) Pin:
This pin has multiple functions:
1. It is the connection point for an external bypass capacitor
for the internally generated 5.85 V supply.
2. It is a mode selector for the current limit value, depending
on the value of the capacitance added. Use of a 0.1 µF
capacitor results in the standard current limit value. Use of
a 1 µF capacitor results in the current limit being reduced to
that of the next smaller device size. Use of a 10 µF capacitor
results in the current limit being increased to that of the next
larger device size for TNY275-280.
3. It provides a shutdown function. When the current into the
bypass pin exceeds 5.5 mA, the device latches off until the
BP/M voltage drops below 4.9 V, during a power down.
DataSheet4U.Tchoims can be used to provide an output overvoltage function
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P Package (DIP-8C)
G Package (SMD-8C)
Figure 3. Pin Conﬁguration.
with a Zener connected from the BP/M pin to a bias winding
ENABLE/UNDER-VOLTAGE (EN/UV) Pin:
This pin has dual functions: enable input and line under-voltage
sense. During normal operation, switching of the power
MOSFET is controlled by this pin. MOSFET switching is
terminated when a current greater than a threshold current is
drawn from this pin. Switching resumes when the current being
pulled from the pin drops to less than a threshold current. A
modulation of the threshold current reduces group pulsing. The
threshold current is between 60 µA and 115 µA.
The EN/UVpin also senses line under-voltage conditions through
an external resistor connected to the DC line voltage. If there is
no external resistor connected to this pin, TinySwitch-III detects
its absence and disables the line under-voltage function.
minadxicimateusmthdeubtyegciyncnleinsgigonfaela(cDhCcMyAcXle) .and the clock signal that
The oscillator incorporates circuitry that introduces a small
amount of frequency jitter, typically 8 kHz peak-to-peak, to
minimize EMI emission. The modulation rate of the frequency
jitter is set to 1 kHz to optimize EMI reduction for both average
and quasi-peak emissions. The frequency jitter should be
measured with the oscilloscope triggered at the falling edge of
the DRAIN waveform. The waveform in Figure 4 illustrates
the frequency jitter.
SOURCE (S) Pin:
Enable Input and Current Limit State Machine
This pin is internally connected to the output MOSFET source
The enable input circuit at the EN/UV pin consists of a low
for high voltage power return and control circuit common.
impedance source follower output set at 1.2 V. The current
through the source follower is limited to 115 µA. When the
current out of this pin exceeds the threshold current, a low
logic level (disable) is generated at the output of the enable
circuit, until the current out of this pin is reduced to less than
TinySwitch-III combines a high voltage power MOSFET switch
with a power supply controller in one device. Unlike conventional
PWM (pulse width modulator) controllers, it uses a simple
ON/OFF control to regulate the output voltage.
the threshold current. This enable circuit output is sampled
at the beginning of each cycle on the rising edge of the clock
signal. If high, the power MOSFET is turned on for that cycle
(enabled). If low, the power MOSFET remains off (disabled).
Since the sampling is done only at the beginning of each cycle,
The controller consists of an oscillator, enable circuit (sense and
logic), current limit state machine, 5.85 V regulator, BYPASS/
subsequent changes in the EN/UV pin voltage or current during
the remainder of the cycle are ignored.
current limit level accordingly in discrete amounts.
The typical oscillator frequency is internally set to an average
of 132 kHz. Two signals are generated from the oscillator: the
Under most operating conditions (except when close to no-load),
the low impedance of the source follower keeps the voltage on
600 the EN/UV pin from going much below 1.2 V in the disabled
state. This improves the response time of the optocoupler that
is usually connected to this pin.
5.85 V Regulator and 6.4 V Shunt Voltage Clamp
300 The 5.85 V regulator charges the bypass capacitor connected
to the BYPASS pin to 5.85 V by drawing a current from the
200 voltage on the DRAIN pin whenever the MOSFET is off. The
BYPASS/MULTI-FUNCTION pin is the internal supply voltage
node. When the MOSFET is on, the device operates from the
energy stored in the bypass capacitor. Extremely low power
consumption of the internal circuitry allows TinySwitch-III to
operate continuously from current it takes from the DRAIN
pin. A bypass capacitor value of 0.1 µF is sufﬁcient for both
high frequency decoupling and energy storage.
0 5 10
DataSheet4FUig.ucroem4. Frequency Jitter.
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