Off-Line Switcher. TNY280GN Datasheet
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
• Tight I2f parameter tolerance reduces system cost
• Maximizes MOSFET and magnetics power delivery
• Minimizes max overload power, reducing cost of
transformer, primary clamp & secondary components
• ON-time extension – extends low line regulation range/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
• SOURCE pins are electrically quiet for low EMI
Enhanced Safety and Reliability Features
• Accurate hysteretic thermal shutdown protection with
automatic recovery eliminates need for manual reset
• Improved auto-restart delivers <3% of maximum power in short
circuit and open loop fault conditions
• Output overvoltage shutdown with optional Zener
• Line undervoltage detect threshold set using a single optional
• 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
• Extended creepage between DRAIN and all other pins improves
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
• 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.
HV DC Input
Figure 1. Typical Standby Application.
Output Power Table
230 VAC ± 15%
Table 1. Output Power Table.
1. Minimum continuous power in a typical non-ventilated enclosed adapter
measured at +50 °C ambient. Use of an external heatsink will increase power
2. Minimum peak power capability in any design or minimum continuous power in
an open frame design (see Key Applications Considerations).
3. Packages: P: DIP-8C, G: SMD-8C. See Part Ordering Information.
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.
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 startup 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 I , the device latches off until the
BP/M voltage drops below 4.9 V, during a power down. This
can be used to provide an output overvoltage function with a
Zener connected from the BP/M pin to a bias winding supply.
P Package (DIP-8C)
G Package (SMD-8C)
Figure 3. Pin Conﬁguration.
ENABLE/UNDERVOLTAGE (EN/UV) Pin:
This pin has dual functions: enable input and line undervoltage
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
Rev. I 01/09
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 75 μA and 115 μA.
measured with the oscilloscope triggered at the falling edge of
the DRAIN waveform. The waveform in Figure 4 illustrates the
The EN/UV pin also senses line undervoltage 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 undervoltage function.
SOURCE (S) Pin:
This pin is internally connected to the output MOSFET source for
high voltage power return and control circuit common.
TinySwitch-III Functional Description
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 controller consists of an oscillator, enable circuit (sense and
logic), current limit state machine, 5.85 V regulator, BYPASS/
MULTI-FUNCTION pin undervoltage, overvoltage circuit, and
current limit selection circuitry, over-temperature protection,
current limit circuit, leading edge blanking, and a 700 V power
MOSFET. TinySwitch-III incorporates additional circuitry for line
undervoltage sense, auto-restart, adaptive switching cycle on-
time extension, and frequency jitter. Figure 2 shows the
functional block diagram with the most important features.
The typical oscillator frequency is internally set to an average of
132 kHz. Two signals are generated from the oscillator: the
maximum duty cycle signal (DCMAX) and the clock signal that
indicates the beginning of each cycle.
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
Enable Input and Current Limit State Machine
The enable input circuit at the EN/UV pin consists of a low
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 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,
subsequent changes in the EN/UV pin voltage or current during
the remainder of the cycle are ignored.
The current limit state machine reduces the current limit by
discrete amounts at light loads when TinySwitch-III is likely to
switch in the audible frequency range. The lower current limit
raises the effective switching frequency above the audio range
and reduces the transformer ﬂux density, including the
associated audible noise. The state machine monitors the
sequence of enable events to determine the load condition and
adjusts the current limit level accordingly in discrete amounts.
Under most operating conditions (except when close to no-
load), the low impedance of the source follower keeps the
voltage on 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
The 5.85 V regulator charges the bypass capacitor connected
to the BYPASS pin to 5.85 V by drawing a current from the
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.
In addition, there is a 6.4 V shunt regulator clamping the
BYPASS/MULTI-FUNCTION pin at 6.4 V when current is
provided to the BYPASS/MULTI-FUNCTION pin through an
external resistor. This facilitates powering of TinySwitch-III
externally through a bias winding to decrease the no-load
consumption to well below 50 mW.
Figure 4. Frequency Jitter.
BYPASS/MULTI-FUNCTION Pin Undervoltage
The BYPASS/MULTI-FUNCTION pin undervoltage circuitry
disables the power MOSFET when the BYPASS/MULTI-
FUNCTION pin voltage drops below 4.9 V in steady state
operation. Once the BYPASS/MULTI-FUNCTION pin voltage
drops below 4.9 V in steady state operation, it must rise back to
5.85 V to enable (turn-on) the power MOSFET.
Rev. I 01/09