Off-Line Switcher. TNY288D Datasheet
Energy-Efficient, Off-Line Switcher with
Line Compensated Overload Power
Lowest System Cost with Enhanced Flexibility
• 725 V rated MOSFET
• Increases BV de-rating margin
• Line compensated overload power – no additional components
• Dramatically reduces max overload variation over universal input
• ±5% turn on UV threshold: line voltage sense with single external
• 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 adapters/
• Allows optimum TinySwitch-4 choice by swapping devices with no
other circuit redesign
• Tight I2f parameter tolerance reduces system cost
• Maximizes MOSFET and magnetics utilization
• 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 heat sinking 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
• Auto-restart delivers <3% of maximum power in short-circuit and
open loop fault conditions
• Output overvoltage shutdown with optional Zener
• Fast AC reset with optional UV external resistor
• 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 field
EcoSmart™– Extremely Energy Efficient
• Easily meets all global energy efficiency regulations
• No-load <30 mW with bias winding, <150 mW at 265 VAC without
• ON/OFF control provides constant efficiency down to very light loads
– ideal for mandatory CEC regulations and EuP standby requirements
• PC Standby and other auxiliary supplies
• DVD/PVR and other low power set top decoders
• Supplies for appliances, industrial systems, metering, etc
• Chargers/adapters for cell/cordless phones, PDAs, digital cameras,
MP3/portable audio, shavers, etc.
Figure 1. Typical Standby Application.
SO-8C (D Package)
DIP-8C (P Package)
Figure 2. Package Options.
eSOP-12B (K Package)
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 heat sink 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, D: SO-8C, K: eSOP-12B. See Part Ordering Information.
This Product is Covered by Patents and/or Pending Patent Applications.
1.0 V + VT
Figure 3. 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 operation.
BYPASS/MULTI-FUNCTION (BP/M) Pin:
This pin has multiple functions:
• It is the connection point for an external bypass capacitor for the
internally generated 5.85 V supply.
• 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 TNY285-290.
• It provides a shutdown function. When the current into the bypass
pin exceeds ISD, the device latches off until the BP/M voltage
drops below 4.9 V, during a power-down or, when the UV function
is employed with external resistors connected to the BP/UV pin, by
taking the UV/EN pin current below IUV minus the reset hysteresis
(Typ. 18.75 μA). This can be used to provide an output overvolt-
age function with a Zener connected from the BYPASS/MULTI-
FUNCTIONAL pin to a bias winding supply.
D Package (SO-8C)
5 S P Package (DIP-8C)
Exposed Pad (On Bottom)
Internally Connected to
Figure 4. Pin Configuration.
Rev. C 02/15
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 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.
The ENABLE/UNDERVOLTAGE 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-4 detects its absence and disables the line undervoltage
SOURCE (S) Pin:
This pin is internally connected to the output MOSFET source for
high-voltage power return and control circuit common.
TinySwitch-4 Functional Description
TinySwitch-4 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 725 V power MOSFET. TinySwitch-4
incorporates additional circuitry for line undervoltage sense,
auto-restart, adaptive switching cycle on-time extension, and
frequency jitter. Figure 3 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.
Figure 5. Frequency Jitter.
The frequency jitter should be measured with the oscilloscope
triggered at the falling edge of the DRAIN waveform. The waveform
in Figure 5 illustrates the frequency jitter.
Enable Input and Current Limit State Machine
The enable input circuit at the ENABLE/UNDERVOLTAGE 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 ENABLE/UNDER- VOLTAGE 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-4 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 trans-
former 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
Under most operating conditions (except when close to no-load), the
low impedance of the source follower keeps the voltage on the
ENABLE/UNDERVOLTAGE 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-4 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-4 externally through a bias winding
to decrease the no-load consumption to well below 50 mW.
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.
The thermal shutdown circuitry senses the die temperature. The
threshold is typically set at 142 °C with 75 °C hysteresis. When the
die temperature rises above this threshold the power MOSFET is
disabled and remains disabled until the die temperature falls by 75 °C,
at which point it is re-enabled. A large hysteresis of 75 °C (typical) is
provided to prevent over-heating of the PC board due to a continuous
Rev. C 02/15