Offline Switcher. TNY176P Datasheet
Energy Efficient, Offline Switcher with Enhanced
Flexibility and Extended Power Range
Lowest System Cost with Enhanced Flexibility
• 650 V rating optimized for non-active PFC applications
• 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-LT 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 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
• 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 <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
• Chargers/adapters for cell/cordless phones, PDAs, digital cameras,
MP3/portable audio, shavers, etc.
• DVD/PVR and other low power set top decoders
• Supplies for appliances, industrial systems, metering, etc.
TinySwitch™-LT incorporates a 650 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.
Figure 1. Typical 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 heat sink will increase
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. See Part Ordering Information.
4. See Key Application Considerations.
1.0 V + VT
CURRENT 4.9 V
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 operation.
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 mF capacitor results
in the standard current limit value. Use of a 1 mF capacitor
results in the current limit being reduced to that of the next
smaller device size. Use of a 10 mF capacitor results in the
current limit being increased to that of the next larger device size
3. 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. 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)
D Package (SO-8C)
Figure 3. Pin Configuration.
Rev. G 08/16
ENABLE (EN) Pin:
The 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 mA and 115 mA.
SOURCE (S) Pin:
This pin is internally connected to the output MOSFET source for
high-voltage power return and control circuit common.
TinySwitch-LT Functional Description
TinySwitch-LT 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 , overvoltage circuit, and current limit selection
circuitry, over-temperature protection, current limit circuit, leading
edge blanking, and a 650 V power MOSFET. TinySwitch-LT incorpo-
rates additional circuitry for auto-restart, adaptive switching cycle
on-time extension, and frequency jitter. Figure 2 shows the func-
tional 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 measured with the oscilloscope triggered
at the falling edge of the DRAIN waveform. The waveform in Figure
4 illustrates the frequency jitter.
Figure 4. Frequency Jitter.
Enable Input and Current Limit State Machine
The enable input circuit at the ENABLE pin consists of a low imped-
ance source follower output set at 1.2 V. The current through the
source follower is limited to 115 mA. 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 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-LT 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 transform-
er 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
Under most operating conditions (except when close to no-load),
the low impedance of the source follower keeps the voltage on the
ENABLE 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-FUNC-
TION 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-LT to operate continuously from current it takes
from the DRAIN pin. A bypass capacitor value of 0.1 mF 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-LT externally through a bias
winding to decrease the no-load consumption to well below 50 mW.
The BYPASS/MULTI-FUNCTION pin 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 fault
Rev. G 08/16