TNY253GN-TL Power Integrations IC AC/DC Converters 2W 85-265 VAC 4W 100/115/230 VAC

Lowest Cost, Low Power Switcher Solution· Lower cost than RCC, discrete PWM and other integrated/hybrid solutions· Cost effective replacement for bulky linear adapters· Lowest component count· Simple ON/OFF control ­ no loop compensation devices· No bias winding ­ simpler, lower cost transformer· Allows simple RC type EMI filter for 2 W from universal input 4 W from 115 VAC input Extremely Energy Efficient· Consumes only at 115/230 VAC with no load· Meets Blue Angel, Energy Star, Energy 2000 and 200 mW European cell phone requirements for standby· Saves to $4 per year in energy costs (at $0.12/kWHr) compared to bulky linear adapters· Ideal for cellular phone chargers, standby power supplies for PC, TV and VCR, utility meters, and cordless phones. High Performance at Low Cost· High voltage powered ­ ideal for charger applications· Very high loop bandwidth provides excellent transient response and fast turn on with practically no overshoot· Current limit operation rejects line frequency ripple· Glitch free output when input is removed· Built-in current limit and thermal protection· 44 kHz operation (TNY253/4) with snubber clamp reduces EMI and video noise in TVs & VCRs· Operates with optocoupler or bias winding feedback

ORDER PART NUMBER TNY255P TNY255G Recommended Range for Lowest System Cost* PACKAGE
Description

The TinySwitch family uses a breakthrough design to provide the lowest cost, high efficiency, off-line switcher solution in the 10 W range. These devices integrate 700 V power MOSFET, oscillator, high voltage switched current source, current limit and thermal shutdown circuitry. They start-up and run on power derived from the DRAIN voltage, eliminating the need for a transformer bias winding and the associated circuitry. And yet, they consume only about at no load, from 265 VAC input. A simple ON/OFF control scheme also eliminates the need for loop compensation. The TNY253 and TNY254 switch at 44 kHz to minimize EMI and to allow a simple snubber clamp to limit DRAIN spike

Table 1. *Please refer to the Key Application Considerations section for details.

voltage. At the same time, they allow use of low cost EE16 core transformers to deliver 5 W. The TNY253 is identical to TNY254 except for its lower current limit, which reduces output short circuit current for applications under W. TNY255 uses higher switching rate of 130 kHz to deliver 10 W from the same low cost EE16 core for applications such as PC standby supply. or EF13 core with safety spaced bobbin can be used for applications under 2.5 W. Absence of a bias winding eliminates the need for taping/ margins in most applications, when triple insulated wire is used for the secondary. This simplifies the transformer construction and reduces cost.

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 internally 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.

circuit, Hysteretic Over Temperature Protection, Current Limit circuit, Leading Edge Blanking, and 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 Maximum Duty Cycle signal (DMAX) 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 oscillator 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 1.5 V. The input current is clamped by a current source set 50 µA with 10 µA hysteresis. The output of the enable sense

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, Under-Voltage

circuit is sampled at the rising edge of the oscillator Clock signal (at the beginning of each cycle). it is high, then the power MOSFET is turned on (enabled) for that cycle, otherwise the power MOSFET remains in the off state (cycle skipped). Since the sampling is done only once at the beginning of each cycle, any subsequent changes at the ENABLE pin during the cycle are ignored. 5.8 V Regulator The 5.8 V regulator charges the bypass capacitor connected to the BYPASS pin V by drawing a current from the voltage on the DRAIN, whenever the MOSFET is off. The BYPASS pin is the internal supply voltage node for the TinySwitch. When the MOSFET is on, the TinySwitch runs off of the energy stored in the bypass capacitor. Extremely low power consumption of the internal circuitry allows the TinySwitch to operate continuously from the current drawn from the DRAIN pin. A bypass capacitor value µF is sufficient for both high frequency de-coupling and energy storage. Under Voltage The under-voltage circuitry disables the power MOSFET when the BYPASS pin voltage drops below 5.1 V. Once the BYPASS pin voltage drops below V, it has to rise back V to enable (turn-on) the power MOSFET. Hysteretic Over Temperature Protection The thermal shutdown circuitry senses the die junction temperature. The threshold is set 135 °C with 70 °C hysteresis. When the junction temperature rises above this threshold (135 °C) the power MOSFET is disabled and remains disabled until the die junction temperature falls by 70 °C, at which point it is re-enabled. Current Limit The current limit circuit senses the current in the power MOSFET. When this current exceeds the internal threshold (ILIMIT), the power MOSFET is turned off for the remainder of that cycle. The leading edge blanking circuit inhibits the current limit comparator for a short time (tLEB) after the power MOSFET is turned on. This leading edge blanking time has been set so that current spikes caused by primary-side capacitance and secondary-side rectifier reverse recovery time will not cause premature termination of the switching pulse. device are constant, the power delivered is proportional to the primary inductance of the transformer and is relatively independent of the input voltage. Therefore, the design of the power supply involves calculating the primary inductance of the transformer for the maximum power required. As long as the TinySwitch device chosen is rated for the power level at the lowest input voltage, the calculated inductance will ramp up the current to the current limit before the DCMAX limit is reached. Enable Function The TinySwitch senses the ENABLE pin to determine whether or not to proceed with the next switch cycle as described earlier. Once a cycle is started TinySwitch always completes the cycle (even when the ENABLE pin changes state half way through the cycle). This operation results in a power supply whose output voltage ripple is determined by the output capacitor, amount of energy per switch cycle and the delay of the ENABLE feedback. The ENABLE signal is generated on the secondary by comparing the power supply output voltage with a reference voltage. The ENABLE signal is high when the power supply output voltage is less than the reference voltage. In a typical implementation, the ENABLE pin is driven by an optocoupler. The collector of the optocoupler transistor is connected to the ENABLE pin and the emitter is connected to the SOURCE pin. The optocoupler LED is connected in series with a Zener across the DC output voltage to be regulated. When the output voltage exceeds the target regulation voltage level (optocoupler diode voltage drop plus Zener voltage), the optocoupler diode will start to conduct, pulling the ENABLE pin low. The Zener could be replaced a TL431 device for improved accuracy. The ENABLE pin pull-down current threshold is nominally 50 µA, but is set 40 µA the instant the threshold is exceeded. This is reset 50 µA when the ENABLE pull-down current drops below the current threshold of 40 µA. ON/OFF Control The internal clock of the TinySwitch runs all the time. At the beginning of each clock cycle the TinySwitch samples the ENABLE pin to decide whether or not to implement a switch cycle. If the ENABLE pin is high 40 µA), then a switching cycle takes place. If the ENABLE pin is low (greater than 50 µA) then no switching cycle occurs, and the ENABLE pin status is sampled again at the start of the subsequent clock cycle. At full load TinySwitch will conduct during the majority of its clock cycles (Figure 4). At loads less than full load, the TinySwitch will “skip” more cycles in order to maintain voltage regulation at the secondary output (Figure 5). At light load or no load, almost all cycles will be skipped (Figure 6). A small

TinySwitch is intended to operate in the current limit mode. When enabled, the oscillator turns the power MOSFET on at the beginning of each cycle. The MOSFET is turned off when the current ramps up to the current limit. The maximum ontime of the MOSFET is limited to DCMAX by the oscillator. Since the current limit and frequency of a given TinySwitch