Power Integrations TNY255P, TNY255G, TNY254P, TNY254G, TNY253G Datasheet

®

TNY253/254/255

TinySwitch® Family

Energy Efficient, Low Power Off-line Switchers

Product Highlights

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 up to 2 W from universal input or 4 W from 115 VAC input

Extremely Energy Efficient

•Consumes only 30/60 mW at 115/230 VAC with no load

•Meets Blue Angel, Energy Star, Energy 2000 and 200mW European cell phone requirements for standby

•Saves $1 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

Description

The TinySwitch family uses a breakthrough design to provide the lowest cost, high efficiency, off-line switcher solution in the 0 to 10 W range. These devices integrate a 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 80 mW at no load, from 265VAC 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

+	+
	DC Output
	–
Wide-Range	TinySwitch
HV DC Input	D
	EN
	BP
	S
–
	PI-2178-022699
Figure 1. Typical Standby Application.

TinySwitch SELECTION GUIDE

			Recommended Range
	ORDER		for Lowest System Cost*
	PART	PACKAGE	230 VAC or	85-265
	NUMBER		115 VAC
				VAC
			w/Doubler
	TNY253P	DIP-8	0-4 W	0-2 W
	TNY253G	SMD-8
	TNY254P	DIP-8	2-5 W	1-4 W
	TNY254G	SMD-8
	TNY255P	DIP-8	4-10 W	3.5-6.5 W
	TNY255G	SMD-8

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 up to 5 W. The TNY253 is identical to TNY254 except for its lower current limit, which reduces output short circuit current for applications under 2.5W. TNY255 uses higher switching rate of 130kHz to deliver up to 10 W from the same low cost EE16 core for applications such as PC standby supply. An EE13 or EF13 core with safety spaced bobbin can be used for applications under 2.5W. 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.

July 2001

TNY253/254/255

BYPASS

50 A

OSCILLATOR

CLOCK

DCMAX

1.5 V + VTH

ENABLE

		REGULATOR			DRAIN
		5.8 V
		UNDER-VOLTAGE
		+	+
	5.8 V	-	-	VI	LIMIT
	5.1 V

THERMAL

SHUTDOWN

S Q

R Q

LEADING

EDGE

BLANKING

SOURCE

PI-2197-061898

Figure 2. Functional Block Diagram.

Pin Functional Description

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 5.8V 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 1.5V with a source current clamp of 50 A.

SOURCE (S) Pin:

Power MOSFET source connection. Primary return.

TinySwitch Functional Description

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, 5.8V Regulator, Under-Voltage

BYPASS			1		8	SOURCE
SOURCE			2		7	SOURCE
SOURCE						SOURCE
			3		6
ENABLE						DRAIN
			4		5

P Package (DIP-8)

G Package (SMD-8)

PI-2199-031501

Figure 3. Pin Configuration.

circuit, Hysteretic Over Temperature Protection, Current Limit circuit, Leading Edge Blanking, and a 700V 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 130kHz). 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 at 1.5V. The input current is clamped by a current source set at 50 A with 10 A hysteresis. The output of the enable sense

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circuit is sampled at the rising edge of the oscillator Clock signal (at the beginning of each cycle). If 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 to 5.8V 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 of 0.1 F 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 5.1V. Once the BYPASS pin voltage drops below 5.1 V, it has to rise back to 5.8V to enable (turn-on) the power MOSFET.

Hysteretic Over Temperature Protection

The thermal shutdown circuitry senses the die junction temperature. The threshold is set at 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.

TinySwitch Operation

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

TNY253/254/255

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 by a TL431 device for improved accuracy.

The ENABLE pin pull-down current threshold is nominally 50 A, but is set to 40 A the instant the threshold is exceeded. This is reset to 50 A when the ENABLE pull-down current drops below the current threshold of 40 A.

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 A), then a switching cycle takes place. If the ENABLE pin is low (greater than 50 A) 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

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TNY253/254/255

VEN

CLOCK

DCMAX

IDRAIN

VDRAIN

PI-2255-061298

Figure 4. TinySwitch Operation at Heavy Load.

percentage of cycles will conduct to support the power consumption of the power supply.

The response time of TinySwitch ON/OFF control scheme is very fast compared to normal PWM control. This provides high line ripple rejection and excellent transient response.

Power Up/Down

TinySwitch requires only a 0.1 F capacitor on the BYPASS pin. Because of the small size of this capacitor, the power-up delay is kept to an absolute minimum, typically 0.3 ms (Figure7). Due to the fast nature of the ON/OFF feedback, there is no overshoot at the power supply output. During power-down, the power MOSFET will switch until the rectified line voltage drops to approximately 12 V. The power MOSFET will then remain off without any glitches (Figure 8).

Bias Winding Eliminated

TinySwitch does not require a bias winding to provide power to the chip. Instead it draws the power directly from the DRAIN pin (see Functional Description above). This has two main benefits. First for a nominal application, this eliminates the cost of an extra bias winding and associated components. Secondly, for charger applications, the current-voltage characteristic often allows the output voltage to fall to low values while still delivering power. This type of application normally requires a forward-bias winding which has many more associated components, none of which are necessary with TinySwitch.

Current Limit Operation

Each switching cycle is terminated when the DRAIN current reaches the current limit of the TinySwitch. For a given primary

VEN

CLOCK

DCMAX

IDRAIN

VDRAIN

PI-2259-061298

Figure 5. TinySwitch Operation at Medium Load.

inductance and input voltage, the duty cycle is constant. However, duty cycle does change inversely with the input voltage providing “voltage feed-forward” advantages: good line ripple rejection and relatively constant power delivery independent of the input voltage.

44 kHz Switching Frequency (TNY253/254)

Switching frequency (with no cycle skipping) is set at 44kHz. This provides several advantages. At higher switching frequencies, the capacitive switching losses are a significant proportion of the power losses in a power supply. At higher frequencies, the preferred snubbing schemes are RCD or diodeZener clamps. However, due to the lower switching frequency of TinySwitch , it is possible to use a simple RC snubber (and even just a capacitor alone in 115VAC applications at powers levels below 4W).

Secondly, a low switching frequency also reduces EMI filtering requirements. At 44kHz, the first, second and third harmonics are all below 150kHz where the EMI limits are not very restrictive. For power levels below 4W it is possible to meet worldwide EMI requirements with only resistive and capacitive filter elements (no inductors or chokes). This significantly reduces EMI filter costs.

Finally, if the application requires stringent noise emissions (such as video applications), then the TNY253/254 will allow more effective use of diode snubbing (and other secondary snubbing techniques). The lower switching frequency allows RC snubbers to be used to reduce noise, without significantly impacting the efficiency of the supply.

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VEN

CLOCK

DCMAX

IDRAIN

VDRAIN

PI-2261-061198

Figure 6. TinySwitch Operation at Light Load.

130 kHz Switching Frequency (TNY255)

The switching frequency (with no cycle skipping) is set at 130kHz. This allows the TNY255 to deliver 10W while still using the same size, low cost transformer (EE16) as used by the TNY253/254 for lower power applications.

BYPASS Pin Capacitor

The BYPASS pin uses a small 0.1 F ceramic capacitor for decoupling the internal power supply of the TinySwitch.

Application Examples

Television Standby

		TNY253/254/255
VIN			PI—2253-062398
			0 V

VDRAIN

0 V

0

.2

.4

.6

.8

1

Time (ms)

Figure 7. TinySwitch Power-Up Timing Diagram.

VIN					-062398
					PI—2251
			12 V
					0 V
VDRAIN
			12 V
					0 V
0	100	200	300	400	500

Time (ms)

Figure 8. TinySwitch Power Down Timing Diagram.

TinySwitch is an ideal solution for low cost, high efficiency standby power supplies used in consumer electronic products such as TVs. Figure9 shows a 7.5 V, 1.3 W flyback circuit that uses TNY253 for implementing a TV standby supply. The circuit operates from the DC high voltage already available from the main power supply. This input voltage can range from 120 to 375VDC depending on the input AC voltage range that the TV is rated for. Capacitor C1 filters the high voltage DC supply, and is necessary only if there is a long trace length from the source of the DC supply to the inputs of the TV standby circuit. The high voltage DC bus is applied to the series combination of the primary winding of T1 and the integrated high voltage MOSFET inside the TNY253. The low operating frequency of the TNY253 (44kHz), allows a low cost snubber circuit C2 and R1 to be used in place of a primary clamp circuit. In addition to limiting the DRAIN turn off voltage spike to a safe value, the RC snubber also reduces radiated video noise by

lowering the dv/dt of the DRAIN waveform, which is critical for video applications such as TV and VCR. On fixed frequency PWM and RCC circuits, use of a snubber will result in an undesirable fixed AC switching loss that is independent of load. The ON/OFF control on the TinySwitch eliminates this problem by scaling the effective switching frequency and therefore, switching loss linearly with load. Thus the efficiency of the supply stays relatively constant down to a fraction of a watt of output loading.

The secondary winding is rectified and filtered by D1 and C4 to create the 7.5V output. L1 and C5 provide additional filtering. The output voltage is determined by the sum of the optocoupler U2 LED forward drop (~ 1 V) and Zener diode VR1 voltage. The resistor R2, maintains a bias current through the Zener to improve its voltage tolerance.

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TNY253/254/255
					D1	L1
					1N4934
				T1		15 µH
					10
+				1			+ 7.5 V
						C4
							C5
						330 µF	47 µF
						10 V	10 V
				4	8		RTN
DC IN	Optional	R1	D	TinySwitch		U2
	C1	100 Ω		EN		SFH615-2
			U1
120-375 VDC	0.01 µF	1/2 W
			TNY253P	BP		R2
	1 kV
			S			1 kΩ
		C2			C3
		56 pF		0.1 µF		VR1
		1 kV				1N5235B
–
					C6
					680 pF
					Y1 Safety

PI-2246-082898

Figure 9. 1.3 W TV Stand-by Circuit using TNY253.

						D2	L1
					T1	SB540	10 µH
			C2	1		10		+ 5 V
		R1				C4	C5
		150 kΩ	4700 pF			2700 µF	220 µF
		1 W	1 kV			6.3 V	10 V	RTN
				4		8
			D1
			1N4937	TinySwitch
	Optional			D
			U1	EN
				BP
240-375	C1		TNY255P			U2	R2
	0.01	µF		S			68 Ω
VDC						LTV817
	1 kV
						C3
						0.1 µF	VR1
							1N5229B
								PI-2242-082898

Figure 10. 10 W PC Stand-by Supply Circuit.

PC Standby

The TNY255 was designed specifically for applications such as PC standby, which require up to 10W of power from 230VAC or 100/115VAC with doubler circuit. The TNY255 operates at 130kHz as opposed to 44kHz for TNY253/254. The higher frequency operation allows the use of a low cost EE16 core transformer up to the 10W level. Figure10 shows a 5V, 10W circuit for such an application. The circuit operates from the high voltage DC supply already available from the main power supply. Capacitor C1 filters the high voltage DC supply, and is necessary only if there is a long trace length from the source of the DC supply to the inputs of the PC standby circuit. The high voltage DC bus is applied to the primary winding of T1 in series

with the integrated high voltage MOSFET inside the TNY255. The diode D1, capacitor C2 and resistor R1 comprise the clamp circuit that limits the turn-off voltage spike on the TinySwitch DRAIN pin to a safe value. The secondary winding is rectified and filtered by D2 and C4 to provide the 5V ouput. Additional filtering is provided by L1 and C5. The output voltage is determined by the sum of the optocoupler U2 LED forward drop (~ 1V) and Zener diode VR1 voltage. The resistor R2, maintains a bias current through the Zener to improve its voltage tolerance.

Cellular Phone Charger

The TinySwitch is well suited for applications that require a

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