TNY277PN IC

Technical Specifications of TNY277PN

Datasheet	TNY277PN datasheet
Category	Integrated Circuits (ICs)
Family	PMIC – AC DC Converters, Offline Switchers
Manufacturer	Power Integrations
Series	TinySwitch?-III
Packaging	Tube
Part Status	Active
Output Isolation	Isolated
Internal Switch(s)	Yes
Voltage – Breakdown	700V
Topology	Flyback
Voltage – Start Up	–
Voltage – Supply (Vcc/Vdd)	–
Duty Cycle	65%
Frequency – Switching	132kHz
Power (Watts)	23.5W
Fault Protection	Current Limiting, Open Loop, Over Temperature, Over Voltage, Short Circuit
Control Features	EN
Operating Temperature	-40°C ~ 150°C (TJ)
Package / Case	8-DIP (0.300″, 7.62mm), 7 Leads
Supplier Device Package	DIP-8C
Mounting Type	Through Hole

TNY277PN Description

The TinySwitchTM-III has a 700 V power MOSFET, an oscillator-switched current source at high voltage, a current limit (user-selectable), and thermal shutdown. The ON/OFF control technique the IC series uses gives designers a flexible, affordable, and power-efficient choice.

Product Highlights

• Maximum System Flexibility at the Lowest Possible Price.
• Simple on/off switch with no compensating loops required.
• The limiting current can be adjusted by changing the BP/M capacitor value.
• Peak power, or maximum continuous power in open frame applications, is increased with a higher current limit.
• A lower current limit enhances the efficiency of enclosed adapters and chargers.
• Allows for optimal TinySwitch-III selection by simply switching out components.
• The overall system price benefits from a small margin of error for the I2 f parameter.
• Improves power delivery to MOSFETs and magnetics.
• Transformer, primary clamp, and secondary components costs are minimized as the maximum overload power is reduced.
• The input bulk capacitance can be lowered by increasing the ON time and the low line regulation range/hold-up duration.
• No external biasing is required; the device generates its own bias.
• Lowered EMI filter costs are a direct result of frequency jittering.
• Heatsinking to the PCB is made easier with a pin-out.
• The electrical silence of the SOURCE pins achieves low EMI.

Enhanced Safety and Reliability Features

• There is no longer any need for a manual reset, thanks to the precise hysteretic thermal shutdown protection and automatic recovery.
• The enhanced auto-restart provides 3% maximum power in open-loop and short-circuit fault scenarios.
• Overvoltage protection on the output via a Zener diode.
• The threshold for line undervoltage detection is adjusted with a single optional resistor.
• A reduced number of components improves dependability and makes designing circuit boards with only one side possible.
• Fast on time, little overshoot, and great transient load responsiveness benefit a high bandwidth.
• Creepage between the DRAIN and other pins is lengthened to boost field dependability.

TinySwitch-III Functional Description

TinySwitch-III combines power supply control with a high-voltage power MOSFET switch. It regulates the output voltage with a simple ON/OFF switch rather than a sophisticated PWM (pulse width modulator) algorithm. The controller is equipped with an oscillator, an enable circuit (sense and logic), a current limit state machine, a 5.85 V regulator, circuitry for selecting between undervoltage and overvoltage circuits, a current limit selection circuit, leading edge blanking, overtemperature protection, and a current limit circuit. New features in TinySwitch-III include compensating for frequency jitter, detecting undervoltage on the line, restarting itself, and maintaining power for longer throughout the adaptive switching cycle.

Enable Input and Current Limit State Machine

The EN/UV pin is connected to a 1.2 V low-impedance source follower output, which serves as the enable input circuit. The source follower has a 115 mA current cap. If the current flowing out of this pin exceeds the threshold current, the enable circuit will produce a low logic level (disable) at its output. This state will last until the current flowing out of this pin falls below the threshold current. The output of the enable circuit is sampled once every cycle on the rising edge of the clock. If this signal is high, the power MOSFET will be enabled (turned on) for this cycle. If this value is low, the power MOSFET will not switch on. Changes in the EN/UV pin voltage or current over the remainder of the cycle are disregarded because sampling occurs only at the beginning of each cycle.

The current limit state machine discretely reduces the limit at low loads when TinySwitch-III is designed to switch at audible frequencies. To minimize audible noise from the transformer, a lower current limit elevates the effective switching frequency beyond the auditory range. The load condition is determined by the state machine keeping track of the sequence of enabled events, and discrete amounts change the current limit.

The source follower’s low impedance ensures that the EN/UV pin’s voltage never drops below 1.2 V, even in the disabled state, under normal operating conditions (unless near no-load). The response time of the optocoupler typically linked to this pin is enhanced as a result.

Over Temperature Protection

The circuitry responsible for thermal shutdown monitors the die temperature. In most cases, a 142-degree threshold with a 75-degree hysteresis is used. If the die temperature climbs over this point, the power MOSFET is turned off and stays off until the die temperature drops by 75 °C. To protect the PC board from overheating in the event of a persistent fault state, a significant hysteresis of 75 °C is supplied.

Adaptive Switching Cycle On-Time Extension

Instead of ending the cycle early when the DCMAX signal gets low, the on-time is adaptively extended to stay on until the current limit is achieved. This function lengthens hold-up duration while reducing the bulk capacitor size necessary to sustain regulation at a lower minimum input voltage. Until the power supply’s output stabilizes, the on-time extension is turned off when the power supply is starting up.

Line Undervoltage Sense Circuit

The voltage on the DC line can be monitored by connecting an external resistor from the DC line to the EN/UV pin. The power MOSFET won’t turn on until the EN/UV pin receives more than 25 mA of current during power-up or auto-restart. By connecting the BYPASS/ MULTI-FUNCTION pin to 4.9 V during power up, the line undervoltage condition is maintained.

When the problem with the line having too low of a voltage is fixed, the BYPASS/MULTI-FUNCTION pin goes from 4.9 V to 5.85 V. When the line voltage is too low, the auto-restart counter stops, and the power MOSFET switching is turned off in auto-restart mode. Because of this, the line undervoltage state can’t be fixed in the usual 2.5 seconds. Instead, it takes longer than this to stop the line. When less than 2 mA goes into the EN/UV pin and no external resistor is linked, the line undervoltage circuit can also find it. In this case, the line undervoltage feature is not on.

TinySwitch-III Operation

TinySwitch-III devices use the current limit mode. The power oscillator switches MOSFET on to begin each cycle when turned on. When the current gets up to the current limit or when the DCMAX limit is reached, the MOSFET is turned off. Since the highest current limit level and frequency of a TinySwitch-III design are always the same, the power given to the load is proportional to the primary inductance of the transformer and peak primary current squared.

So, designing the supply requires finding out the main inductance of the transformer based on how much power has to come out. The predicted inductance’s current will ramp up to the current limit before reaching the DCMAX limit if the TinySwitch-III is properly selected for the power level.

Enable Function

TinySwitch-III senses the EN/UV pin to decide whether to start the next switching cycle. The cycle order is used to set the current limit. When a cycle starts, it always finishes it (even if the EN/UV pin condition switches halfway through the cycle). This process makes a power source where the ripple in the output voltage is affected by the output capacitor, the amount of energy used during each switching cycle, and the feedback delay. The EN/UV pin signal on the secondary is made by comparing the power source’s output voltage to a standard value. The EN/UV pin signal is high when the output voltage of the power source is less than the reference voltage.

Conclusion

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