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TNY377PN Datasheet(PDF) 3 Page - Power Integrations, Inc. |
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TNY377PN Datasheet(HTML) 3 Page - Power Integrations, Inc. |
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3 / 20 page  Rev. A 05/07 3 TNY375-380 www.powerint.com 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. The EN/UV 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-PK detects its absence and disables the line under- voltage function. SOURCE (S) Pin: This pin is internally connected to the output MOSFET source for high voltage power return and control circuit common. TinySwitch-PK Functional Description TinySwitch-PK 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 700 V power MOSFET. TinySwitch-PK incorporates additional circuitry for line undervoltage sense, auto-restart, adaptive switching cycle on-time extension, and frequency jitter. Figure 2 shows the functional block diagram with the most important features. Oscillator The typical oscillator frequency is internally set to an average of 264 kHz (at the highest current limit level). Two signals are generated from the oscillator: the maximum duty cycle signal (DC MAX) and the clock signal that indicates the beginning of each cycle. The oscillator incorporates circuitry that introduces a small amount of frequency jitter, typically ±3% of the oscillator frequency, 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 with an oscillator frequency of 264 kHz. Enable Input and Current Limit State Machine The enable input circuit at the EN/UV pin consists of a low impedance 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 EN/UV pin voltage or current during the remainder of the cycle are ignored. When a cycle is disabled, the EN/UV pin is sampled at 264 kHz. This faster sampling enables the power supply to respond faster without being required to wait for completion of the full period. The current limit state machine reduces the current limit by discrete amounts at light loads when TinySwitch-PK 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 transformer 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 amounts. Under most operating conditions (except when close to no- load), the low impedance of the source follower keeps the voltage on the EN/UV 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 the TNY375 and TNY376 to operate continuously from current taken 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-PK externally through a bias winding as required for TNY377-380. Powering the TinySwitch-PK externally in this way also decreases the no-load consumption to below 60 mW. 600 0 2.5 5 272 kHz 256 kHz VDRAIN Time ( µs) 500 400 300 200 100 0 Figure 4. Frequency Jitter. |
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