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TNY378GN Datasheet(PDF) 7 Page - List of Unclassifed Manufacturers |
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TNY378GN Datasheet(HTML) 7 Page - List of Unclassifed Manufacturers |
7 / 22 page Rev. C 09/12 7 TNY375-380 www.powerint.com reduced, and the clock frequency is reduced to half that at the highest current limit level (Figure 8). At very light loads, the current limit will be reduced even further (Figure 9). Only a small percentage of cycles will occur to satisfy the power consumption of the power supply. The response time of the ON/OFF control scheme is very fast compared to PWM control. This provides tight regulation and excellent transient response. Power Up/Down The TinySwitch-PK requires only a 0.1 mF capacitor on the BYPASS/MULTI-FUNCTION pin to operate with standard current limit. Because of its small size, the time to charge this capacitor is kept to an absolute minimum, typically 0.6 ms. The time to charge will vary in proportion to the BYPASS/MULTI- FUNCTION pin capacitor value when selecting different current limits. Due to the high bandwidth of the ON/OFF feedback, there is no overshoot at the power supply output. When an external resistor (4 MW) is connected from the power supply positive DC input to the EN/UV pin, the power MOSFET switching will be delayed during power-up until the DC line voltage exceeds the threshold (100 V). Figures 10 and 11 show the power-up timing waveform in applications with and without an external resistor (4 MW) connected to the EN/UV pin. During power-down, when an external resistor is used, the power MOSFET will switch for 32 ms after the output loses regulation. The power MOSFET will then remain off without any glitches since the undervoltage function prohibits restart when the line voltage is low. Figure 12 illustrates a typical power-down timing waveform. Figure 13 illustrates a very slow power-down timing waveform, as in standby applications. The external resistor (4 MW) is connected to the EN/UV pin in this case to prevent unwanted restarts. With the TNY375 and TNY376, no bias winding is needed to provide power to the chip because it draws the power directly from the DRAIN pin (see Functional Description above). This eliminates the cost of a bias winding and associated components. For the TNY377-380 or for applications that require very low no-load power consumption (50 mW), a resistor from a bias winding to the BYPASS/MULTI-FUNCTION pin can provide the power to the chip. The minimum recommended current supplied is I S2 + IDIS. The BYPASS/MULTI-FUNCTION pin in this case will be clamped at 6.4 V. This method will eliminate the power draw from the DRAIN pin, thereby reducing the no-load power consumption and improving full-load efficiency. Current Limit Operation Each switching cycle is terminated when the DRAIN current reaches the current limit of the device. Current limit operation provides good line ripple rejection and relatively constant power delivery independent of input voltage. BYPASS/MULTI-FUNCTION Pin Capacitor The BYPASS/MULTI-FUNCTION pin can use a ceramic capacitor as small as 0.1 mF for decoupling the internal power supply of the device. A larger capacitor size can be used to adjust the current limit. A 1 mF BP/M pin capacitor will select a lower current limit equal to the standard current limit of the next smaller device, and a 10 mF BP/M pin capacitor will select a higher current limit equal to the standard current limit of the next larger device. The TNY375 and TNY376 MOSFETs do not have the capability to match the current limit of the next larger devices in the family. The current limit is therefore increased to the maximum capability of their respective MOSFETs. The higher current limit level of the TNY380 is set to 1105 mA typical. The smaller current limit of the TNY375 is set to 325 mA. |
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