Electronic Components Datasheet Search |
|
VishayCRCW12063243F Datasheet(PDF) 7 Page - Texas Instruments |
|
VishayCRCW12063243F Datasheet(HTML) 7 Page - Texas Instruments |
7 / 16 page FB SW L1 C2 RFB2 VOUT2 R3 SM74301 RFB1 F = VOUT 1.385 x 10 -10 x RT SM74301 www.ti.com SNVS719A – JULY 2011 where • RL = the load resistance (1) In continuous conduction mode, current flows continuously through the inductor and never ramps down to zero. In this mode the operating frequency is greater than the discontinuous mode frequency and remains relatively constant with load and line variations. The approximate continuous mode operating frequency can be calculated as follows: (2) The output voltage (VOUT) is programmed by two external resistors as shown in the Block Diagram. The regulation point can be calculated as follows: VOUT = 2.5 x (RFB1 + RFB2) / RFB1 (3) The SM74301 regulates the output voltage based on ripple voltage at the feedback input, requiring a minimum amount of ESR for the output capacitor C2. A minimum of 25mV to 50mV of ripple voltage at the feedback pin (FB) is required for the SM74301. In cases where the capacitor ESR is too small, additional series resistance may be required (R3 in the Block Diagram). For applications where lower output voltage ripple is required the output can be taken directly from a low ESR output capacitor, as shown in Figure 9. However, R3 slightly degrades the load regulation. Figure 9. Low Ripple Output Configuration Start-Up Regulator (VCC) The high voltage bias regulator is integrated within the SM74301. The input pin (VIN) can be connected directly to line voltages between 6V and 95V, with transient capability to 100V. Referring to the block diagram and the graph of VCC vs VIN, when VIN is between 6V and the bypass threshold (nominally 8.5V), the bypass switch (Q2) is on, and VCC tracks VIN within 100 mV to 150 mV. The bypass switch on-resistance is approximately 100Ω, with inherent current limiting at approximately 100 mA. When VIN is above the bypass threshold Q2 is turned off, and VCC is regulated at 7V. The VCC regulator output current is limited at approximately 9.2 mA. When the SM74301 is shutdown using the RT/SD pin, the VCC bypass switch is shut off regardless of the voltage at VIN. When VIN exceeds the bypass threshold, the time required for Q2 to shut off is approximately 2 - 3 µs. The capacitor at VCC (C3) must be a minimum of 0.47 µF to prevent the voltage at VCC from rising above its absolute maximum rating in response to a step input applied at VIN. C3 must be located as close as possible to the VCC and RTN pins. In applications with a relatively high input voltage, power dissipation in the bias regulator is a concern. An auxiliary voltage of between 7.5V and 14V can be diode connected to the VCC pin to shut off the VCC regulator, thereby reducing internal power dissipation. The current required into the VCC pin is shown in the graph “ICC Current vs. Applied VCC Voltage”. Internally a diode connects VCC to VIN requiring that the auxiliary voltage be less than VIN. The turn-on sequence is shown in Figure 10. During the initial delay (t1) VCC ramps up at a rate determined by its current limit and C3 while internal circuitry stabilizes. When VCC reaches the upper threshold of its under- voltage lock-out (UVLO, typically 5.3V) the buckswitch is enabled. The inductor current increases to the current limit threshold (ILIM) and during t2 VOUT increases as the output capacitor charges up. When VOUT reaches the intended voltage the average inductor current decreases (t3) to the nominal load current (IO). Copyright © 2011, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Links: SM74301 |
Similar Part No. - VishayCRCW12063243F |
|
Similar Description - VishayCRCW12063243F |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |