データシートサーチシステム |
|
LM1771 データシート(PDF) 9 Page - Texas Instruments |
|
LM1771 データシート(HTML) 9 Page - Texas Instruments |
9 / 26 page LM1771 www.ti.com SNVS446C – JUNE 2006 – REVISED APRIL 2013 To maintain a set frequency in an application, α is always held constant by varying TON inversely with VIN. The three versions of the LM1771 are identified by the on times at a VIN of 3.3V for consistency. For clarification see the table below: Product ID TON @ 3.3V α (V µs) LM1771S 0.5µs 1.65 LM1771T 1.0µs 3.3 LM1771U 2.0µs 6.6 The variation of TON versus VIN can also be expressed graphically. These graphs can be found in the typical curves section of the datasheet. With α being a constant regardless of the version of the LM1771 used, Equation 6 shows that the only dependent variable remaining is VOUT. Since VOUT will be a constant in any application, the frequency will also remain constant. The switching frequency at which the application runs depends upon the VOUT desired and the LM1771 version chosen. For any VOUT, three frequency options (LM1771 versions) can be selected. This can be seen in the table below. The recommended frequency range of operation is 100kHz to 1000kHz. Timing Options (1) VOUT 500ns 1000ns 2000ns 0.8 485 242 121 1 606 303 152 1.2 727 364 182 1.5 909 455 227 1.8 1091 545 273 2.5 1515 758 379 3.3 2000 1000 500 (1) Switching Frequency (kHz) of LM1771 based on output voltage and timing option. Short-Circuit Protection The LM1771 has an internal short circuit comparator that constantly monitors the feedback node (except during soft-start). If the feedback voltage drops below 0.55V (equivalent to the output voltage dropping below 68% of nominal), the comparator will trip causing the part to latch off. The LM1771 will not resume switching until the input voltage is taken below the UVLO threshold and then brought back into its normal operating range, or the part is disabled then re-enabled through the enable pin. The purpose of this function is to prevent a severe short circuit from causing damage to the application. Due to the fast transient response of the LM1771 a severe short on the output causing the feedback to drop would only occur if the load applied had an effective resistance that approaches the PMOS RDS(ON). Precision Enable The LM1771 features a precision enable circuit. If the voltage on the EN pin is 1.2V or greater, the part is enabled and switching will occur. If the enable voltage falls below 1.2V, the part will be placed into a shutdown state and the drivers will be tri-stated. This allows the LM1771 to be easily sequenced using a resistive divider from the output of another regulator, or the working input voltage range of the LM1771 to be set using a resistive divider on VIN. There is no internal pull-up connected to the EN pin, so an external signal is required to initiate switching. It should be noted that when power is first applied to the LM1771, there is a slight delay before the enable comparator is functional. During this delay, typically on the order of 400 µs, the part will be disabled regardless of the voltage on the EN pin. The falling enable threshold features 50 mV of hysteresis Copyright © 2006–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM1771 |
同様の部品番号 - LM1771_15 |
|
同様の説明 - LM1771_15 |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト 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 |