Electronic Components Datasheet Search |
|
SC4808B-1MSTRT Datasheet(PDF) 11 Page - Semtech Corporation |
|
SC4808B-1MSTRT Datasheet(HTML) 11 Page - Semtech Corporation |
11 / 28 page 11 2006 Semtech Corp. www.semtech.com SC4808B-1 POWER MANAGEMENT VCC UNDER VOLTAGE LOCK OUT Depending on the application and the voltages available, the SC4808B-1 (UVLO = 4.4V) can be used to provide the VCC undervoltage lock out function to ensure the convert- ers controlled start up. Before the VCC UVLO has been reached, the internal refer- ence, oscillator, OUTA/OUTB drivers, and logic are disabled. LINE UNDER VOLTAGE LOCK OUT The SC4808B-1 also provides a line undervoltage (LUVLO = Vref) function. The LUVLO pin is programmed via an ex- ternal resistor divider connected as shown below. The ac- tual start-up voltage can be calculated by using the equa- tion below: () 33 R 33 R 23 R V V REF Startup + × = R27 15k R24 10k 200p C31 VCC R26 2.2k R28 10 2.2u,16V C26 82p C29 15 REF 0.1u,25V C33 R25 18 R33 10k SYNC U4 SC4808 4 5 3 2 10 1 6 7 8 9 FB REF CS RC LUVLO SYNC GND OUTB OUTA VCC R23 56.2k Vin REFERENCE A 3.125V(SC4808B-1) reference voltage is available that can be used to source a typical current of 5mA to the ex- ternal circuitry. The Vref can be used to provide the oscilla- tor RC network with a regulated bias. Application Information (Cont.) OSCILLATOR The oscillator frequency is set by connecting a RC network as shown below. 0 R27 15k 0 200p C31 VCC R28 10 2.2u,16V C26 REF 0.1u,25V C33 R33 10k SYNC U4 SC4808 4 5 3 2 10 1 6 7 8 9 FB REF CS RC LUVLO SYNC GND OUTB OUTA VCC R23 56.2k Vin The oscillator has a ramp voltage of about Vref/2. The os- cillator frequency is twice the frequency of the OUTA and OUTB gate drive controls. The oscillator capacitor C31 is charged by a current sourced from the Vref through R27. Once the RC pin reaches about Vref/2, the capacitor is discharged internally by the SC4808B-1. It should be noted that larger capacitor val- ues will result in a longer dead time during the down slope of the ramp. The following equation can be used as an approximation of the oscillator frequency and the Dead time: 8 . 0 1 _ × ≅ TOT OSC A OSC C R F 9 . 0 1 _ × ≅ TOT OSC B OSC C R F where: Circuit SC OSC TOT C C C C + + = 4808 pF C SC 22 4808 ≅ 3 10 3 5 . 0 − ⋅ × × ≅ REF OSC deadtime V C T The recommended range of timing resistors is between 10 kohm and 200kohm, range of timing capacitors is between 100pF and 1000pF. Timing resistors less than 10 kohm should be avoided. |
Similar Part No. - SC4808B-1MSTRT |
|
Similar Description - SC4808B-1MSTRT |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | 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 |