 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT3485-3 Datasheet(PDF) 9 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT3485-3 Datasheet(HTML) 9 Page - Linear Technology |
|
|
9 / 20 page  LT3485-0/LT3485-1/ LT3485-2/LT3485-3 9 34850123fb CHARGE pin low. Only when the final output voltage is reached will the DONE pin go low. Figure 2 shows these various modes in action. When CHARGE is first brought high, charging commences. When CHARGE is brought low during charging, the part goes into shutdown and VOUT no longer rises. When CHARGE is brought high again, charging resumes. When the target VOUT voltage is reached, the DONE pin goes low and charging stops. Finally the CHARGE pin is brought low again so the part enters shutdown and the DONE pin goes high. Both VBAT and VIN have undervoltage lockout (UVLO). When one of these pins goes below its UVLO voltage, the DONE pin goes low. With an insufficient bypass capacitor on VBAT or VIN, the ripple on the pin is likely to activate UVLO and terminate the charge. The applications circuits in the data sheet suggest values adequate for most applications. The LT3485 VMONT pin functions as an output to a microcontroller to communicate the progress of the charge. The VMONT pin starts to function at about 0.2V, which corresponds to 64V with a turns ratio of 10.2. When the VMONT pin is at 1V, the DONE pin goes low and the charging terminates. The pin’s output is only valid when the part is charging. The LT3485 also integrates an IGBT drive. The IGBTPWR pin supplies the power. The IGBT output goes high when IGBTIN goes high and conversely goes low when IGBTIN goes low. While IGBTIN is low, the IGBT drive draws no quiescent current from IGBTPWR. OPERATIO The LT3485-0/LT3485-1/LT3485-2/LT3485-3 are designed to charge photoflash capacitors quickly and efficiently. The operation of the part can be best understood by referring to Figure 1. When the CHARGE pin is first driven high, a one shot sets both SR latches in the correct state. The power NPN device, Q1, turns on and current begins ramping up in the primary of transformer T1. Comparator A1 monitors the switch current and when the peak current reaches 2A (LT3485-3), 1.4A (LT3485-0), 1A (LT3485-2) or 0.7A (LT3485-1), Q1 is turned off. Since T1 is utilized as a flyback transformer, the flyback pulse on the SW pin will cause the output of A3 to be high. The voltage on the SW pin needs to be at least 45mV higher than VBAT for this to happen. During this phase, current is delivered to the photoflash capacitor via the secondary and diode D1. As the second- ary current decreases to zero, the SW pin voltage will begin to collapse. When the SW pin voltage drops to 45mV above VBAT or lower, the output of A3 (DCM Comparator) will go low. This fires a one shot which turns Q1 back on. This cycle will continue to deliver power to the output. Output voltage detection is accomplished via R2, R1, Q2, and comparator A2 (VOUT Comparator). Resistors R1 and R2 are sized so that when the SW voltage is 31.5V above VBAT, the output of A2 goes high which resets the master latch. This disables Q1 and halts power delivery. NPN transistor Q3 is turned on pulling the DONE pin low, indicating that the part has finished charging. Power delivery can only be restarted by toggling the CHARGE pin. The CHARGE pin gives full control of the part to the user. The charging can be halted at any time by bringing the Figure 2. Halting the Charging Cycle with the CHARGE Pin LT3485-2 VIN = 3.6V COUT = 50µF VOUT 100V/DIV VCHARGE 5V/DIV VDONE 5V/DIV 1s/DIV 3485 F02 |
Similar Part No. - LT3485-3 |
|
Similar Description - LT3485-3 |
|
|
|
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 |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
