Electronic Components Datasheet Search |
|
MAX774ESA Datasheet(PDF) 10 Page - Maxim Integrated Products |
|
MAX774ESA Datasheet(HTML) 10 Page - Maxim Integrated Products |
10 / 16 page With light loads, the MOSFET switches on for one or more cycles and then switches off, much like in tradi- tional PFM converters. To increase light-load efficiency, the current limit for the first two pulses is set to one-half the peak current limit. If those pulses bring the output voltage into regulation, the voltage comparator keeps the MOSFET off, and the current limit remains at one-half the peak current limit. If the output voltage is out of regulation after two consecutive pulses, the current limit for the next pulse will equal the full current limit. With heavy loads, the MOSFET first switches twice at one-half the peak current value. Subsequently, it stays on until the switch current reaches the full current limit, and then turns off. After it is off for 2.3µs, the MOSFET switches on once more, and remains on until the switch current again reaches its limit. This cycle repeats until the output is in regulation. A benefit of this control scheme is that it is highly effi- cient over a wide range of input/output ratios and load currents. Additionally, PFM converters do not operate with constant-frequency switching, and have relaxed stability criterion (unlike PWM converters). As a result, their external components require smaller values. With PFM converters, the output voltage ripple is not concentrated at the oscillator frequency (as it is with PWM converters). So for applications where the ripple frequency is important, the PWM control scheme must be used. However, for many other applications, the smaller capacitors and lower supply current of the PFM control scheme make it the better choice. The output voltage ripple with the MAX774/MAX775/MAX776 can be held quite low. For example, using the circuit of Figure 2, only 100mV of output ripple is produced when generating a -5V at 1A output from a +5V input. Bootstrapped vs. Non-Bootstrapped Operation Figures 2 and 3 are the standard application circuits for bootstrapped mode, and Figure 4 is the circuit for non- bootstrapped mode. Since EXT is powered by OUT, -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ Inverting DC-DC Controllers 10 ______________________________________________________________________________________ MAX774 MAX775 MAX776 OUT V+ SHDN CS FB EXT GND P 7 8 C2 0.1 µF R1 0.07 Ω C1 150 µF 6 5 2 3 1 REF 4 Q1 Si9435 1N5822/ MBR340 L1 22 µH C4 * VIN C3 0.1 µF VOUT * MAX774 = 330 µF, 10V MAX775, MAX776 = 120 µF, 20V PRODUCT MAX774 MAX775 MAX776 OUTPUT VOLTAGE (V) -5 -12 -15 INPUT VOLTAGE (V) 3 to 15 3 to 8 3 to 5 OUTPUT CURRENT (A) 1 0.5 0.4 NOTE: Si9435 HAS VGS OF 20V MAX MAX774 MAX775 MAX776 OUT V+ SHDN CS FB EXT GND P 7 8 R2 R3 0.07 Ω C1 150 µF 6 5 2 3 1 REF 4 Q1 Si9435 1N5822/ MBR340 L1 22 µH C4 * VIN C3 0.1 µF VOUT C2 0.1 µF R1 * MAX774 = 330 µF, 10V MAX775, MAX776 = 120 µF, 20V Figure 2. Bootstrapped Connection Using Fixed Output Voltages Figure 3. Bootstrapped Connection Using External Feedback Resistors Figure 4. Non-Bootstrapped Operation (VIN > 4.5V) MAX774 MAX775 MAX776 OUT V+ SHDN CS FB EXT GND P 7 8 R2 R3 0.07 Ω C1 150 µF 6 5 2 3 1 REF 4 Q1 Si9435 1N5822/ MBR340 L1 22 µH C4 * VIN C3 0.1 µF VOUT C2 0.1 µF R1 * MAX774 = 330 µF, 10V MAX775, MAX776 = 120 µF, 20V |
Similar Part No. - MAX774ESA |
|
Similar Description - MAX774ESA |
|
|
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 |