SNVA046E January   2002  – December 2021 LM2655

 

  1.   Trademarks
  2. 1Introduction
  3. 2Evaluation Board Design
  4. 3Soft Start
  5. 4LDelay
  6. 5Board Layout
  7. 6Revision History

4 LDelay

A capacitor at Ldelay provides an additional delay in enabling the undervoltage latch after the output voltage has reached 80% of its nominal. The value of the capacitor C_delay is determined by the equation:

Equation 3. T_delay (mS) = C_delay (nF) x .4

200pF is a good start point for this component.

GUID-7403CD43-21FF-487E-9AD2-23FD84C5BBA0-low.png Figure 4-1 Start-Up Waveform
Table 4-1 Parts List
Component Value Description Model Number
COUT 150 µF, 10 V Output Capacitor 595D1570010 (Sprague) (Vishay)
CIN 180 µF/20 V Input Capacitor 595D1870020 (Sprague) (Vishay)
CDELAY 200 pF, 0805 Delay VJ0805Y221KXAA (Vishay)
CBYP 0.1 µF, 0805 Bypass Capacitor VJ0805Y104KXAA (Vishay)
Css 4.7 nF, 0805 Soft start VJ0805Y472KXAA (Vishay)
Q1 3A, 30 V Synchronous N-FET IRF7413 or Si 4874 (International Rectifier or Siliconix)
D1 1A, 30 V (Schottky) Catch Diode MBRS130L (On Semiconductor)
LOUT 15 µH, 3A Power Inductor MIDCOM DUS5121-150
COUT 150 µF, 10V Output Capacitor 595D1570010 (Sprague) (Vishay)
C1COMP 4.7nF, 0805 Compensation Capacitor VJ0805Y472KXAA (Vishay)
C2COMP 100 pF, 0805 Compensation Capacitor VJ0805Y100KXAA (Vishay)
CBOOT 0.1 µF, 50 V, 0805 Bootstrap Capacitor VJ0805Y104KXAA (Vishay)
RCOMP 8.2k, 0805 Compensation Resistor CRCW08058251F (Dale)
RFB1 15k, 0805 Upper Feedback Resistor CRCW08051502F (Dale)
RFB2 10k, 0805 Lower Feedback Resistor CRCW08051002F (Dale)
U1 LM2655 Voltage Regulator LM2655 (Texas Instruments)
GUID-13E08391-E1B4-4B3D-A37E-416C0C1077E6-low.png Figure 4-2 LM2655 Evaluation Board Schematic
GUID-C43AE360-C7B7-4FE4-B6F2-C3FA7DF3F8CC-low.png Figure 4-3 LM2655 Buck Converter (12V to 3.3V, Synchronous)
GUID-4AE5A678-1EE5-452D-AC95-E30A8D1059AE-low.png Figure 4-4 LM2655 Buck Converter (12V to 3.3V, Asynchronous)