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LM3502SQ-25 Datasheet(PDF) 6 Page - Texas Instruments |
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LM3502SQ-25 Datasheet(HTML) 6 Page - Texas Instruments |
6 / 28 page Driver Logic + - Oscillator Current Sense + - Thermal Shutdown Duty Limit Reference Duty Limit Comparator Fb UVP Comparator OVP Comparator PWM Comparator Light Load Comparator Light Load Reference VIN Sw VOUT1 VOUT2 Fb En2 En1 PGND Cntrl AGND N1 N2 P1 Error Amplifier UVP Reference OVP Reference Current Limit Soft Start 9 15,16 12 10 14 4 7 6 2,3 13 FET Logic + - + - Fb Reference Shutdown Comparator + - + - LM3502 SNVS339A – SEPTEMBER 2005 – REVISED AUGUST 2006 www.ti.com Preliminary Electrical Characteristics (1) (2) (continued) Limits in standard typeface are for TJ = 25°C. Limits in bold typeface apply over the full operating junction temperature range ( −40°C ≤ TJ ≤ +125°C). Unless otherwise specified, VIN = 2.5V. Symbol Parameter Conditions Min Typ Max Units IEn2 En2 Pin Input Bias En2 = 2.5V 7 14 µA Current En2 = 0V 0.1 BLOCK DIAGRAM Figure 4. Block Diagram Detailed Description of Operation The LM3502 utilizes an asynchronous current mode pulse-width-modulation (PWM) control scheme to regulate the feedback voltage over specified load conditions. The DC/DC converter behaves as a controlled current source for white LED applications. The operation can best be understood by referring to the block diagram in Figure 4 for the following operational explanation. At the start of each cycle, the oscillator sets the driver logic and turns on the internal NMOS power device, N1, conducting current through the inductor and reverse biasing the external diode. The white LED current is supplied by the output capacitor when the internal NMOS power device, N1, is turned on. The sum of the error amplifier’s output voltage and an internal voltage ramp are compared with the sensed power NMOS, N1, switch voltage. Once these voltages are equal, the PWM 6 Submit Documentation Feedback Copyright © 2005–2006, Texas Instruments Incorporated Product Folder Links: LM3502 |
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