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LM26001B Datasheet(PDF) 11 Page - Texas Instruments |
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LM26001B Datasheet(HTML) 11 Page - Texas Instruments |
11 / 27 page Vout 10 mV/Div VSW 5V/Div IL 200 mA/Div 1 Ps/DIV VIN (V) 20 60 80 100 120 160 10 14 16 20 22 PH 15 PH 22 PH 15 PH 500 kHz 330 kHz 140 40 4 6 8 12 18 LM26001B www.ti.com SNVS491B – MAY 2007 – REVISED APRIL 2013 Figure 17. Sleep Mode Threshold vs Vin Vout = 3.3V FPWM Pulling the FPWM pin high disables sleep mode and forces the LM26001B to always operate in PWM mode. Light load efficiency is reduced in PWM mode, but switching frequency remains stable. The FPWM pin can be connected to the VDD pin to pull it high. In FPWM mode, under light load conditions, the regulator operates in discontinuous conduction mode (DCM) . In discontinuous conduction mode, current through the inductor starts at zero and ramps up to its peak, then ramps down to zero again. Until the next cycle, the inductor current remains at zero. At nominal load currents, in FPWM mode, the device operates in continuous conduction mode, where positive current always flows in the inductor. Typical discontinuous operation waveforms are shown below. Figure 18. Discontinuous Mode Waveforms 75mA Load, Vin = 12V At very light load, in FPWM mode, the LM26001B may enter sleep mode. This is to prevent an over-voltage condition from occurring. However, the FPWM sleep threshold is much lower than in normal operation. ENABLE The LM26001B provides a shutdown function via the EN pin to disable the device when the output voltage does not need to be maintained. EN is an analog level input with typically 120 mV of hysteresis. The device is active when the EN pin is above 1.2V (typical) and in shutdown mode when EN is below this threshold. When EN goes high, the internal VDD regulator turns on and charges the VDD capacitor. When VDD reaches 3.9V (typical), the soft-start pin begins to source current. In shutdown mode, the VDD regulator shuts down and total quiescent current is reduced to 10 µA (typical). Because the EN pin sources 4.5 µA (typical) of pull-up current, this pin can be left open or connected to VIN for always-on operation. When open, EN will be pulled up to VIN. Copyright © 2007–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM26001B |
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