Vout

10 mV/Div

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

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Product Folder Links: LM26001B