Datasheet

Vout

10 mV/Div

5V/Div

200 mA/Div

1 Ps/DIV

LM26003

SNVS576D –AUGUST 2008–REVISED MARCH 2013

www.ti.com

When load current increases above this limit, the LM26003 is forced back into PWM operation. The sleep mode

threshold varies with frequency, inductance, and duty-cycle as shown in Figure 15.

Figure 15. Sleep Mode Threshold vs Vin Vout = 3.3V

Below the sleep threshold, decreasing load current results in longer sleep cycles, which can be quantified as

shown below:

Dwake = Iload/Isleep (2)

Where Dwake is the percentage of time awake when the load current is below the sleep threshold. Sleep mode

combined with low IQ operation minimizes the input supply current. Input supply current in sleep mode can be

calculated based on the wake duty cycle, as shown below:

Iin = Iq + (I

x Dwake) + (Io x D) (3)

Where I

is the gate drive current, calculated as:

= (9.2 x 10

-9

) x f

And Io is the sum of Iload, Ibias, and current through the feedback resistors.

Because this calculation applies only to sleep mode, use the I

q_Sleep_VB

and I

BIAS_SLEEP

values from the Electrical

Characteristics. If VBIAS is connected to ground, use the same equation with Ibias equal to zero and I

q_Sleep_VDD

FPWM

Pulling the FPWM pin high disables sleep mode and forces the LM26003 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 in Figure 16.

Figure 16. Discontinuous Mode Waveforms 75 mA Load, Vin = 12V

Product Folder Links: LM26003