LM5166 datasheet(17/57 Pages) TI2

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L(nom)

OFF

OUT

DCR

DSON2

OUT

û,

) I

175 R

[k @

[ns]

VREF = 1.223V

1.25A

SLEEP

ACTIVE

SLEEP

ACTIVE

IOUT1

IOUT2

ACTIVE

10mV

VOUT

VIN

SLEEP

ACTIVE

Inductor

Current

Voltage

(internal)

Voltage

1.00A

0.75A

0.50A

LM5166

www.ti.com

SNVSA67B – DECEMBER 2016 – REVISED JUNE 2017

Product Folder Links: LM5166

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Feature Description (continued)

Figure 42. PFM Mode With Modulated ILIM, Output Voltage and Inductor Current Representative

Waveforms

As expected, the choice of mode and switching frequency represents a compromise between conversion

efficiency, quiescent current, and passive component size. Lower switching frequency implies reduced switching

losses (including gate charge losses, transition losses, and so forth) and higher overall efficiency. Higher

switching frequency, on the other hand, implies smaller LC output filter and hence, a more compact design.

Lower inductance also helps transient response and reduces the inductor DCR conduction loss. The ideal

switching frequency in a given application is a tradeoff and thus is determined on a case-by-case basis. It relates

to the input voltage, output voltage, most frequent load current level(s), external component choices, and circuit

size requirement. At light loads, the PFM converter has a relatively longer sleep time interval and thus operates

at lower input quiescent current levels.

7.3.2.2 COT Mode Operation

In COT mode, the LM5166-based converter turns on the high-side MOSFET with constant on-time that adapts to

VIN, as defined by Equation 2, to operate with nearly fixed switching frequency when in continuous conduction

mode (CCM). The high-side MOSFET turns on when the feedback voltage (VFB) falls below the reference

voltage. The regulator control loop maintains a constant output voltage by adjusting the PWM off-time as defined

with Equation 3. For stable operation, the feedback voltage must decrease monotonically in phase with the

inductor current during the off-time as explained in Ripple Generation Methods.

(2)

(3)

Diode emulation mode (DEM) prevents negative inductor current, and pulse skipping maintains high efficiency at

light load currents by decreasing the effective switching frequency. The COT-controlled LM5166 waveforms in

CCM and DEM are shown in Figure 43.

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