IN

OUT

OUT

OUT(LL)

SW

IN

(V

V

) V

1

I

2 L

V

-

´

=

´

´ ´ ¦

10

TPS565201

SLVSE71 – SEPTEMBER 2017

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Copyright © 2017, Texas Instruments Incorporated

7.3 Feature Description

7.3.1 Adaptive On-Time Control and PWM Operation

The main control loop of the TPS565201 is adaptive on-time pulse width modulation (PWM) controller that

supports a proprietary D-CAP2™ mode control. The D-CAP2™ mode control combines adaptive on-time control

with an internal compensation circuit for pseudo-fixed frequency and low external component count configuration

with low-ESR ceramic output capacitors. It is stable even with virtually no ripple at the output.

At the beginning of each cycle, the high-side MOSFET is turned on. This MOSFET is turned off after internal

hence it is called adaptive on-time control. The one-shot timer is reset and the high-side MOSFET is turned on

again when the feedback voltage falls below the reference voltage. An ripple is added to reference voltage to

7.3.2 Pulse Skip Mode

The TPS565201 is designed with Eco-mode™ to maintain high light load efficiency. As the output current

decreases from heavy load condition, the inductor current is also reduced and eventually comes to point that its

rippled valley touches zero level, which is the boundary between continuous conduction and discontinuous

conduction modes. The rectifying MOSFET is turned off when the zero inductor current is detected. As the load

current further decreases the converter runs into discontinuous conduction mode. The on-time is kept almost the

same as it was in the continuous conduction mode so that it takes longer time to discharge the output capacitor

with smaller load current to the level of the reference voltage. This makes the switching frequency lower,

proportional to the load current, and keeps the light load efficiency high. The transition point to the light load

operation IOUT(LL) current can be calculated in Equation 1.

(1)

7.3.3 Soft Start and Pre-Biased Soft Start

The TPS565201 has an internal 1.0-ms soft-start. When the EN pin becomes high, the internal soft-start function

begins ramping up the reference voltage to the PWM comparator.

If the output capacitor is pre-biased at startup, the device initiates switching and starts ramping up only after the

converter ramps up smoothly into regulation point.