Time (ms)

Current

Feedback

t

ON

t

V

CS

V

COMP

UDG-10187

V

REF

TPS53317

SLUSAK4

– JUNE 2011

www.ti.com

APPLICATION INFORMATION

Functional Overview

The TPS53317 is a D-CAP+

™ mode adaptive on-time converter. Integrated high-side and low-side FET supports

output current to a maximum of 6-ADC. The converter automatically runs in discontinuous conduction mode

(DCM) to optimize light-load efficiency. Multiple switching frequencies are provided to enable optimization of the

power chain for the cost, size and efficiency requirements of the design (see Table 3).

In adaptive on-time converters, the controller varies the on-time as a function of input and output voltage to

maintain a nearly constant frequency during steady-state conditions. In conventional constant on-time converters,

each cycle begins when the output voltage crosses to a fixed reference level. However, in the TPS53317, the

cycle begins when the current feedback reaches an error voltage level which is the amplified difference between

the reference voltage and the feedback voltage.

PWM Operation

Referring to Figure 3, in steady state, continuous conduction mode, the converter operates in the following way.

senses where the two waveforms cross and triggers the on-time generator.

Figure 3. D-CAP+

™ Mode Basic Waveforms

The current feedback is an amplified and filtered version of the voltage between PGND and SW during low-side

system accuracy and reduce the dependence of circuit performance on layout.

10

Copyright

© 2011, Texas Instruments Incorporated