FX033Z datasheet(15/32 Pages) TI

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Inductor Current

Output Voltage

PWM

SLEW

CSP - CSN

SLEW - VOUT

REFIN

UDG-13015

tON

(1)

Time

C1)

p ´

TPS51363

www.ti.com

SLUSBB5A – FEBRUARY 2013 – REVISED JUNE 2013

PWM Operation

TPS51363 employs DCAP2 mode operation. It uses an internal phase compensation network (RC1, RC2, CC1, CC2

and gain) to work with very low ESR output capacitors such as multi-layer ceramic capacitor (MLCC). The role of

such network is to sense and scale the current ripple component of the output inductor current information and

then use it in conjunction with the voltage feedback signal to achieve loop stability of the converter.

The transconductance (gM) amplifier and SLEW capacitor (C1) forms an integrator. The output ripple voltage

generated is inversed and averaged by this integrator. The AC information is superimposed onto otherwise DC

information and forms a reference voltage at the input of the PWM comparator. As long as the integrator time

constant is much larger than the inverse of the loop crossover frequency, the AC component is negligible.

where

•

gM is 60 µS

•

f0 is 1/3 or 1/4 of the switching frequency (fSW)

(1)

The voltage difference (VSLEW – VVSNS) is then compared to the G×(CSP-CSN) (see Figure 30) voltage at the

PWM comparator inputs. The PWM comparator creates a SET signal to turn on the high-side MOSFET during

each cycle when the current level falls below the loop demand (see Figure 29).

Figure 29. On-Time Waveforms (1)

(1)

ON time is initiated by (VOUT-SLEW) and (CSP-CSN) crossover

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FX033Z Datasheet(PDF) 15 Page - Texas Instruments