(

)

-

=

´

´

´

IN

OUT

OUT

LOAD(LL)

X

IN

SW

V

V

V

1

I

2 L

V

f

´

=

£

p ´

´

´

C

C

SW

0

X

OUT

R

C

f

f

2

G L

C

3

Control

Logic

and

Driver

UDG-10198

9

14

13

11

SW

DRVH

DRVL

VDDQSNS

G

8

REFIN

6

VREF

+

1.8 V

R1

R2

TPS51916

VDDQ

Σ

+

PWM

TPS51916

www.ti.com

SLUSAE1D – DECEMBER 2010 – REVISED JUNE 2012

D-CAP2™ Mode Operation

Figure 37 shows simplified model of D-CAP2™ architecture.

Figure 37. Simplified Modulator Using D-CAP2™ Mode

The D-CAP2™ mode in the TPS51916 includes an internal feedback network enabling the use of very low ESR

output capacitor(s) such as multi-layer ceramic capacitors. The role of the internal network is to sense the ripple

where

•

G is gain of the amplifier which amplifies the ripple current information generated by the compensation

circuit

(3)

and 14.6 µs, respectively.

When selecting the capacitor, pay attention to its characteristics. For MLCC use X5R or better dielectric and

consider the derating of the capacitance by both DC bias and AC bias. When derating by DC bias and AC bias

are 80% and 50%, respectively, the effective derating is 40% because 0.8 x 0.5 = 0.4. The capacitance of

specialty polymer capacitors may change depending on the operating frequency. Consult capacitor

manufacturers for specific characteristics.

Light-Load Operation

In auto-skip mode, the TPS51916 SMPS control logic automatically reduces its switching frequency to improve

light-load efficiency. To achieve this intelligence, a zero cross detection comparator is used to prevent negative

inductor current by turning off the low-side MOSFET. Equation 4 shows the boundary load condition of this skip

mode and continuous conduction operation.

(4)

Copyright © 2010–2012, Texas Instruments Incorporated

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