LINEAR LTC3866 User Guide Manual

Current Mode Switching Supply with Ultralow Inductor DCR Sensing for High Efficiency and High Reliability Jian Li, Haoran Wu and Gina Le

Current mode switching supplies have several advantages over voltage-mode switching supplies: (1) high reliability with fast, cycle-by-cycle current sensing and protection; (2) simple and reliable loop compensation—stable with all ceramic output capacitors; (3) easy and accurate current sharing in high current Poly Phase supplies. In high current applications, power losses in the current sensing component are a concern, so the resistance of the sense component must be as low as possible. The problem is that low resistance sensing elements produce reduced signal-to-noise ratios, such that switching jitter becomes an issue in high current, high density applications.

Figure 1. LTC3866 current sensing

The LTC3866 solves this problem by mak-

scheme with ultralow inductor DCR.

ing it possible to build reliable current VIN VIN

High current paths are shown with

INTVCC

mode switching supplies with <0.5mΩ cur- thicker lines.

BOOST INDUCTOR

rent sensing resistance. This single-phase

LTC3866 DCRL

synchronous buck controller drives all

SW VOUT

RITEMP

N-channel power MOSFET switches with

ITEMP BG

onboard gate drivers. It employs a unique PGND

RS R1 R2 22.6k

architecture that enhances the signal-to-

SNSD+

noise ratio of the current sense signal,

allowing the use of a very low DC resis- RNTC RP

SNSA+

tance (DCR) power inductor or low value SGND

current sensing resistor to maximize

PLACE C1, C2 NEXT TO IC efficiency in high current applications. PLACE R1, R2 NEXT TO INDUCTOR R1C1 = 5 • R2C2

This feature reduces the switching jitter commonly found in low DCR applications.

The controller has a wide 4.5V–38V input

Figure 2. High efficiency, range, remote output voltage sensing with 1.5V/30A step-down converter with very low 100k

accurate 0.5% reference, programmable VIN

FREQ MODE/PLLIN

DCR sensing 4.5V TO 20V

and temperature-compensated current 0.1µF RUN PGOOD 220µF

TK/SS ITEMP

limit when using inductor DCR sens-

ITH EXTVCC

ing, short-circuit soft recovery without

VFB LTC3866 VIN overshoot, and chip thermal shutdown. DIFFOUT INTVCC

DIFFP BOOST

The LTC3866 facilitates the design of high 30.1k DIFFN TG

DCR = 0.32mΩ VOUT

SNSD+ SW 1.5V

efficiency, high power density and high C1 30A

220p F 20k SNS– BG COUT

reliability solutions for telecom sys- 10k PGND

SNSA+

ILIM CLKOUT

tems, industrial and medical instruments, 220n F1.5n F

and DC power distribution systems. The controller is available in a low thermal

24 | April 2012 : LT Journal of Analog Innovation