L6706 datasheet(26/47 Pages) STMICROELECTRONICS

26 / 47 page

Load transient boost technology

L6706

26/47

Doc ID 15698 Rev 2

Load transient boost technology

LTB Technology™ further enhances the performances of dual-edge asynchronous systems

by reducing the system latencies and immediately turning ON the phase to provide the

correct amount of energy to the load.

By properly designing the LTB network, as well as the LTB gain, the undershoot and the

ring-back can be minimized also optimizing the output capacitors count.

LTB Technology™ monitors the output voltage through a dedicated pin (see Figure 11)

detecting Load-Transients with selected dV/dt and turning-on immediately the phase.

It then implements a parallel independent loop that (bypassing error amplifier (E/A)

latencies) reacts to load-transients in very short time (< 150 ns).

LTB Technology™ control loop is reported in Figure 10.

Figure 10.

LTB Technology™ control loop

The LTB detector is able to detect output load transients by coupling the output voltage

through an RLTB - CLTB network. After detecting a load transient, the LTB ramp is reset and

then compared with the COMP pin level. The resulting duty-cycle programmed is then OR-

ed with the PWM signal by-passing the main control loop. The phase will then be turned-on

and the EA latencies results bypassed as well.

Short LTB pin to SGND to disable the LTB Technology™: in this condition the device works

as a dual-edge asynchronous PWM controller.

Sensitivity of the load transient detector and the gain of the LTB ramp can be programmed in

order to control precisely both the undershoot and the ring-back.

●

Detector design. RLTB - CLTB is design according to the output voltage deviation dVOUT

which is desired the controller to be sensitive as follow:

Ref

COMP

VSEN

PWM

ESR

d VCOMP

VOUT

ZF(s)

ZFB(s)

Monitor

RLTB

CLTB

PWM_BOOST

LTB Ramp

LTB

LT Detect

VPROG

GND DROP

RECOVERY

RLTBGAIN

LTBGAIN

LTB

OUT

μA

------------------

LTB

π R

LTB

⋅⋅

-----------------------------------------

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