L6756D datasheet(32/36 Pages) STMICROELECTRONICS

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System control loop compensation

L6756D

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Note:

The introduction of a capacitor (CI) in parallel to RFB significantly speeds-up the transient

response by coupling the output voltage dV/dt on the FB pin so using the error amplifier as a

comparator. The COMP pin will suddenly reacts and, also thanks to the LTB Technology®

control scheme, all the phases can be turned on together to immediately give to the output

the required energy. Typical design considers to start from values in the range of 100pF

validating the effect by bench testing. Additional series resistor (RI) can also be used.

9.2

LTB Technology®

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

by reducing the system latencies and immediately turning ON all the phases to provide the

correct amount of energy to the load. By properly deigning 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 detecting Load-

Transients with selected dV/dt, it cancels the interleaved phase-shift, turning-on

simultaneously all phases. it then implements a parallel, independent loop that reacts to

Load-Transients bypassing E/A latencies.

LTB Technology® control loop is reported in Figure 16.

Figure 16.

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 PWMx signal of each phase by-passing the main control loop. All the phases will

then be turned-on together and the EA latencies results bypassed as well.

L6756D 数据表(PDF) 32 Page - STMicroelectronics