october 2008 rev 1 1/36 1 L6756D 2/3/4 phase buck controller for vr10, vr11 and vr11.1 processor applications features ltb technology ? enhances load transient response 2 to 4 scalable phase operation dual-edge asynchronous architecture psi# input with programmable strategy imon output flexible driver support 7/8 bit programmable output - vr10/11.1 dac 0.5% output voltage accuracy full-differential curr ent sense across dcr integrated remote sense buffer feedback disconnection protection adjustable oscillator from 100 khz to 1 mhz lsless startup to manage pre-biased output programmable soft-start threshold sensitive enable pin for vtt sensing vfqfpn40 6x6 mm package applications high-current vrm / vrd for desktop / server / workstation cpus graphic cards low-voltage, high-current power supplies high-density dc / dc converters description L6756D is a two-to-four phase controller designed to power intel?s most demanding processors and, most in general, low-voltage, high-current power supplies. the device features ltb technology ? to provide the fastest response to load transients thus minimizing the output filter composition. L6756D embeds selectable dac: output voltage is programmable up to 1.6000 v (intel vr10 and vr11.x dacs) managing dvid transitions with 0.5% output voltage accuracy over line, load and temperature variations. the device assures fast protection against load over current and under / over voltage. feedback disconnection prevents from damaging the load in case of misconnections in the system board. low-side-less start-up allows soft-start over pre- biased output avoiding dangerous current return through the main inductors as well as negative spike at the load side. L6756D is available in vfqfpn 6x6 mm package vfqfpn40 6x6 mm table 1. device summary order code package packing L6756D vfqfpn40 tube L6756D tr vfqfpn40 tape and reel www.st.com www..net
contents L6756D 2/36 contents 1 typical application cir cuit and block diagram . . . . . . . . . . . . . . . . . . . . 4 1.1 application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 pins description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . 8 2.1 pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3 electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1 absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2 electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4 device description and operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5 output voltage positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.1 phase # programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.2 current reading and current sharing loop . . . . . . . . . . . . . . . . . . . . . . . . 21 5.3 output voltage load-line definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 5.4 output voltage offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 5.5 dynamic vid transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 5.6 soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 5.6.1 lsless start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 6 output voltage monitoring an d protections . . . . . . . . . . . . . . . . . . . . . 26 6.1 overvoltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.2 feedback disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.3 vr_rdy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 6.4 over current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7 low power-state management and psi# . . . . . . . . . . . . . . . . . . . . . . . . 28 8 main oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
L6756D contents 3/36 9 system control loop com pensation . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.1 compensation network guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 9.2 ltb technology ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 10 mechanical data and package dimensions . . . . . . . . . . . . . . . . . . . . . . 34 11 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
typical application circuit and block diagram L6756D 4/36 1 typical application circuit and block diagram 1.1 application circuit figure 1. typical 4phase application circuit " / / 4 5 ' ! 4 % 0 ( ! 3 % , ' ! 4 % ( 3 , 3 6 ) . , # ( & # " 5 , + ? ) . # $ % # ' . $ 0 7 - 6 # # , " / / 4 5 ' ! 4 % 0 ( ! 3 % , ' ! 4 % ( 3 , 3 , # ( & # $ % # ' . $ 0 7 - 6 # # , " / / 4 5 ' ! 4 % 0 ( ! 3 % , ' ! 4 % ( 3 , 3 , # ( & # $ % # ' . $ 0 7 - 6 # # , " / / 4 5 ' ! 4 % 0 ( ! 3 % , ' ! 4 % ( 3 , 3 , # ( & # $ % # ' . $ 0 7 - 6 # # , ' ' ' ' $ 2 6 / . # 3 # 3 . # 3 # 3 . # 3 # 3 . # 3 # 3 . , ) . 6 $ 2 0 6 & |