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L6756D
2/3/4 phase buck controller for VR10, VR11.1 and AM2 processor applications
October 2008 Rev 1 1/36
L6756D2/3/4 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 current 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
DescriptionL6756D 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 T echnology® 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
Table 1. Device summary
Contents L6756D2/36
Contents Typical application circuit and block diagram . . . . . . . . . . . . . . . . . . . . 41.1 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Pins description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . 82.1 Pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.1 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Device description and operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Output voltage positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.1 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
Output voltage monitoring and protections . . . . . . . . . . . . . . . . . . . . . 266.1 Overvoltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.2 Feedback disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.3 VR_RDY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.4 Over current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Low power-state management and PSI# . . . . . . . . . . . . . . . . . . . . . . . . 28 Main oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
L6756D Contents
3/36 System control loop compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1 Compensation network guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.2 LTB T echnology ® . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Mechanical data and package dimensions . . . . . . . . . . . . . . . . . . . . . . 34 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Typical application circuit and block diagram L6756D
4/36 Typical application circuit and block diagram
1.1 Application circuit
Figure 1. Typical 4phase application circuit
L6756D Typical application circuit and block diagram
5/36
Figure 2. Typical 3phase application circuit
Typical application circuit and block diagram L6756D
6/36
Figure 3. Typical 2phase application circuit
L6756D Typical application circuit and block diagram
7/36
1.2 Block diagram
Figure 4. Block diagram
Pins description and connection diagrams L6756D
8/36 Pins description and connection diagrams
Figure 5. Pins connection (top view)
2.1 Pin descriptions
Table 2. Pin description
L6756D Pins description and connection diagrams
9/36
Table 2. Pin description (continued)
Pins description and connection diagrams L6756D
10/36
Table 2. Pin description (continued)
L6756D Pins description and connection diagrams
11/36
2.2 Thermal data
Table 3. Thermal data
Electrical specifications L6756D
12/36
3 Electrical specifications
3.1 Absolute maximum ratings
Table 4. Absolute maximum ratings
3.2 Electrical characteristics
Table 5. Electrical characteristics
(VCC = 12 V ± 15 %, TJ = 0 °C to 70 °C unless otherwise specified)
L6756D Electrical specifications
13/36
Table 5. Electrical characteristics (continued)
(VCC = 12 V ± 15 %, TJ = 0 °C to 70 °C unless otherwise specified)
Electrical specifications L6756D
14/36
Table 6. Voltage identification (VID) for Intel VR11.x mode
L6756D Electrical specifications
15/36
Table 6. Voltage identification (VID) for Intel VR11.x mode (continued)
Electrical specifications L6756D
16/36
Table 7. Voltage identifications (VID) for Intel VR10 mode + 6.25 mV
L6756D Electrical specifications
17/36
Table 7. Voltage identifications (VID) for Intel VR10 mode + 6.25 mV (continued)
Electrical specifications L6756D
18/36
Table 8. Gate output connections for phase # definition
