5
LTC1706-61
170661f
Table 1. VID Inputs and Corresponding Output Voltage
CODE VID4 VID3 VID2 VID1 VID0 OUTPUT
00000 GND GND GND GND GND 1.550V
00001 GND GND GND GND Float 1.525V
00010 GND GND GND Float GND 1.500V
00011 GND GND GND Float Float 1.475V
00100 GND GND Float GND GND 1.450V
00101 GND GND Float GND Float 1.425V
00110 GND GND Float Float GND 1.400V
00111 GND GND Float Float Float 1.375V
01000 GND Float GND GND GND 1.350V
01001 GND Float GND GND Float 1.325V
01010 GND Float GND Float GND 1.300V
01011 GND Float GND Float Float 1.275V
01100 GND Float Float GND GND 1.250V
01101 GND Float Float GND Float 1.225V
01110 GND Float Float Float GND 1.200V
01111 GND Float Float Float Float 1.175V
10000 Float GND GND GND GND 1.150V
10001 Float GND GND GND Float 1.125V
10010 Float GND GND Float GND 1.100V
10011 Float GND GND Float Float 1.075V
10100 Float GND Float GND GND 1.050V
10101 Float GND Float GND Float 1.025V
10110 Float GND Float Float GND 1.000V
10111 Float GND Float Float Float 0.975V
11000 Float Float GND GND GND 0.950V
11001 Float Float GND GND Float 0.925V
11010 Float Float GND Float GND 0.900V
11011 Float Float GND Float Float 0.875V
11100 Float Float Float GND GND 0.850V
11101 Float Float Float GND Float 0.825V
11110 Float Float Float Float GND 0.800V
11111 Float Float Float Float Float *0.775V
*Represents codes without a defined output (shutdown) voltage as
specified in AMD specifications. The LTC1706-61 interprets these codes
as a valid input and produces an output voltage as follows:
(11111) = 0.775V.
OPERATIO
U
When all five VID inputs are high or floating, such as when
no CPU is present in a system, a regulated 0.775V output
is generated at V
SENSE
.
Each VID
input pin is pulled up by a 40k resistor in series
with a diode connected to V
CC
. Therefore, it should be
grounded (or driven low) to produce a digital low input. It
can either be floated or connected to V
CC
to get a digital
high input. The series diode is included to prevent the
input from being damaged or clamped when it is driven
higher than V
CC
.
Voltage Sensing and Feedback Pins
The FB pin is a high impedance node that requires mini-
mum layout distance to reduce extra loading and
unwanted stray pickup.
When used with the LTC1629-6, the LTC1706-61’s FB,
SENSE, V
CC
and GND pins should be connected, respec-
tively, with the EAIN, V
DIFFOUT
, INTV
CC
and SGND pins of
the LTC1629-6. The result of this application is a precisely
controlled, variable output voltage supply to any low
voltage, high current system such as a powerful personal
computer, workstation or network server.
VID Input Characteristics
The VID inputs should be driven with a maximum V
IL
of
0.4V and a minimum V
IH
of 1.6V. However, the VID input
range is not limited to values less than V
CC
. Because of the
internal diode between V
CC
and the pull-up resistor, the
inputs can go higher than V
CC
without being clamped to
V
CC
or damaging the input.
This allows the LTC1706-61 to be fully logic compatible
and operational over a higher input voltage range (less
than the 7V absolute maximum rating).
When a VID input is grounded, there will be a higher
quiescent current flow from V
CC
because of a resistor from
V
CC
through a series diode to each one of the inputs. This
increase in quiescent current is calculated from:
I
Q
= N(V
CC
– V
DIODE
)/R
PULLUP
N is the number of grounded VID inputs. V
DIODE
is typically
0.6V while R
PULLUP
has a typical pull-up resistance of
40kΩ.
VID Programming
A list of programmed inputs and their corresponding
output voltages is shown in Table 1. Programming is
accomplished by applying the proper voltage (or float
condition) on the five digital VID inputs.
