LTC1706EMS-85 Linear Technology, LTC1706EMS-85 Datasheet - Page 5

• Manufacturer Part Number: LTC1706EMS-85
• Description: IC VID VOLTAGE PROGRAMMER 10MSOP
• Manufacturer: Linear Technology

Specifications of LTC1706EMS-85

• Applications: VID Voltage Programmer
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 1µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Input: -
• Other names: LTC1706EMS85

OPERATIO
The LTC1706-85 is a precision programmable resistive
divider designed specifically for use with an entire family
of Linear Technology Corporation DC/DC switching regu-
lators with 0.8V internal reference and feedback voltages.
The LTC1706-85 programs an output voltage ranging
from 1.050V to 1.825V in 25mV steps, depending on the
state of the VID input pins. The LTC1706-85 in conjunc-
tion with a Linear Technology DC/DC switching regulator
can be used to create a high performance voltage regu-
lator meeting all the requirements of the Intel VRM 8.5
specification.
Voltage Sensing and Feedback Pins
The LTC1706-85 operates by closing the loop between
the output node and the feedback node of the regulator
with an appropriate resistive divider network. The “top”
feedback resistor, R
FB, is a fixed value of typically 10k. The “bottom” feedback
resistor, R
desired regulator output voltage. Feedback resistors R
and R
provide a highly accurate output voltage.
The FB pin is a sensitive node in the circuit. Care should
be taken to minimize the layout distance between the
LTC1706-85 FB node and the regulator feedback node. In
addition, it is important to keep tight ground connections
between the two chips.
VID Inputs
The desired output voltage is obtained by applying the
proper voltage or float condition to the five digital VID
inputs. Table 1 shows the translation table with each in-
put state and the corresponding regulator output voltage.
This translation is derived from and adheres to the Intel
VRM 8.5 specification.
Each VID input is pulled up by a 40k resistor in series with
a diode connected to V
FB2
are matched and temperature stable in order to
FB2
, is set by the five VID inputs to generate the
U
FB1
CC
, connected between SENSE and
. To produce a digital low a VID
FB1
input should be grounded or driven to a low state. The
VID inputs must be driven with a maximum V
(V
When a VID input is grounded or pulled low with a logic
gate, the power supply current will increase because of
the resistor from V
input. This increase in current is calculated from:
where N is the number of grounded VID inputs. With
typical values of V
= 40k, each grounded V
68 A.
To apply a digital high state the input can be either floated,
connected to V
should be driven with a minimum V
Because of the diode between V
tor, the maximum V
can be driven higher than V
damaged. This allows the LTC1706-85 to be fully logic
compatible and operational over a wide input voltage
range, up to the 7V absolute maximum rating.
When used with the LTC1629 and LTC1929, the
LTC1706-85’s FB, SENSE, V
connected respectively to the EAIN, V
SGND pins of the LTC1629 and LTC1929. The result of this
application is a precisely controlled, multiphase, variable
output voltage supply applicable to any low output voltage
system such as a personal computer, workstation or
network server.
In addition to the LTC1629 and LTC1929, the LTC1706-85
also programs a whole family of LTC DC/DC converters
that have an onboard 0.8V reference. The LTC1628,
LTC1735 and LTC1622 are just a few of the high efficiency
step-down switching regulators that will work equally well
with the LTC1706-85. Contact LTC Marketing for a more
complete listing of compatible DC/DC regulators.
CC
I
Q
= 3.3V).
= N • (V
CC
CC
– V
or driven by a logic gate. The VID inputs
CC
IH
DIODE
CC
= 3.3V, V
is not limited to V
through the series diode to the
IN
)/R
input will sink approximately
CC
PULLUP
CC
DIODE
without being clamped or
and GND pins should be
CC
LTC1706-85
and the pull-up resis-
IH
= 0.6V and R
DIFFOUT
of 2V (V
CC
. The VID inputs
, INTV
CC
IL
= 3.3V).
of 0.8V
PULLUP
CC
170685f
5
and