LTC1706-19 LINER [Linear Technology], LTC1706-19 Datasheet - Page 5

• Manufacturer Part Number: LTC1706-19
• Description: VID Voltage Programmer
• Manufacturer: LINER [Linear Technology]

OPERATIO
The LTC1706-19 is a precision resistive divider designed
specifically for use with an entire family of Linear Technol-
ogy Corporation DC/DC switching regulators with 1.19V
internal reference and feedback voltages. The LTC1706-19
produces an output voltage ranging from 1.3V to 2V in
50mV steps by closing the loop between the output
voltage sense and the feedback input of the regulator with
the appropriate resistive divider network.
The “top” feedback resistor, R
SENSE and FB, is typically 15k and is not modified by the
state of the VID program inputs. However, the “bottom”
feedback resistor, R
and is precisely ratioed to R
VID Programming
Programming is accomplished by applying the proper
voltage (or float condition) on the four digital VID inputs.
VID3 is the most significant bit (MSB), and VID0 is the
least significant bit (LSB). When all four inputs are low, or
grounded, the regulator output voltage is set to 2V. Each
increasing binary count is equivalent to a decrease of
50mv in the output voltage. Therefore, to obtain a 1.3V
output, the three MSBs are left floating, or high, while only
the LSB, VID0, is grounded. A list of programmed inputs
and their corresponding output voltages is shown in
Table 1.
When all four VID inputs are high or floating (1111), such
as when no CPU is present in a system, a regulated 1.25V
output is generated at V
Each VID input pin is pulled up by a 40k resistor in series
with a diode connected to V
grounded (or driven low) to produce a digital low input. It
can be either floated or connected to V
high input. The series diode is included to prevent the
input from being damaged or clamped if it is driven higher
than V
CC
.
U
FB2
, is modified by the four VID inputs
SENSE
FB1
CC
.
.
. Therefore, it should be
FB1
, connected between
CC
to get a digital
Table 1. VID Inputs and Corresponding Output Voltage
CODE
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
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 LTC1435A, the LTC1706-19’s FB,
SENSE, V
tively, with the V
the LTC1435A. The result of this application is a precisely
controlled variable voltage supply for any low voltage
system such as a palmtop or a laptop computer.
CC
VID3
GND
GND
GND
GND
GND
GND
GND
GND
Float
Float
Float
Float
Float
Float
Float
and GND pins should be connected, respec-
OSENSE
VID2
GND
GND
GND
GND
Float
Float
Float
Float
GND
GND
GND
GND
Float
Float
Float
, V
OUT
, INTV
VID1
GND
GND
Float
Float
GND
GND
Float
GND
GND
GND
Float
Float
GND
GND
Float
LTC1706-19
CC
and SGND pins of
VID0
Float
Float
Float
Float
Float
Float
GND
GND
GND
GND
GND
GND
GND
GND
GND
OUTPUT
2.00V
1.45V
1.35V
1.30V
1.95V
1.90V
1.85V
1.80V
1.75V
1.70V
1.65V
1.60V
1.55V
1.50V
1.40V
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