LTC1706I-19 查看數據表（PDF） - Linear Technology
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LTC1706I-19 Datasheet PDF : 8 Pages
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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, RFB1, connected between
SENSE and FB, is typically 15k and is not modified by the
state of the VID program inputs. However, the “bottom”
feedback resistor, RFB2, is modified by the four VID inputs
and is precisely ratioed to RFB1.
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 VSENSE.
Each VID input pin is pulled up by a 40k resistor in series
with a diode connected to VCC. Therefore, it should be
grounded (or driven low) to produce a digital low input. It
can be either floated or connected to VCC to get a digital
high input. The series diode is included to prevent the
input from being damaged or clamped if it is driven higher
than VCC.
LTC1706-19
Table 1. VID Inputs and Corresponding Output Voltage
CODE
VID3
VID2
VID1
VID0
0000
GND
GND
GND
GND
0001
GND
GND
GND
Float
0010
GND
GND
Float
GND
0011
GND
GND
Float
Float
0100
GND
Float
GND
GND
0101
GND
Float
GND
Float
0110
GND
Float
Float
GND
0111
GND
Float
GND
GND
1000
Float
GND
GND
GND
1001
Float
GND
GND
Float
1010
Float
GND
Float
GND
1011
Float
GND
Float
Float
1100
Float
Float
GND
GND
1101
Float
Float
GND
Float
1110
Float
Float
Float
GND
OUTPUT
2.00V
1.95V
1.90V
1.85V
1.80V
1.75V
1.70V
1.65V
1.60V
1.55V
1.50V
1.45V
1.40V
1.35V
1.30V
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, VCC and GND pins should be connected, respec-
tively, with the VOSENSE, VOUT, INTVCC and SGND pins of
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.
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