LTC1709 datasheet(17/28 Pages) LINER

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LTC1709

mon, tightly coupled pair of PC traces. The differential

amplifier corrects for DC drops in both the power and

ground paths. The differential amplifier output signal is

divided down and compared with the internal precision

0.8V voltage reference by the error amplifier.

The differential amplifier can be used in either of two

configurations according to the voltage applied to the

AMPMD pin. The first configuration with the connections

illustrated in the Functional Diagram, utilizes a set of

internal, precision resistors to enable precision instru-

mentation-type measurement of the output voltage. This

configuration is activated when the AMPMD pin is tied to

ground. When the AMPMD pin is tied to INTVCC, the

resistors are disconnected and the amplifier inputs are

made directly available. It can be used for general uses if

the amplifier is not required for true remote sensing. The

amplifier has a 0V to 3V common mode input range

limitation due to the internal switching of its inputs. The

output uses an NPN emitter follower without any internal

pull-down current. A DC resistive load to ground is re-

quired in order to sink current. The output will swing from

0V to 10V (VIN ≥ VDIFFOUT + 2V).

Output Voltage Programming

The output voltage is digitally set to levels between 1.3V

and 3.5V using the voltage identification (VID) logic inputs

VID0 to VID4. The internal 5-bit DAC configured as a

precision resistive voltage divider sets the output voltage

in 100mV or 50mV increments according to Table 1.

The VID codes are engineered to be compatible with Intel

Pentium

® II and Pentium III processor specifications for

output voltages from 1.3V to 3.5V.

The LSB (VID0) represents 50mV or 100mV increments

depending on the MSB. The MSB is VID4.

Between the ATTENOUT pin and ground is a variable

resistor, R1, whose value is controlled by the five VID input

pins (VID0 to VID4). Another resistor, R2, between the

ATTENIN and the ATTENOUT pins completes the resistive

divider. The output voltage is thus set by the ratio of

(R1 + R2) to R1.

APPLICATIO S I FOR ATIO

Table 1. VID Output Voltage Programming

VID4

VID3

VID2

VID1

VID0

VOUT (V)

0000

3.50V

0001

3.40V

0010

3.30V

0011

3.20V

0100

3.10V

0101

3.00V

0110

2.90V

0111

2.80V

1000

2.70V

1001

2.60V

1010

2.50V

1011

2.40V

1100

2.30V

1101

2.20V

1110

2.10V

1111

0000

2.05V

0001

2.00V

0010

1.95V

0011

1.90V

0100

1.85V

0101

1.80V

0110

1.75V

0111

1.70V

1000

1.65V

1001

1.60V

1010

1.55V

1011

1.50V

1100

1.45V

1101

1.40V

1110

1.35V

1111

1.30V

* Represents codes without a defined output voltage as specified in Intel

specifications. The LTC1709 interprets these codes as a valid input and

produces an output voltage as follows: (11111) = 2V

Pentium is a registered trademark of Intel Corporation.

Each VID digital input is pulled up by a 40k resistor in

series with a diode from VBIAS. Therefore, it must be

grounded to get a digital low input, and can be either

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