Rainbow-electronics MAX1718 Manual de usuario descargar pdf (Pagina 20)

MAX1718

Notebook CPU Step-Down Controller for Intel

Mobile Voltage Positioning (IMVP

II)

20 ______________________________________________________________________________________

low during Impedance mode must appear to be low

impedance, at least for the 4µs sampling interval.

This can be achieved in several ways, including the fol-

lowing two (Figure 13). By using low-impedance pullup

resistors with the CPU’s VID pins, each pin provides the

low impedance needed for the mux to correctly inter-

pret the Impedance mode setting. Unfortunately, the

low resistances cause several mA quiescent currents

for each of the CPU’s grounded VID pins. This quies-

cent current can be avoided by taking advantage of the

fact that D0–D4 need only appear low impedance

briefly, not necessarily on a continuous DC basis. High-

impedance pullups can be used if they are bypassed

with a large enough capacitance to make them appear

low impedance for the 4µs sampling interval. As noted

in Figure 13, 4.7nF capacitors allow the inputs to

appear low impedance even though they are pulled up

with large-value resistors. Each sampling depletes

some charge from the 4.7nF capacitors. A minimum

26kΩ

26kΩ 26kΩ 26kΩ 26kΩ

8kΩ

100kΩ

8kΩ 8kΩ 8kΩ 8kΩ

3.0V TO 5.5V

100kΩ

+5V

B-DATA

LATCH

GND

MAX1718

Figure 10. Internal Mux Impedance-Mode Data Test and Latch

MAX1718

ZMODE

3.0V TO 5.5V

ZMODE HIGH

VID = 01010

1.25V

ZMODE LOW

VID = 01100

1.15V

100kΩ

ZMODE = HIGH = 1.25V

ZMODE = LOW = 1.15V

Figure 11. Using the Internal Mux with Hard-Wired Logic-Mode

and Impedance-Mode DAC Codes

1 2 ... 15 16 17 18 19 20 21 22 23 24 25 ... 34 35

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