MAX1718 Maxim, MAX1718 Datasheet - Page 19

• Manufacturer Part Number: MAX1718
• Description: Notebook CPU Step-Down Controller for Intel Mobile Voltage Positioning IMVP-II
• Manufacturer: Maxim

On the rising edge of ZMODE, during power-up with
ZMODE high or on the falling edge of SUS when
ZMODE is high, the impedances at D0–D4 are sampled
by the impedance decoder to see if a large resistance
is in series with the pin. This is called Impedance
mode. If the voltage level on the pin is a logic low, an
internal switch connects the pin to an internal 26kΩ
pullup for about 4µs to see if the pin voltage can be
forced high (Figure 10). If the pin voltage can be pulled
to a logic high, the impedance is considered high and
so is the Impedance mode logic state. Similarly, if the
voltage level on the pin is a logic high, an internal
switch connects the pin to an internal 8kΩ pulldown to
see if the pin voltage can be forced low. If so, the pin is
high impedance and its Impedance mode logic state is
high. In either sampling condition, if the pin’s logic level
does not change, the pin is determined to be low
impedance and the Impedance mode logic state is low.
A high pin impedance (and logic high) is 100kΩ or
greater, and a low impedance (and logic low) is 1kΩ or
less. The Electrical Characteristics table guaranteed
levels for these impedances are 95kΩ and 1.05kΩ to
allow the use of standard 100kΩ and 1kΩ resistors with
5% tolerance.
There are many ways to use the versatile ZMODE mux.
The preferred method will depend on when and how
the VID DAC codes for the various states are deter-
mined. If the output voltage codes are fixed at PC
board design time, program both codes with a simple
combination of pin-strap connections and series resis-
tors (Figure 11). If the output voltage codes are chosen
during PC board assembly, both codes can be inde-
pendently programmed with resistors (Figure 12). This
Figure 9. Internal Multiplexers Functional Diagram
Notebook CPU Step-Down Controller for Intel
______________________________________________________________________________________
V
ZMODE
CC
POR
SUS
S0
S1
Using the ZMODE Mux
D0
D1
D2
D3
D4
Mobile Voltage Positioning (IMVP - II)
IN
IMPEDANCE
DECODER
1
IN
0
ZMODE MUX
DECODER
S0/S1
SEL
matrix of 10 resistor-footprints can be programmed to
all possible Logic mode and Impedance mode code
combinations with only 5 resistors.
Often the CPU pins provide one set of codes that are
typically used with pullup resistors to provide the Logic
mode VID code, and resistors in series with D0–D4 set
the Impedance mode code. Since some of the CPU’s
VID pins may float, the open-circuit pins can present a
problem for the ZMODE mux’s Impedance mode. For
the Impedance mode to work, any pins intended to be
Table 4. Suspend Mode DAC Codes
OUT
OUT
OPEN
OPEN
OPEN
OPEN
GND
GND
GND
GND
REF
REF
REF
REF
V
V
V
V
S1
CC
CC
CC
CC
1
0
SUS MUX
SEL
OUT
OPEN
OPEN
OPEN
OPEN
GND
GND
GND
GND
REF
V
REF
V
REF
V
REF
V
S0
CC
CC
CC
CC
DAC
OUTPUT VOLTAGE (V)
0.975
0.950
0.925
0.900
0.875
0.850
0.825
0.800
0.775
0.750
0.725
0.700
0.675
0.650
0.625
0.600
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