Notebook CPU Step-Down Controller for Intel
-
Mobile Voltage Positioning (IMVP II)
3.15V TO 5.5V
*OPTIONAL
4.7nF
1MΩ
1kΩ
1kΩ
1kΩ
1kΩ
1kΩ
D4
D3
D2
D1
D0
100kΩ
100kΩ
MAX1718
ZMODE
CPU
ZMODE = HIGH = 1.25V
ZMODE = LOW = 1.15V
CPU VID =
01100 → 1.15V
(ZMODE LOW)
ZMODE HIGH
VID = 01010 → 1.25V
*TO REDUCE QUIESCENT CURRENT, 1kΩ PULLUP RESISTORS CAN BE REPLACED BY 1MΩ RESISTORS WITH 4.7nF CAPACATORS IN PARALLEL.
Figure 13. Using the Internal Mux with CPU Driving the Logic-Mode VID Code
At the beginning of an output voltage transition, the
V
− V
NEW
25mV
1
MAX1718 blanks the VGATE output, preventing it from
going low. VGATE remains blanked during the transi-
tion and is re-enabled when the slew-rate controller has
set the internal DAC to the final value and one addition-
al slew-rate clock period has passed. The slew-rate
OLD
≤
×
+ T
DELAY
f
SLEW
✕
where f
= 150kHz 120kΩ / R
, V
is the
OLD
TIME
SLEW
original DAC setting, V
is the new DAC setting, and
clock frequency (set by resistor R ) must be set fast
TIME
NEW
T
ranges from zero to a maximum of 2/f
. See
enough to ensure that the longest required transition is
completed within the allowed 100µs.
DELAY
SLEW
Time Frequency Accuracy in the Electrical Charac-
teristics table for f accuracy.
SLEW
The output voltage transition is performed in 25mV
steps, preceded by a delay and followed by one addi-
tional clock period. The total time for a transition
The practical range of R
is 47kΩ to 470kΩ, corre-
TIME
sponding to 2.6µs to 26µs per 25mV step. Although the
DAC takes discrete 25mV steps, the output filter makes
the transitions relatively smooth. The average inductor
current required to make an output voltage transition is:
depends on R
, the voltage difference, and the
TIME
accuracy of the MAX1718’s slew-rate clock, and is not
dependent on the total output capacitance. The greater
the output capacitance, the higher the surge current
required for the transition. The MAX1718 will automati-
cally control the current to the minimum level required
to complete the transition in the calculated time, as long
as the surge current is less than the current limit set by
ILIM. The transition time is given by:
I ≅ C
✕ 25mV ✕ f
SLEW
L
OUT
Output Overvoltage Protection
The overvoltage protection (OVP) circuit is designed to
protect the CPU against a shorted high-side MOSFET
by drawing high current and blowing the battery fuse.
The output voltage is continuously monitored for over-
22 ______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
