MAX1718 Maxim, MAX1718 Datasheet - Page 22

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

At the beginning of an output voltage transition, the
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
clock frequency (set by resistor R
enough to ensure that the longest required transition is
completed within the allowed 100µs.
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
depends on R
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:
Notebook CPU Step-Down Controller for Intel
Mobile Voltage Positioning (IMVP - II)
Figure 13. Using the Internal Mux with CPU Driving the Logic-Mode VID Code
22
______________________________________________________________________________________
*TO REDUCE QUIESCENT CURRENT, 1kΩ PULLUP RESISTORS CAN BE REPLACED BY 1MΩ RESISTORS WITH 4.7nF CAPACATORS IN PARALLEL.
*OPTIONAL
4.7nF
CPU VID =
01100 → 1.15V
(ZMODE LOW)
TIME
CPU
, the voltage difference, and the
1MΩ
TIME
) must be set fast
1kΩ
1kΩ
3.15V TO 5.5V
1kΩ
where f
original DAC setting, V
T
Time Frequency Accuracy in the Electrical Charac-
teristics table for f
The practical range of R
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:
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-
DELAY
1kΩ
≤
1kΩ
VID = 01010 → 1.25V
SLEW
ranges from zero to a maximum of 2/f



f
SLEW
ZMODE HIGH
1
100kΩ
100kΩ
= 150kHz
I
L
×
Output Overvoltage Protection
≅ C
SLEW
V
OLD
OUT
25
NEW
D4
D3
D2
D1
D0
accuracy.
−
mV
✕
TIME
✕
V
NEW
120kΩ / R
25mV
is the new DAC setting, and
is 47kΩ to 470kΩ, corre-
MAX1718

 +

ZMODE
✕
T
f
SLEW
DELAY
TIME
ZMODE = HIGH = 1.25V
ZMODE = LOW = 1.15V
, V
OLD
SLEW
is the
. See