MAX1544 Datasheet, PDF (22/42 Pages) Maxim Integrated Products – Dual-Phase, Quick-PWM Controller for AMD Hammer CPU Core Power Supplies

Dual-Phase, Quick-PWM Controller for
AMD Hammer CPU Core Power Supplies
SUS
1 LSB PER R_TIME CYCLE
V_DAC
OUTPUT SET BY D0–D4
OUTPUT SET BY SUS AND S0-S1
TIME
CLOCK
VROK
t_SLEW
t_BLANK = 24 CLKS
VROK BLANKING
t_SLEW
t_BLANK = 24 CLKS
VROK BLANKING
Figure 4. Suspend Transition
as the surge current is less than the current limit set by
ILIM. The transition time is given by:
t_SLEW
≈¹
f_SLEW


V_OLD − V_NEW
V_LSB


for V_OUT
rising
t_SLEW
≈¹
f_SLEW


V_OLD − V_NEW
V_LSB


+

2

for
V_OUT
falling
where f_SLEW = 500kHz ✕ 30kΩ / R_TIME, V_OLD is the
original DAC setting, V_NEW is the new DAC setting, and
V_LSB = 25mV is the DAC’s smallest voltage increment.
The additional two clock cycles on the falling edge time
are due to internal synchronization delays. See TIME
Frequency Accuracy in the Electrical Characteristics for
f_SLEW limits.
The practical range of R_TIME is 15kΩ to 150kΩ, corre-
sponding to 1.0µs to 10µs per 25mV step. Although the
DAC takes discrete steps, the output filter makes the
transitions relatively smooth. The average inductor cur-
rent required to make an output voltage transition is:
I_L ≅ C_OUT × V_LSB × f_SLEW
Fault Protection
Output Overvoltage Protection
The MAX1544 features selectable output OVP. Connect
OVP to V_CC to enable the output overvoltage-fault pro-
tection. The OVP circuit is designed to protect the CPU
against a shorted high-side MOSFET by drawing high
current and blowing the battery fuse. The MAX1544
continuously monitors the output for an overvoltage
fault. During normal forced-PWM operation (SKIP =
high), the controller detects an OVP fault if the output
voltage exceeds the set DAC voltage by more than 13%
(min). During pulse-skipping operation (SKIP = REF or
GND), the controller detects an OVP fault if the output
voltage exceeds the fixed 2.0V (typ) threshold. When
the OVP circuit detects an overvoltage fault, it immedi-
ately sets the fault latch and activates the shutdown
sequence.
This action discharges the output filter capacitor and
forces the output to ground. If the condition that caused
the overvoltage (such as a shorted high-side MOSFET)
persists, the battery fuse blows. The controller remains
shut down until the fault latch is cleared by toggling
SHDN or cycling the V_CC power supply below 1V.
To disable the overvoltage protection, connect OVP to
GND. The OVP is also disabled when the controller is in
the no-fault test mode (see the No-Fault Test Mode
section).
22 ______________________________________________________________________________________