MAX1544 Datasheet, PDF (25/42 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
Table 5. Suspend Mode DAC Codes
LOWER SUSPEND CODES
UPPER SUSPEND CODES
SUS*
S1
OUTPUT
S0
VOLTAGE
(V)
OUTPUT
SUS*
S1
S0
VOLTAGE
(V)
High
GND
GND
0.675
REF
GND
GND
High
GND
REF
0.700
REF
GND
REF
High
GND
OPEN
0.725
REF
GND
OPEN
High
High
GND
REF
V_CC
GND
0.750
0.775
REF
GND
V_CC
REF
REF
GND
High
REF
REF
0.800
REF
REF
REF
High
REF
OPEN
0.825
REF
REF
OPEN
High
High
REF
OPEN
V_CC
GND
0.850
0.875
REF
REF
V_CC
REF
OPEN
GND
High
OPEN
REF
0.900
REF
OPEN
REF
High
OPEN
OPEN
0.925
REF
OPEN
OPEN
High
High
High
High
High
OPEN
V_CC
V_CC
V_CC
V_CC
V_CC
GND
REF
OPEN
V_CC
0.950
0.975
1.000
1.025
1.050
REF
OPEN
V_CC
REF
V_CC
GND
REF
V_CC
REF
REF
V_CC
OPEN
REF
V_CC
V_CC
*Connect the three-level SUS input to a 2.7V or greater supply (3.3V or V_CC) for an input logic level high.
1.075
1.100
1.125
1.150
1.175
1.200
1.225
1.250
1.275
1.300
1.325
1.350
1.375
1.400
1.425
1.450
where I_CC is provided in the Electrical Characteristics,
f_SW is the switching frequency, and Q_G(LOW) and
Q_G(HIGH) are the MOSFET data sheet’s total gate-charge
specification limits at V_GS = 5V.
V+ and V_DD can be tied together if the input power
source is a fixed 4.5V to 5.5V supply. If the 5V bias
supply is powered up prior to the battery supply, the
enable signal (SHDN going from low to high) must be
delayed until the battery voltage is present to ensure
startup.
Free-Running, Constant-On-Time PWM
Controller with Input Feed Forward
The Quick-PWM control architecture is a pseudofixed-
frequency, constant-on-time, current-mode regulator with
input voltage feed forward (Figure 5). This architecture
relies on the output filter capacitor’s ESR to act as the
current-sense resistor, so the output ripple voltage pro-
vides the PWM ramp signal. The control algorithm is sim-
ple: the high-side switch on-time is determined solely by
a one-shot whose period is inversely proportional to input
voltage, and directly proportional to output voltage or the
difference between the main and secondary inductor
currents (see the On-Time One-Shot (TON) section).
Another one-shot sets a minimum off-time. The on-time
one-shot triggers when the error comparator goes low,
the inductor current of the selected phase is below the
valley current-limit threshold, and the minimum off-time
one-shot times out. The controller maintains 180° out-of-
phase operation by alternately triggering the main and
secondary phases after the error comparator drops
below the output voltage set point.
On-Time One-Shot (TON)
The core of each phase contains a fast, low-jitter,
adjustable one-shot that sets the high-side MOSFETs
on-time. The one-shot for the main phase varies the on-
time in response to the input and feedback voltages.
The main high-side switch on-time is inversely propor-
tional to the input voltage as measured by the V+ input,
and proportional to the feedback voltage (V_FB):
tON(MAIN) = K(VFB + 0.075V)
V_IN
where K is set by the TON pin-strap connection (Table 6)
and 0.075V is an approximation to accommodate the
expected drop across the low-side MOSFET switch.
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