Rainbow Electronics MAX8760 - Manual (Page 24)

MAX8760
Dual-Phase, Quick-PWM Controller for AMD
Mobile Turion 64 CPU Core Power Supplies
24 ______________________________________________________________________________________
LOWER SUSPEND CODES
SUS S1 S0
OUTPUT
VOLTAGE (V)
HIGH GND GND 0.800
HIGH GND REF 0.775
HIGH GND OPEN 0.750
HIGH GND V CC 0.725
HIGH REF GND 0.700
HIGH REF REF 0.675
HIGH REF OPEN 0.650
HIGH REF V
CC
0.625
HIGH OPEN GND 0.600
HIGH OPEN REF 0.575
HIGH OPEN OPEN 0.550
HIGH OPEN V CC 0.525
HIGH V CC GND 0.500
HIGH V CC REF 0.475
HIGH V CC OPEN 0.450
HIGH V CC V CC 0.425
UPPER SUSPEND CODES
SUS S1 S0
OUTPUT
VOLTAGE (V)
REF GND GND 1.200
REF GND REF 1.175
REF GND OPEN 1.150
REF GND V CC 1.125
REF REF GND 1.100
REF REF REF 1.075
REF REF OPEN 1.050
REF REF V CC 1.025
REF OPEN GND 1.000
REF OPEN REF 0.975
REF OPEN OPEN 0.950
REF OPEN V CC 0.925
REF V CC GND 0.900
REF V CC REF 0.875
REF V CC OPEN 0.850
REF V CC V CC 0.825
Table 5. Suspend Mode DAC Codes
*Connect the tri-level SUS input to a 2.7V or greater supply (3.3V or V CC ) for an input logic level high.
Multiphase Quick-PWM
5V Bias Supply (V
CC
and V
DD
)
The Quick-PWM controller requires an external 5V bias
supply in addition to the battery. Typically, this 5V bias
supply is the notebook’s 95%-efficient 5V system sup-
ply. Keeping the bias supply external to the IC
improves efficiency and eliminates the cost associated
with the 5V linear regulator that would otherwise be
needed to supply the PWM circuit and gate drivers. If
stand-alone capability is needed, the 5V bias supply
can be generated with an external linear regulator.
The 5V bias supply must provide V
CC
(PWM controller)
and V
DD
(gate-drive power), so the maximum current
drawn is:
I BIAS = I CC + f SW (Q G(LOW) + Q G(HIGH) )
where I
CC
is provided in the Electrical Characteristics
table, 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 connected 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-fre-
quency, 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 with a period 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.