MAX1544ETL+ Maxim Integrated Products, MAX1544ETL+ Datasheet - Page 29

• Manufacturer Part Number: MAX1544ETL+
• Description: IC QUICK-PWM DUAL-PHASE 40-TQFN
• Manufacturer: Maxim Integrated Products
• Series: Quick-PWM™r

Specifications of MAX1544ETL+

• Applications: Controller, AMD Hammer
• Voltage - Input: 2 ~ 28 V
• Number Of Outputs: 1
• Voltage - Output: 0.68 ~ 1.55 V
• Operating Temperature: -40°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 40-TQFN Exposed Pad
• Output Voltage: 0.675 V to 1.55 V
• Output Current: 40 A
• Input Voltage: 4 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 100 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

SKIP is a three-level logic input—GND, REF, or high.
This input is intended to be driven by a dedicated
open-drain output with the pullup resistor connected
either to REF (or a resistive divider from V
logic-level high-bias supply (3.3V or greater).
When driven to GND, the multiphase Quick-PWM con-
troller disables the secondary phase (DLS = PGND and
DHS = LXS) and the primary phase uses the automatic
pulse-skipping control scheme. When pulled up to REF,
the controller keeps both phases active and uses the
automatic pulse-skipping control scheme—alternating
between the primary and secondary phases with each
cycle.
In skip mode (SKIP = REF or GND), an inherent automatic
switchover to PFM takes place at light loads (Figure 7). A
comparator that truncates the low-side switch on-time at
the inductor current’s zero crossing affects this
switchover. The zero-crossing comparator senses the
inductor current across the current-sense resistors. Once
V
threshold (see the Electrical Characteristics), the com-
parator forces DL low (Figure 5). This mechanism causes
the threshold between pulse-skipping PFM and nonskip-
ping PWM operation to coincide with the boundary
between continuous and discontinuous inductor-current
operation. The PFM/PWM crossover occurs when the
load current of each phase is equal to 1/2 the peak-to-
peak ripple current, which is a function of the inductor
value (Figure 7). For a battery input range of 7V to 20V,
this threshold is relatively constant, with only a minor
dependence on the input voltage due to the typically low
duty cycles. The total load current at the PFM/PWM
crossover threshold (I
where η
the on-time scale factor (Table 6).
The switching waveforms may appear noisy and asyn-
chronous when light loading activates pulse-skipping
operation, but this is a normal operating condition that
results in high light-load efficiency. Varying the inductor
value makes trade-offs between PFM noise and light-load
efficiency. Generally, low inductor values produce a
broader efficiency vs. load curve, while higher values
result in higher full-load efficiency (assuming that the coil
resistance remains fixed) and less output voltage ripple.
Penalties for using higher inductor values include larger
physical size and degraded load-transient response,
especially at low input voltage levels.
C
_
P
I
LOAD SKIP
- V
TOTAL
C
_
(
N
drops below the zero crossing comparator
is the number of active phases, and K is
)
Automatic Pulse-Skipping Switchover
=
______________________________________________________________________________________
η
AMD Hammer CPU Core Power Supplies
LOAD(SKIP)
TOTAL
Dual-Phase, Quick-PWM Controller for



V
OUT
) is approximately:
L
K






V - V
IN
V
IN
CC
OUT
) or to a



The current-limit circuit employs a unique “valley” cur-
rent-sensing algorithm that uses current-sense resistors
between the current-sense inputs (C_P to C_N) as the
current-sensing elements. If the current-sense signal of
the selected phase is above the current-limit threshold,
the PWM controller does not initiate a new cycle
(Figure 8) until the inductor current of the selected
phase drops below the valley current-limit threshold.
When either phase trips the current limit, both phases
are effectively current limited since the interleaved con-
troller does not initiate a cycle with either phase.
Figure 7. Pulse-Skipping/Discontinuous Crossover Point
Figure 8. “Valley” Current-Limit Threshold Point
0
0
∆i
∆t
ON-TIME
=
V
BATT
- V
L
OUT
I
LIMIT(VALLEY)
TIME
Current-Limit Circuit
TIME
= I
LOAD(MAX)
( )
2 - LIR
I
I
PEAK
2η
LOAD
= I
I
I
I
PEAK
LOAD
LIMIT
PEAK
/2
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