MAX1544ETL+ Maxim Integrated Products, MAX1544ETL+ Datasheet - Page 32

• 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

The inductor ripple current impacts transient-response
performance, especially at low V
Low inductor values allow the inductor current to slew
faster, replenishing charge removed from the output
filter capacitors by a sudden load step. The amount of
output sag is also a function of the maximum duty fac-
tor, which can be calculated from the on-time and mini-
mum off-time. For a dual-phase controller, the
worst-case output sag voltage can be determined by:
where t
Electrical Characteristics) and K is from Table 6.
The amount of overshoot due to stored inductor energy
can be calculated as:
where η
The minimum current-limit threshold must be high
enough to support the maximum load current when the
current limit is at the minimum tolerance value. The val-
ley of the inductor current occurs at I
half the ripple current; therefore:
where η
I
voltage divided by the current-sense resistor (R
For the 30mV default setting, the minimum current-limit
threshold is 28mV.
Connect ILIM to V
old (see the Electrical Characteristics). In adjustable
mode, the current-limit threshold is precisely 1/20 the
voltage seen at ILIM. For an adjustable threshold, con-
nect a resistive divider from REF to GND with ILIM con-
nected to the center tap. When adjusting the current
limit, use 1% tolerance resistors with approximately
10µA of divider current to prevent a significant increase
of errors in the current-limit tolerance.
Dual-Phase, Quick-PWM Controller for
AMD Hammer CPU Core Power Supplies
32
V
LIMIT(LOW)
SAG
______________________________________________________________________________________
I
LIMIT LOW
=
TOTAL
TOTAL
OFF(MIN)
2
+
C
V
(
∆
equals the minimum current-limit threshold
OUT OUT
SOAR
I
L I
LOAD MAX
(
2
is the total number of active phases.
is the total number of active phases, and
∆
C
V
)
LOAD MAX
OUT
>
CC
(
is the minimum off-time (see the
≈



I
2η
(




for the default current-limit thresh-
LOAD MAX



)
η
(
Setting the Current Limit
(
∆
V
TOTAL
TOTAL



I
IN



)
LOAD MAX
)
V
(
2
OUT
−
V




Transient Response



V
IN
2
V
C
IN
(
V
)
K
OUT
OUT OUT
V



IN
OUT

 +

IN



1
- V
)
K
)
V
)
2
K
−

 +

LOAD(MAX)
t
OUT
OFF MIN

 −

L
LIR
2
t
OFF MIN
(



differentials.
2
t
(
OFF MIN
)



SENSE
(
)




minus
)




).
The output filter capacitor must have low enough effec-
tive series resistance (ESR) to meet output ripple and
load-transient requirements, yet have high enough ESR
to satisfy stability requirements.
In CPU V
the output is subject to large-load transients, the output
capacitor’s size typically depends on how much ESR is
needed to prevent the output from dipping too low
under a load transient. Ignoring the sag due to finite
capacitance:
In non-CPU applications, the output capacitor’s size
often depends on how much ESR is needed to maintain
an acceptable level of output ripple voltage. The output
ripple voltage of a step-down controller equals the total
inductor ripple current multiplied by the output capaci-
tor’s ESR. When operating multiphase systems out-of-
phase, the peak inductor currents of each phase are
staggered, resulting in lower output ripple voltage by
reducing the total inductor ripple current. For 3- or
4-phase operation, the maximum ESR to meet ripple
requirements is:
where η
is the calculated on-time per phase, and t
trigger delay between the master’s DH rising edge and
the slave’s DH rising edge. The trigger delay must be
less than 1/(f
actual capacitance value required relates to the physi-
cal size needed to achieve low ESR, as well as to the
chemistry of the capacitor technology. Thus, the
capacitor is usually selected by ESR and
voltage rating rather than by capacitance value (this is
true of polymer types).
When using low-capacity ceramic filter capacitors,
capacitor size is usually determined by the capacity
needed to prevent V
problems during load transients. Generally, once
enough capacitance is added to meet the overshoot
requirement, undershoot at the rising load edge is no
longer a problem (see the V
in the Transient Response section).
R
ESR
≤
TOTAL
CORE
(
2
V
IN
SW
−
is the total number of active phases, t
converters and other applications where
η
TOTAL OUT ON
R
x η
ESR
Output Capacitor Selection
TOTAL
SAG
≤
V
∆
V
I
RIPPLE
) for stable operation. The
LOAD MAX
and V
)
V
SAG
t
STEP
(
−
L
and V
η
SOAR
TOTAL OUT TRIG
)
SOAR
V
from causing
TRIG
equations
t
is the
ON