MAX8720ETX+ Maxim Integrated Products, MAX8720ETX+ Datasheet - Page 24

• Manufacturer Part Number: MAX8720ETX+
• Description: IC CNTRL VID STP DWN 36-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8720ETX+

• Applications: Controller, CPU GPU
• Voltage - Input: 2 ~ 28 V
• Number Of Outputs: 1
• Voltage - Output: 0.28 ~ 1.85 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-TQFN Exposed Pad
• Output Voltage: 0.275 V to 1.85 V
• Input Voltage: 2 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The switching frequency and inductor operating point
determine the inductor value as follows:
For example: I
1.25V, f
Find a low-loss inductor with the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice, although powdered
iron is inexpensive and can work well at 200kHz. The
core must be large enough not to saturate at the peak
inductor current (I
Most inductor manufacturers provide inductors in stan-
dard values, such as 1.0µH, 1.5µH, 2.2µH, 3.3µH, etc.
Also look for nonstandard values, which can provide a
better compromise in LIR across the input voltage
range. If using a swinging inductor (where the no-load
inductance decreases linearly with increasing current),
evaluate the LIR with properly scaled inductance values.
The inductor ripple current also impacts transient-
response performance, especially at low V
ferentials. Low inductor values allow the inductor
current to slew faster, replenishing charge removed
from the output filter capacitors by a sudden load step.
The total output-voltage sag is the sum of the voltage
sag while the inductor is ramping up and the voltage
sag before the next pulse can occur.
where t
Electrical Characteristics) and K is from Table 3.
Dynamically Adjustable 6-Bit VID
Step-Down Controller
24
value also determines the load-current value at
which PFM/PWM switchover occurs.
V
______________________________________________________________________________________
SAG
SW
OFF(MIN)
=
L =
= 300kHz, 30% ripple current or LIR = 0.3
2
C
1 2V × 3 0 0 k H z×1 5A × 0.3
L I
L
I
OUT OUT
PEAK
(
LOAD(MAX)
1.2 5V × ( 1 2V −1.2 5V)
∆
=
LOAD MAX
PEAK
V
is the minimum off-time (see the
IN SW LOAD MAX
V
=
V
f
OUT IN
I
LOAD MAX
):
(




K
I
(
V



= 15A, V
)
(
)
V



IN
Transient Response
K
−
Inductor Selection
(
−
V
V
V
)
IN
OUT
V
OUT



V
1
IN
OUT
+
)
IN
LIR
)
LIR
+
= 0.8 3µH
2

 −

= 12V, V
t
OFF MIN



t
IN
OFF MIN
(
- V
(
OUT
)
OUT



)




dif-
=
The amount of overshoot during a full-load to no-load
transient due to stored inductor energy can be calculat-
ed as:
The minimum current-limit threshold must be great
enough to support the maximum load current when the
current limit is at the minimum tolerance value. The
peak inductor current occurs at I
the ripple current; therefore:
where I
threshold voltage divided by the R
100mV default setting, the minimum current-limit
threshold is 90mV.
Connect ILIM to V
threshold. For an adjustable threshold, connect a resis-
tor-divider from REF to GND, with ILIM connected to the
center tap. The external adjustment range of 0.5V to 2.0V
corresponds to a current-limit threshold of 50mV to
200mV. When adjusting the current limit, use 1% toler-
ance resistors and a 10µA divider current to prevent a
significant increase of errors in the current-limit tolerance.
The output filter capacitor must have low enough equiv-
alent series resistance (ESR) to meet output ripple and
load-transient requirements, yet have high enough ESR
to satisfy stability requirements. The output capaci-
tance must be high enough to absorb the inductor
energy while transitioning from full-load to no-load con-
ditions without tripping the overvoltage fault protection.
When using high-capacitance, low-ESR capacitors (see
the Output-Capacitor Stability Requirements section),
the filter capacitor’s ESR dominates the output voltage
ripple. Thus, the output capacitor’s size depends on
the maximum ESR required to meet the output-voltage-
ripple (V
In CPU V
the output is subject to violent load transients, the out-
put capacitor’s size typically depends on how much
ESR is needed to prevent the output from dipping too
LIMIT(LOW)
RIPPLE(P-P)
CORE
V
RIPPLE P P
I
LIMIT LOW
converters and other applications where
V
SOAR
(
(
CC
) specifications:
equals the minimum current-limit
Output Capacitor Selection
−
for a default 100mV current-limit
)
)
≈
Setting the Current Limit
=
>
(
I
R
∆
LOAD MAX
2
ESR ILOAD MAX
I
LOAD MAX
C
OUT OUT
I
(
(
V
DS(ON)
LOAD(MAX)
)



(
)
1
)
2
−
L
LIR
2
)
of N
LIR



L
plus half
. For the