MAX1515ETG+T Maxim Integrated Products, MAX1515ETG+T Datasheet - Page 19

• Manufacturer Part Number: MAX1515ETG+T
• Description: IC REG DDR LV 24-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1515ETG+T

• Applications: Converter, DDR
• Voltage - Input: 1.3 ~ 3.6 V
• Number Of Outputs: 2
• Voltage - Output: 0.5 ~ 2.7 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

While sourcing current, V
with source load current and the voltage across the
inductor decreases. This causes the frequency to drop.
Conversely, while sinking current, V
decrease with sink load current and the voltage across
the inductor increases. Approximate the change in fre-
quency with the following formula:
where R
(40mΩ typ) and the inductor.
The key inductor parameters must be specified: induc-
tor value (L) and peak current (I
equation includes a constant, denoted as LIR, which is
the ratio of peak-to-peak inductor AC ripple current to
maximum DC load current. A higher value of LIR allows
smaller inductance but results in higher losses and rip-
ple. A good compromise between size and losses is
found at approximately a 25% ripple-current to load-
current ratio (LIR = 0.25), which corresponds to a peak
inductor current 1.125 times the DC load current:
Additionally, the minimum inductance chosen must be
high enough to limit the inductor current during the
high-side switch on-time to less than 1A/µs.
The peak-inductor current at full load is 1.125 x
I
peak current is calculated by:
Choose an inductor with a saturation current at least as
high as the peak-inductor current. The inductor select-
ed should exhibit low losses at the chosen operating
frequency.
The input-filter capacitors reduce peak currents and
noise at the voltage source. Place a low-ESR and low-
ESL 0.1µF capacitor for noise filtering no further than
OUT(MAX)
DROP
I
PEAK
L
MIN
if the above equation is used; otherwise, the
Δf
is the resistance of the internal MOSFETs
PWM
=
≥
I
L
OUT MAX
______________________________________________________________________________________
(
V
=
IN MAX
=
(
I
Input Capacitor Selection
(
OUT MAX
−
V
OUT
I
OUT
CHG
)
(
)
V
+
IN
−
×
×
Inductor Selection
)
V
V
and V
×
OUT
OUT
t
×
OFF
PEAK
R
t
2
OFF
LIR
DROP
CHG
)
×
DISCHG
×
×
). The following
L
t
OFF
1
and V
1
μ
A
s
Low-Voltage, Internal Switch,
increase
DISCHG
Step-Down/DDR Regulator
5mm from IN. Select the bulk input capacitor according
to the RMS input ripple-current requirements and volt-
age rating:
The output filter capacitor affects the output-voltage
ripple, output load-transient response, and feedback-
loop stability. For stable operation, the MAX1515
requires a minimum output ripple voltage of V
1% x V
is calculated by:
Stable operation for source-only applications requires
the correct output filter capacitor. When choosing the
output capacitor, ensure that:
For DDR applications, the output capacitance require-
ment needs to be two times the above requirement.
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.
For applications where the output is subject to violent
load transients, the output capacitor’s size 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 applications without large and fast load transients,
the output capacitor’s size often depends on how much
ESR is needed to maintain an acceptable level of out-
put voltage ripple. The output ripple voltage of a step-
down controller equals the total inductor ripple current
multiplied by the output capacitor’s ESR. Therefore, the
maximum ESR required to meet ripple specifications is:
I
RMS
OUT
=
. The minimum ESR of the output capacitor
C
OUT
I
OUT MAX
R
(
≥
ESR
R
Output Capacitor Selection
ESR
V
ESR
REFIN
)
≤
⎛
⎜
⎜
⎝
I
V
≤
≥
OUT MAX
V
OUT
OUT IN
1
×
V
Δ
%
RIPPLE
(
I
t
OUT MAX
OFF
V
(
×
V
STEP
V
IN
(
)
t
OFF
−
LIR
×
L
V
105μ
OUT
)
F
)
/
⎞
⎟
⎟
⎠
μ
s
RIPPLE
19
≥