MAX1536ETI+ Maxim Integrated Products, MAX1536ETI+ Datasheet - Page 15

• Manufacturer Part Number: MAX1536ETI+
• Description: IC PWM STEP-DN DC-DC CONV 28TQFN
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of MAX1536ETI+

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.7 ~ 5.5 V
• Current - Output: 3.6A
• Frequency - Switching: 1.4MHz
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: *
• Package / Case: 28-TQFN Exposed Pad
• Voltage - Supply: 3 V ~ 5.5 V
• Frequency-max: 1.4MHz
• Duty Cycle: 100%
• Pwm Type: Current Mode
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

V
for R
0.3µs to 4.5µs.
The operating frequency of the MAX1536 in PWM mode
is determined primarily by t
V
where:
V
power switch, I
V
synchronous-rectifier switch, I
As the output current increases, V
increase and the voltage across the inductor decreas-
es. This causes the frequency to drop. Approximate the
change in frequency with the following formula:
where R
(54mΩ, typ).
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:
where:
I
LIR = ratio of peak-to-peak AC inductor current to DC
load current, typically 0.25.
OUT
Down Regulator with Dynamic Output Voltage Control
TOFF
OUT
NMOS
PMOS
Frequency Variation with Output Current
TOFF
= maximum DC load current.
as shown in the following formula:
is typically 1.1V and the recommended values
= the voltage drop across the internal PMOS
= the voltage drop across the internal NMOS
PMOS
range from 30.1kΩ to 499kΩ for off-times of
f
3.6A, 1.4MHz, Low-Voltage, Internal-Switch Step-
PWM
R
is the resistance of the internal MOSFETs
∆f
TOFF
OUT
PWM
=
______________________________________________________________________________________
t
=
OFF
× R
L
= -
(
=
t
OFF
V
PMOS
(
V
V
IN
I
I
OUT
OUT
OUT
IN
V x t
−
-
OFF
-
V
IN
0 07
V
.
OUT
x LIR
x R
x t
.
OUT
PMOS
OFF
(set by R
Inductor Selection
OFF
PMOS
µ
-
s
V
× R
PEAK
)
+
PMOS
1 00
110
NMOS
V
.
NMOS
NMOS
). The following
k
µ
TOFF
Ω
s
)
.
and V
), V
IN
PMOS
, and
The peak-inductor current at full load is 1.125 × I
the above equation is used; otherwise, the 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 capacitor reduces peak currents and
noise at the voltage source. Use a low-ESR and low-
ESL capacitor located no further than 5mm from IN.
Select the input capacitor according to the RMS input
ripple-current requirements and voltage rating:
where I
The output-filter capacitor affects the output-voltage
ripple, output load-transient response, and feedback-
loop stability. For stable operation, the MAX1536
requires a minimum output ripple voltage of V
1% × V
The minimum ESR of the output capacitor is calculated by:
Stable operation requires the correct output-filter capaci-
tor. When choosing the output capacitor, ensure that:
An internal transconductance amplifier fine tunes the
output DC accuracy. A capacitor, C
to V
For stability, choose C
tor value maintains a constant average output voltage,
but slows the loop response to changes in output volt-
age. A smaller capacitor value speeds up the loop
response to changes in output voltage but decreases
stability.
CC
OUT
RIPPLE
compensates the transconductance amplifier.
I
RIPPLE
.
I
PEAK
= input RMS current ripple.
C
=
OUT
I
=
LOAD
ESR
I
OUT
≥
COMP
V
>1%
t
+
OFF
OUT
V
OUT
V
OUT
x
x
2
= 470pF. A larger capaci-
(
Capacitor Selection
Integrator Amplifier
t
V
79
V
OFF
x L
x t
L
IN
IN
µ
1
OFF
-
F x V
µ
V
s
OUT
COMP
1
)
, from COMP
RIPPLE
OUT
15
≥
if