MAX1831EEE+T Maxim Integrated Products, MAX1831EEE+T Datasheet - Page 10

• Manufacturer Part Number: MAX1831EEE+T
• Description: IC REG STEP DOWN 3A 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX1831EEE+T

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.5V, 2.5V, 3.3V, Adj
• Current - Output: 3A
• Frequency - Switching: 1MHz
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 1.12W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

voltage and ground (Figure 4). Regulation is main-
tained for adjustable output voltages when V
Use 30kΩ for R1. R2 is given by the equation:
where V
The MAX1830/MAX1831 feature a programmable PWM
mode-switching frequency, which is set by the input
and output voltage and the value of R
from TOFF to GND. R
off-time in PWM mode. Use the following equation to
select the off-time according to your desired switching
frequency in PWM mode:
where:
t
V
V
V
power switch
V
synchronous-rectifier switch
f
Select R
Recommended values for R
430kΩ for off-times of 0.4µs to 4µs.
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 current (ripple
current) to maximum DC load current. A higher value of
LIR allows smaller inductance but results in higher loss-
es and ripple. 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 cur-
rent:
3A, 1MHz, Low-Voltage, Step-Down Regulators with
Synchronous Rectification and Internal Switches
10
OFF
PWM
IN
OUT
PMOS
NMOS
= the input voltage
= the programmed off-time
______________________________________________________________________________________
= switching frequency in PWM mode
= the output voltage
t
OFF
R
REF
= the voltage drop across the internal PMOS
= the voltage drop across the internal NMOS
TOFF
TOFF
is typically 1.1V.
=
according to the formula:
= (t
f
R2
PWM
OFF
Programming the Switching
(
=
V
TOFF
IN
(
- 0.07µs) (110kΩ / 1.00µs)
V
R1
IN
Frequency and Off-Time
–



−
sets the PMOS power switch
V
V
V
OUT
OUT
REF
V
TOFF
PMOS
Inductor Selection
−
PEAK
−
range from 36kΩ to
V
+
1
PMOS



TOFF
). The following
V
NMOS
, connected
)
FB
)
= V
REF
.
where:
I
LIR = ratio of peak-to-peak AC inductor current to DC
load current, typically 0.25
The peak-inductor current at full load is 1.125 x 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 you
select should exhibit low losses at your chosen operat-
ing 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 rip-
ple, output load-transient response, and feedback-loop
stability. For stable operation, the MAX1830/MAX1831
require a minimum output ripple voltage of V
✕
The minimum ESR of the output capacitor should be:
Stable operation requires the correct output-filter
capacitor. When choosing the output capacitor, ensure
that:
OUT
V
OUT
= maximum DC load current
.
I
RIPPLE
RIPPLE
I
PEAK
= input RMS current ripple.
C
=
L
OUT
ESR
=
I
LOAD
=
I
OUT
≥
V
>
V
OUT
t
I
OUT
OFF
OUT
1
+
%
V
V
OUT
×
79
×
OUT
Capacitor Selection
×
t
µ
LIR
OFF
t
2
(
OFF
FV
V
L
×
×
IN
V
µ /
IN
L
t
OFF
−
s
V
OUT
RIPPLE
)
OUT
≥ 1%
if