MAX1842EEE Maxim Integrated Products, MAX1842EEE Datasheet - Page 13

• Manufacturer Part Number: MAX1842EEE
• Description: DC/DC Switching Regulators
• Manufacturer: Maxim Integrated Products

Specifications of MAX1842EEE

• Case: ssop
• Dc: 02+
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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 MAX1742/MAX1842
requires a minimum output ripple voltage of V
1% x V
The minimum ESR of the output capacitor should be:
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
A large capacitor value maintains a constant average
output voltage but slows the loop response to changes
in output voltage. A small capacitor value speeds up
the loop response to changes in output voltage but
C
CC
C
OUT
OUT
Synchronous Rectification and Internal Switches
OUT
I
RIPPLE
RIPPLE
compensates the transconductance amplifier.
≥
≥
.
I
PEAK
V
V
t
t
OFF
OUT
OFF
OUT
= input RMS current ripple.
=
ESR
=
______________________________________________________________________________________
I
79
LOAD
33
I
1A/2.7A, 1MHz, Step-Down Regulators with
OUT
μ
μ
>
COMP
FV
FV
+
1
μ /
%
μ /
V
V
s for the MAX
s for the MAX
= 470pF.
OUT
OUT
×
Capacitor Selection
Integrator Amplifier
2
t
OFF
(
L
×
V
×
IN
V
IN
COMP
t
L
OFF
−
V
, from COMP
OUT
1842
1742
)
RIPPLE
OUT
≥
if
decreases stability. Choose the capacitor values that
result in optimal performance.
Soft-start allows a gradual increase of the internal cur-
rent limit to reduce input surge currents at startup and
at exit from shutdown. A timing capacitor, C
from SS to GND sets the rate at which the internal cur-
rent limit is changed. Upon power-up, when the device
comes out of undervoltage lockout (2.6V typ) or after
the SHDN pin is pulled high, a 4µA constant-current
source charges the soft-start capacitor and the voltage
on SS increases. When the voltage on SS is less than
approximately 0.7V, the current limit is set to zero. As
the voltage increases from 0.7V to approximately 1.8V,
the current limit is adjusted from 0 to the current-limit
threshold (see the Electrical Characteristics).The volt-
age across the soft-start capacitor changes with time
according to the equation:
The soft-start current limit varies with the voltage on the
soft-start pin, SS, according to the equation:
where I
Characteristics.
Figure 5. Soft-Start Current Limit over Time
I
LIMIT
V
SS
SHDN
(V)
(A)
LIMIT
0
0
0
SSI
is the current threshold from the Electrical
LIMIT
V
SS
=
V
SS
=
1 1
4μ
−
.
0.7V
C
V
A
0 7
SS
.
×
V
t
×
I
LIMIT
Soft-Start
SS
, placed
t
1.8V
I
LIMIT
13