MAX1920 Maxim, MAX1920 Datasheet - Page 7

• Manufacturer Part Number: MAX1920
• Description: PLASTIC ENCAPSULATED DEVICES
• Manufacturer: Maxim

For nearly all applications, the input capacitor, C
may be as small as 2.2µF ceramic with X5R or X7R
dielectric. The input capacitor filters peak currents and
noise at the voltage source and, therefore, must meet
the input ripple requirements and voltage rating.
Calculate the maximum RMS input current as:
The output capacitor, C
tantalum depending upon the chosen application cir-
cuit (see Figures 1 through 4). Table 3 lists some sug-
gested capacitor suppliers.
For ceramic C
or Figure 2. Calculate the minimum capacitor value as:
Select the next standard value larger than C
The C
for capacitor tolerance. Values much larger than
C
stability, but capacitor size and cost increase.
Figure 2. Typical Application Circuit (MAX1920)
2V TO 5.5V
OUT
INPUT
C
OFF
IN
I
ON
(MIN) always improve transient performance and
IN
OUT
(
RMS
(MIN) calculation already includes a margin
1
2
3
C
)
IN
AGND
SHDN
OUT
OUT
=
I
MAX1920
OUT
(
, use the application circuit of Figure 1
MIN
_______________________________________________________________________________________
(
MAX
)
PGND
=
LX
FB
OUT
2 5 10
)
.
6
5
4
×
Ceramic Output Capacitor
, may be either ceramic or
×
Capacitor Selection
V
OUT IN
−
6
R1
R2
×
(
V
V
V
C
IN
CRITICAL
Low-Voltage, 400mA Step-Down
L
FF
−
V
OUT
OUT
UP TO 400mA
)
OUTPUT
DC-DC Converters in SOT23
C
(MIN).
OUT
IN
,
For tantalum C
3 or Figure 4. With tantalum C
resistance (ESR) of C
bility. Generally, 25mV of ESR-ripple at the feedback
node is sufficient. The simplified calculation is:
Because tantalum capacitors rarely specify minimum
ESR, choose a capacitor with typical ESR that is about
twice as much as ESR
greater than this work, output ripple becomes larger.
For tantalum C
capacitance as:
The 1.25 multiplier is for capacitor tolerance. Select any
standard value larger than C
The MAX1921 has factory preset output voltages of
1.5V, 1.8V, 2.5V, 3V, and 3.3V, while the MAX1920 is
externally adjusted by connecting FB to a resistive volt-
age-divider. When using a ceramic output capacitor,
the feedback network must include a compensation
feed-forward capacitor, C
Figure 3. MAX1921 Application Circuit Using Tantalum Output
Capacitor
2V TO 5.5V
INPUT
C
OFF
IN
C
ON
OUT
(
MIN
1
2
3
ESR
IN
AGND
SHDN
OUT
)
MAX1921
=
COUT
OUT
1 25
Feedback and Compensation
, use the application circuit of Figure
.
, calculate the minimum output
OUT
PGND
(
×
OUT
MIN
LX
ESR
COUT
FF
must be large enough for sta-
Tantalum Output Capacitor
6
5
4
)
.
=
COUT
OUT
OUT
8 0 10
L I
.
(MIN). Although ESRs
×
(MIN).
L
×
, the equivalent series
(
OUT
MIN
−
2
)
(
MAX
×
×
V
V
CRITICAL
OUT
)
UP TO 400mA
OUTPUT
C
OUT
7