MAX8625A Maxim Integrated Products, MAX8625A Datasheet - Page 12

• Manufacturer Part Number: MAX8625A
• Description: Step-Up/Down DC-DC Converter
• Manufacturer: Maxim Integrated Products

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High-Efficiency, Seamless Transition,
Step-Up/Down DC-DC Converter
The MAX8625A output is nominally fixed at 3.3V.
Connect FB to GND to select the internally fixed-output
voltage. For an adjustable output voltage, connect FB
to the center tap of an external resistor-divider connect-
ed from the output to GND (R1 and R2 in Figure 3).
Select 100kΩ for R2 and calculate R1 using the follow-
ing equation:
where V
ulation voltage. V
Note that the minimum output voltage is limited by the
minimum duty cycle. V
The maximum output current provided by the MAX8625A
circuit depends on the inductor value, switching frequen-
cy, efficiency, and input/output voltage.
Figure 3. Typical Application Circuit (Adjustable Output)
12
______________________________________________________________________________________
Calculating Maximum Output Current
FB
= 1.25V and V
R
1
Applications Information
=
OUT
Selecting the Output Voltage
100
2.7V TO 5.5V
must be between 1.25V and 4V.
OUT
INPUT
k
Ω
SELECTION
C1, C2
OUT
MODE
INPUT
22μF
OFF
×
cannot be below 1.25V.
⎛
⎜
⎝
is the desired output reg-
0.1μF
V
V
OUT
FB
C5
ON
−
1
⎞
⎟
⎠
13
14
6
5
8
IN
IN
SKIP
ON
REF
1
LX1
2
LX1
MAX8625A
3.3μH
U1
L
3
See the Typical Operating Characteristics section for
the Maximum Load Current vs. Input Voltage graph.
The input and output ripple currents are both discontin-
uous in this topology. Therefore, select at least two
22µF ceramic capacitors at the input. Select two 22µF
ceramic output capacitors. For best stability over a
wide temperature range, use X5R or better dielectric.
The recommended inductance range for the
MAX8625A is 3.3µH to 4.7µH. Larger values of L give a
smaller ripple, while smaller L values provide a better
transient response. This is because, for boost and step-
up/down topologies, the crossover frequency is
inversely proportional to the value of L for a given load
and input voltage. The MAX8625A is internally compen-
sated, and therefore, the choice of power components
for stable operation is bounded. A 3.3µH inductor with
2A rating is recommended for the 3.3V fixed output with
0.8A load.
LX2
4
LX2
GND
GND
OUT
OUT
FB
9
10
7
11
12
R1
140kΩ
R2
100kΩ
C3, C4
22μF
OUTPUT
Capacitor Selection
Inductor Selection
3V