MCP1253-ADJI/MS Microchip Technology, MCP1253-ADJI/MS Datasheet - Page 11

• Manufacturer Part Number: MCP1253-ADJI/MS
• Description: IC CHRG PUMP DC/DCCONV ADJ 8MSOP
• Manufacturer: Microchip Technology
• Type: Step-Down (Buck), Step-Up (Boost), Switched Capacitor (Charge Pump)r

Specifications of MCP1253-ADJI/MS

• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.5 ~ 5.5 V
• Current - Output: 120mA
• Frequency - Switching: 1MHz
• Voltage - Input: 2 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Function: Step Up/Step Down
• Output Voltage: 1.5 V to 5.5 V
• Output Current: 120 mA
• Maximum Operating Temperature: + 85 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

5.1
The style and value of capacitors used with the
MCP1252 and MCP1253 family of devices determine
several important parameters such as output voltage
ripple and charge pump strength. To minimize noise
and ripple, it is recommended that low ESR (0.1
capacitors be used for both C
capacitors should be either ceramic or tantalum and
should be 10 µF or higher. Aluminum capacitors are not
recommended because of their high ESR.
If the source impedance to V
megahertz, C
somewhat smaller value of C
the recommended 10 µF, but will not be as effective in
preventing ripple on the V
The value of C
age ripple present on V
C
slower turn-on time from shutdown and a higher in-rush
current.
The flying capacitor (C
charge pump. In order to achieve the maximum rated
output current (120 mA), it is necessary to have at least
1 µF of capacitance for the flying capacitor. A smaller
flying capacitor delivers less charge per clock cycle to
the output capacitor, resulting in lower output ripple.
The output ripple is reduced at the expense of maxi-
mum output current and efficiency.
5.2
The MCP1252-33X50 and MCP1253-33X50 feedback
controllers select between an internally-set, regulated
output voltage (3.3V or 5.0V). Connect SELECT to
GND for a regulated 5.0V output and connect SELECT
to V
The MCP1252-ADJ and MCP1253-ADJ utilize an
external resistor divider that allows the output voltage
to be adjusted between 1.5V and 5.5V. For an adjust-
able output, connect a resistor between V
(R
the following equation, choose R
equal to 30 k
formula:
EQUATION
and
EQUATION
OUT
2002 Microchip Technology Inc.
1
where:
V
V
) and another resistor between FB and GND (R
OUT
FB
IN
for a regulated 3.3V output.
is the internal regulation voltage, nominally 1.21V
will reduce output ripple at the expense of a
is the desired output voltage from 1.5V to 5.5V
Capacitor Selection
Output Voltage Setting
R
V OUT
IN
1
OUT
=
may not be required. Alternatively, a
and calculate R
R
controls the amount of output volt-
2
=
V
V FB 1
FLY
OUT
IN
OUT
) controls the strength of the
IN
pin.
+
IN
. Increasing the size of
V
is very low, up to several
R 1 R 2
FB
may be substituted for
IN
1
2
–
from the following
and C
to be less than or
1
OUT
OUT
. These
and FB
2
). In
)
Note that the tolerance of the external resistors will
have an effect on the accuracy of the output voltage.
For optimum results, it is recommended that the
external resistors have a tolerance no larger than 1%.
5.3
The MCP1252 and MCP1253 family of devices transfer
charge at high switching frequencies, producing fast,
high peak, transient currents. As a result, any stray
inductance in the component layout will produce
unwanted noise in the system. Proper board layout
techniques are required to ensure optimum perfor-
mance. Figure 5-3 depicts the recommended board
layout. The input capacitor connected between V
GND, and the output capacitor connected between
V
1206 packages. The flying capacitor connected
between C+ and C- is a 1 µF ceramic, X7R dielectric in
a 0805 package. The layout is scaled 3:1.
FIGURE 5-3:
Circuit Board Layout.
V
GND
V
OUT
OUT
IN
and GND, are 10 µF ceramic, X7R dielectric, in
Recommended Layout
Recommended Printed
MCP1252/3
PGOOD
DS21752A-page 11
C+
C-
SELECT
SHDN
IN
and