Analog and Interface Solutions
Portable Power Conversion Design Guide
www.microchip.com/analog
Design Guide
Introduction and Contents
Portable power conversion applications present unique and challenging design considerations. Innovative, small electronics
require solutions with small footprints. In order to maintain battery life, portable applications require both high conversion
efficiency and low standby power dissipation. Multi-cell battery packs may require step-down (buck) conversions and single
cell batteries often require step-up (boost) conversions to maintain consistent power levels while the batteries discharge.
Some products require constant voltage regulation for microcontrollers, sensors or RF signal processing; while some
circuits need constant current regulation for backlighting or battery charging. Microchip offers a broad array of solutions
which feature small package sizes, high-efficiency, low standby power, accuracy and versatility solutions to solve these
portable power conversion challenges.
Table of Contents
Step-Down (Buck) Switch Mode Power Converters . . . . . . . . . . . . . . . . . . . . . . . 2
Linear (Low Drop Out) Regulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Step-Up (Boost) Switch Mode Power Converters . . . . . . . . . . . . . . . . . . . . . . . 12
Backlighting Solutions with Switching Regulators . . . . . . . . . . . . . . . . . . . . . . 17
Backlighting Solutions with Charge Pump DC/DC Converters . . . . . . . . . . . . . . 19
Linear Battery Chargers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Programmable Battery Chargers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Application Notes and Demonstration Boards . . . . . . . . . . . . . . . . . . . . . . . . . 24
DC/DC Conversion
Step-Down (Buck) Switch Mode Power Converters
Step-Down (Buck) Switch Mode Power Converters
For wide input range voltage sources and high output current applications switch-mode power converters offer a significant
increase in efficiency compared to linear regulators. This results in longer battery run time in portable applications.
Step-down or buck converters are used to regulate an output voltage that is always lower than the source voltage. Using
inductors and capacitors for energy storage allows buck converters to commonly be more than 90% efficient, and under
some circumstances they can be more than 95% efficient.
Microchip offers a wide selection of buck converters and PWM controllers. Many of them are specifically designed to convert
power from NiMH, Ni-Cd, Li-Ion, Alkaline multi-cell or 12/24V SLA batteries. Converters integrate power MOSFET switches
used to commutate the supply current, while controllers rely on external power MOSFETs in diodes to switch the converter
current. Synchronous converters rely on two MOSFETs working together to control the current flow, while asynchronous
converters replace one MOSFET with a freewheeling power diode. Synchronous converters deliver higher efficiency for low
output voltages, especially less than 3.3V, while asynchronous converters work well for higher output voltages.
2
Portable Power Conversion Design Guide
DC/DC Conversion
Step-Down (Buck) Switch Mode Power Converters
MCP16301/H 36V Input Voltage Non-Synchronous Buck Converter
The MCP16301 is a highly integrated, high-efficiency, fixed-frequency, step-down DC-DC converter in a popular 6-pin SOT-23
package. This converter operates from voltage sources up to 30V, including the integrated high-side switch, fixed-frequency Peak
Current Mode Control, internal compensation, peak current limit and over-temperature protection. This device allows you to build
DC/DC conversion circuits with minimal external components.
■
12V and 24V industrial/SLA
battery input DC-DC conversion
■
Up to 96% typical efficiency
■
Wide input voltage range:
• 4.0V to 30V (MCP16301)
• 4.7V to 36V (MCP16301H)
■
Output voltage range: 2.0V to 15V
■
2% output voltage accuracy
■
Integrated 460 mΩ n-channel
buck switch
■
600 mA output current
■
500 kHz fixed frequency
■
Adjustable output voltage
■
Low device shutdown current
■
Peak current mode control
■
Internal compensation
■
Stable with ceramic capacitors
■
■
■
■
Internal soft-start
Cycle-by-cycle peak current limit
Under voltage lockout (UVLO) at 3.5V
Extended −40 to +125°C operating
temperature range
■
Over-temperature protection
■
D2PAK package linear regulator
replacement
■
Available in 6-pin SOT-23 package
Example MCP16301 Non-Synchronous Buck Regulator Application Circuit
1N4148
C
BOOST
100 nF
V
IN
4.5V to 30V
C
IN
10 µF
BOOST
V
IN
EN
GND
SW
L
1
15 H
V
OUT
3.3V @ 600 mA
C
OUT
2 × 10 F
40V
Schottky
Diode
31.2 kΩ
V
FB
10 kΩ
Typical MCP16301 Power Conversion Efficiency
with a Fixed 5.0V Output
100
90
V
IN
= 6V
MCP16301 Light Load Operation
Efficiency (%)
80
70
V
IN
= 12V
V
IN
= 30V
V
OUT
= 5.0V
60
50
40
30
I
L
0
100
200
300
I
OUT
(mA)
400
500
600
Portable Power Conversion Design Guide
3
DC/DC Conversion
Step-Down (Buck) Switch Mode Power Converters
MCP16311/2 30V Input, High-Efficiency, Integrated Synchronous Buck Regulator
The MCP16311 is a compact, high-efficiency, fixed-frequency PWM/PFM, synchronous step-down DC-DC converter in a
8-pin MSOP or 2 × 3 TDFN package that operates from input voltage sources up to 30V. Integrated features include a high-
side and a low-side switch, fixed-frequency Peak Current Mode Control, internal compensation, peak-current limit and over-
temperature protection. The MCP16311 provides all the active functions for local DC-DC conversion, with fast transient
response and accurate regulation.
■
Up to 95% efficiency
■
Wide 4.4V to 30V input
voltage range
■
Wide 2.0V to 24V output
voltage range
■
Integrated high-performance
n-channel low- and high-side
switches: 170 mΩ low-side MOSFET,
300 mΩ high-side MOSFET
■
Stable 0.8V reference voltage
■
Automatic pulse-frequency
modulation/pulse-width modulation
(PFM/PWM) operation (on
MCP16311), or 500 kHz PWM only
operation (on MCP16312)
■
Low 3 μA (typical) device
shutdown current
■
Low 44 μA device quiescent current
(when not switching in PFM Mode)
■
Internal compensation
■
■
■
■
Internal soft-start: 300 μs turn on
Peak current mode control
Cycle-by-cycle peak current limit
Under-voltage lockout
(UVLO) at 3.6V (typical) with
0.5V of hysteresis
■
Thermal shutdown at 150°C, with
25°C hysteresis
Example MCP16311 Synchronous Buck Regulator Application Circuit
V
IN
4.5V to 30V
C
IN
2 ×10 µF
C
BOOST
100 nF
BOOST
V
IN
EN
V
CC
SW
L
1
15 H
V
OUT
3.3V @ 1A
C
OUT
2 × 10 F
31.2 kΩ
V
FB
10 kΩ
Cv
CC
1 µF
GND
MCP16311 Ouput Current Capability
1600
1400
1200
I
OUT
(mA)
1000
800
600
400
200
0
0
5
10
15
V
IN
(V)
20
25
30
V
OUT
= 3.3V
V
OUT
= 5V
Typical MCP16311 Efficiency, with and without
V
PFM Operation Enabled
100
90
V
OUT
= 5V
V
OUT
= 3.3V
80
Efficiency (%)
V
OUT
= 12V
70
60
50
40
30
20
10
V
IN
= 12V
PWM ONLY
PWM/PFM
0
1
10
I
OUT
(mA)
100
1000
4
Portable Power Conversion Design Guide
DC/DC Conversion
Step-Down (Buck) Switch Mode Power Converters
MCP16311 12V Buck-Boost Application
Some power supplies require the ability step the voltage up or down from the input to the output. This is particularly useful
in battery-powered applications where the battery voltage may be above or below the desired output voltage, depending on
the type of battery used or battery charge remaining. By adding a few additional circuit components, the MCP16311 can be
adapted to work in a buck-boost topology that would address this issue. The application can either buck or boost the input
voltage in order to maintain the output voltage, operating from a 6V to 18V input and providing up to 300 mA of output current.
MCP16311 Buck-Boost Application Circuit
R
EN
1 MΩ
EN
V
IN
= 4.5V to 18V
C
1
10 µF
C
2
10 µF
BOOST
L
1
SW
V
IN
V
CC
C
VCC
1 µF
D
1
D
S
40V Schottky Diode
Q
1
30V n-Channel
MOSFET
C
3
10 µF
C
4
10 µF
56 H
R
6
G
RB
140 kΩ
RT
10 kΩ
V
OUT
GND
FB
P
GND
4.7Ω
A
GND
GND
1
Portable Power Conversion Design Guide
5
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