Microchip Technology ARD00558, User Manual

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MCP1632 Single Cell Li-Ion Battery Charger Demo Board User’s Guide
DS50002321A-page 10

2014 Microchip Technology Inc.
1.4 TECHNICAL SPECIFICATIONS
• Input voltage: +4.5V to +12V
• Load disconnect protection software configurable
• Typical output current: 1000 mA
• Maximum output current: 1500 mA (with firmware adjustments)
• Typical output power: 4.2W (maximum 7W at +25°C degree ambient temperature)
• Fully protected against Short-Circuit and No Load condition
• Figure 1-1 shows a simplified block diagram of the application
FIGURE 1-1: MCP1632 Block Diagram.
1.5 FUNCTIONAL DESCRIPTION
MCP1632 provides all the analog functions necessary to implement a stand-alone
switch-mode power converter. When combined with an external microcontroller, the
MCP1632 can be used to implement different intelligent converters like those
necessary for battery chargers.
The power train of this application uses the Single-Ended Primary Inductor Converter
(SEPIC) topology. This topology offers buck-boost functionality and also has
non-pulsating input current.
The converter provides constant voltage with limited current at the output, necessary
for certain battery charging applications (ex. Li-Ion-based batteries).
The output voltage is measured with a voltage divider resistor pair (R
1
, R
5
). This
voltage must be precisely 4.2V, required by the battery chemistry.
The average current in the L1B inductor, which is also the output current of the
converter, is sensed using a 0.1
Ω shunt resistor (R
S
). As the voltage across the shunt
resistor is negative, a -10x amplifier (U
3
) is used for battery charging current sensing.
The conversion gain of this circuit is 1V/A.
The PWM output available from the PIC12F1822 microcontroller is used to control the
reference voltage of the MCP1632 using the circuit created with D2 and R3 components.
Maximum output current is set by the PIC12F1822 microcontroller.
MCP1632
R
VREF
C
SS
V
IN
V
REF
COMP
EN
FB
CS
V
EXT
GND
V
IN
LDO
Q1
R
SENSE
R
SLOPE
L1A
D1
+
- C
IN
C
OUT
L1B
R
S
R
3
C
C
C
1
C
8
C
10
R
9
R
12
Battery
PIC12F1822
-
+
V
SENSE
C
SENSE
V
SENSE
Status
AN1
AN2
PWM
I/O
I/O
V
CC
D2
R
13
R
1
R
5
R
2
R
6
MCP6021