MCP1623-I/CH MICROCHIP [Microchip Technology], MCP1623-I/CH Datasheet - Page 11

• Manufacturer Part Number: MCP1623-I/CH
• Manufacturer: MICROCHIP [Microchip Technology]

4.2
The MCP1623/24 is a compact, high-efficiency, fixed
frequency, step-up DC-DC converter that provides an
easy-to-use
microcontroller applications powered by either one-cell,
two-cell, or three-cell alkaline, NiCd, or NiMH, or
one-cell Li-Ion or Li-Polymer batteries.
Figure 4-1 depicts the functional block diagram of the
MCP1623/24.
4.2.1
The MCP1623/24 is capable of starting from a low input
voltage. Start-up voltage is typically 0.65V for a 3.3V
output and 1 mA resistive load.
When enabled, the internal start-up logic turns the
rectifying P-Channel switch on until the output
capacitor is charged to a value close to the input
voltage. The rectifying switch is current limited during
this time. After charging the output capacitor to the
input voltage, the device starts switching. If the input
voltage is below 1.6V, the device runs open-loop with a
fixed duty cycle of 70% until the output reaches 1.6V.
FIGURE 4-1:
 2010 Microchip Technology Inc.
SW
EN
GND
V IN
Functional Description
LOW-VOLTAGE START-UP
power
MCP1623/24 Block Diagram.
supply
GATE DRIVE
SHUTDOWN
OSCILLATOR
solution
INTERNAL
CONTROL
PWM/PFM
LOGIC
LOGIC
AND
BIAS
for
PIC
V OUT
.3V
0V
DIRECTION
CONTROL
SLOPE
COMP.
SOFT-START
During this time, the boost switch current is limited to
50% of its nominal value. Once the output voltage
reaches 1.6V, normal closed-loop PWM operation is
initiated.
The MCP1623/24 charges an internal capacitor with a
very weak current source. The voltage on this capaci-
tor, in turn, slowly ramps the current limit of the boost
switch to its nominal value. The soft-start capacitor is
completely discharged in the event of a commanded
shutdown or a thermal shutdown.
There is no undervoltage lockout feature for the
MCP1623/24. The device will start-up at the lowest
possible voltage and run down to the lowest possible
voltage. For typical battery applications, this may result
in “motor-boating” for deeply discharged batteries.
EA
I
I LIMIT
I SENSE
ZERO

1.21V
MCP1623/24
DS41420A-page 11
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