MCP1624T-I View Datasheet(PDF) - Microchip Technology
Part Name
Description
MFG CO.
'MCP1624T-I' PDF : 30 Pages View PDF
MCP1623/24
4.2 Functional Description
The MCP1623/24 is a compact, high-efficiency,
fixed-frequency, step-up DC-DC converter that
provides an easy-to-use power supply solution for
PICĀ® microcontroller applications powered by either
single-cell, two-cell, or three-cell alkaline, NiCd, or
NiMH, and single-cell Li-Ion or Li-Polymer batteries.
Figure 4-1 depicts the functional block diagram of the
MCP1623/24.
4.2.1 LOW-VOLTAGE START-UP
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.
VOUT
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
capacitor, 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 āmotor-boatingā for deeply discharged batteries.
VIN
Internal
Bias
IZERO
Direction
Control
SW
Soft Start
0.3V
0V
Gate Drive
and
ILIMIT
EN
Shutdown
Control
Logic
ISENSE
GND
Oscillator
Slope
Comp.
S
PWM/PFM
Logic
FIGURE 4-1:
MCP1623/24 Block Diagram.
DS40001420D-page 12
1.21V
FB
EA
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