MCP1623-I/CH MICROCHIP [Microchip Technology], MCP1623-I/CH Datasheet - Page 10

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

MCP1623/24
4.0
4.1
The MCP1623/24 family of devices is capable of low
start-up voltage and delivers high efficiency over a wide
load range for single cell, two cell, three cell alkaline,
NiMH, NiCd and single cell Li-Ion battery inputs. A high
level of integration lowers total system cost, eases
implementation and reduces board area. The devices
feature low start-up voltage, adjustable output voltage,
PWM/PFM mode operation, low I
nous switch, internal compensation, low noise anti-ring
control, inrush current limit and soft start. There is one
feature option for the MCP1623/24 family: PWM/PFM
mode or PWM mode only.
4.1.1
The MCP1624 devices use an automatic switchover
from PWM to PFM mode for light load conditions to
maximize efficiency over a wide range of output current.
During PFM mode, higher peak current is used to pump
the output up to the threshold limit. While operating in
PFM or PWM mode, the P-Channel switch is used as a
synchronous rectifier, turning off when the inductor
current reaches 0 mA to maximize efficiency. In PFM
mode, a comparator is used to terminate switching when
the output voltage reaches the upper threshold limit.
Once switching has terminated, the output voltage will
decay or coast down. During this period, very low I
consumed from the device and input source, which
keeps power efficiency high at light load. The
disadvantages of PWM/PFM mode are higher output
ripple voltage and variable PFM mode frequency. The
PFM mode frequency is a function of input voltage,
output voltage and load. While in PFM mode, the boost
converter pumps the output up at a switching frequency
of 500 kHz.
DS41420A-page 10
DETAILED DESCRIPTION
Device Option Overview
PWM/PFM MODE OPTION
Q
, integrated synchro-
Q
is
4.1.2
The MCP1623 devices disable PFM mode switching,
and operate only in PWM mode over the entire load
range. During periods of light load operation, the
MCP1623 continues to operate at a constant 500 kHz
switching frequency, keeping the output ripple voltage
lower than PFM mode. During PWM-only mode, the
MCP1623 P-Channel switch acts as a synchronous
rectifier by turning off to prevent reverse current flow
from the output cap back to the input in order to keep
efficiency high. For noise immunity, the N-Channel
MOSFET current sense is blanked for approximately
100 ns. With a typical minimum duty cycle of 100 ns,
the MCP1623 continues to switch at a constant
frequency under light load conditions.
represents the input voltage versus load current for the
pulse-skipping threshold in PWM-only mode. At lighter
loads, the MCP1623 device begins to skip pulses.
TABLE 4-1:
MCP1624
MCP1623
Part Number
PWM MODE ONLY OPTION
PART NUMBER SELECTION
 2010 Microchip Technology Inc.
PWM/PFM
X
Figure 2-12
PWM
X