MCP1623-I/CH MICROCHIP [Microchip Technology], MCP1623-I/CH Datasheet - Page 12

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

MCP1623/24
4.2.2
In normal PWM operation, the MCP1623/24 operates
as a fixed frequency, synchronous boost converter. The
switching frequency is internally maintained with a
oscillator typically set to 500 kHz. The MCP1623
device will operate in PWM-only mode even during
periods of light load operation. By operating in
PWM-only mode, the output ripple remains low and the
frequency is constant. Operating in fixed PWM mode
results in lower efficiency during light load operation
(when compared to PFM mode (MCP1624).
Lossless current sensing converts the peak current sig-
nal to a voltage to sum with the internal slope compen-
sation. This summed signal is compared to the voltage
error amplifier output to provide a peak current control
command
compensation is adaptive to the input and output
voltage. Therefore, the converter provides the proper
amount of slope compensation to ensure stability, but is
not excessive, which causes a loss of phase margin.
The peak current limit is set to 425 mA typical.
4.2.3
The MCP1624 device is capable of operating in normal
PWM mode and PFM mode to maintain high efficiency
at all loads. In PFM mode, the output ripple has a vari-
able frequency component that changes with the input
voltage and output current. With no load, the quiescent
current draw from the output is typically 19 µA. The
PFM mode can be disabled in selected device options.
PFM operation is initiated if the output load current falls
below an internally programmed threshold. The output
voltage is continuously monitored. When the output
voltage drops below its nominal value, PFM operation
pulses one or several times to bring the output back
into regulation. If the output load current rises above
the upper threshold, the MCP1624 transitions smoothly
into PWM mode.
4.2.4
The MCP1623/24 output voltage is adjustable with a
resistor divider over a 2.0V minimum to 5.5V maximum
range. High value resistors are recommended to mini-
mize quiescent current to keep efficiency high at light
loads.
4.2.5
The enable pin is used to turn the boost converter on
and off. The enable threshold voltage varies with input
voltage. To enable the boost converter, the EN voltage
level must be greater than 90% of the V
disable the boost converter, the EN voltage must be
less than 20% of the V
DS41420A-page 12
PWM MODE OPERATION
PFM MODE OPERATION
ADJUSTABLE OUTPUT VOLTAGE
ENABLE/OUTPUT DISCONNECT
for
the
IN
PWM
voltage.
signal.
IN
The
voltage. To
slope
The MCP1623/24 devices incorporate a true output
disconnect feature. With the EN pin pulled low, the
output of the MCP1623/24 is isolated or disconnected
from the input by turning off the integrated P-Channel
switch and removing the switch bulk diode connection.
This removes the DC path typical in boost converters,
which allows the output to be disconnected from the
input. During this mode, less than 1 µA of current is
consumed from the input (battery). True output discon-
nect does not discharge the output; the output voltage
is held up by the external C
4.2.6
The MCP1623/24 gets its start-up bias from V
the output exceeds the input, bias comes from the
output.
completely independent of V
limited by the output power level and the input source
series resistance. Once started, the output will remain
in regulation down to 0.35V typical with 1 mA output
current for low source impedance inputs.
4.2.7
The error amplifier, with its associated compensation
network, completes the closed loop system by com-
paring the output voltage to a reference at the input of
the error amplifier, and feeding the amplified and
inverted signal to the control input of the inner current
loop. The compensation network provides phase leads
and lags at appropriate frequencies to cancel exces-
sive phase lags and leads of the power circuit. All nec-
essary
compensation are integrated.
4.2.8
Unlike most boost converters, the MCP1623/24 allows
its output to be shorted during normal operation. The
internal current limit and overtemperature protection limit
excessive stress and protect the device during periods
of short circuit, overcurrent and overtemperature.
4.2.9
The MCP1623/24 integrates a low noise anti-ring
switch that damps the oscillations typically observed at
the switch node of a boost converter when operating in
the Discontinuous Inductor Current mode. This
removes the high frequency radiated noise.
4.2.10
Overtemperature protection circuitry is integrated in the
MCP1623/24. This circuitry monitors the device junction
temperature and shuts the device off if the junction
temperature exceeds the typical +150
this threshold is exceeded, the device will automatically
restart once the junction temperature drops by 10
The soft start is reset during an overtemperature
condition.
Therefore,
compensation
INTERNAL BIAS
INTERNAL COMPENSATION
SHORT CIRCUIT PROTECTION
LOW NOISE OPERATION
OVERTEMPERATURE
PROTECTION
once
 2010 Microchip Technology Inc.
components
OUT
started,
IN
capacitance.
. Operation is only
o
C threshold. If
operation
and
IN
. Once
slope
o
C.
is