MIC2177-3.3BWM Micrel Inc, MIC2177-3.3BWM Datasheet - Page 8

no-image

MIC2177-3.3BWM

Manufacturer Part Number
MIC2177-3.3BWM
Description
IC REG SYNCBUCK 2.5A 3.3V 20SOIC
Manufacturer
Micrel Inc
Type
Step-Down (Buck)r
Datasheet

Specifications of MIC2177-3.3BWM

Internal Switch(s)
Yes
Synchronous Rectifier
Yes
Number Of Outputs
1
Voltage - Output
3.3V
Current - Output
2.5A
Frequency - Switching
200kHz
Voltage - Input
4.5 ~ 16.5 V
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
20-SOIC (7.5mm Width)
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Power - Output
-
Functional Description
Micrel’s MIC2177 is a synchronous buck regulator that
operates from an input voltage of 4.5V to 16.5V and
provides a regulated output voltage of 1.25V to 16.5V. It
has internal power MOSFETs that supply up to 2.5A of
load current and operates with up to 100% duty cycle to
allow low-dropout operation. To optimize efficiency, the
MIC2177 operates in PWM and skip mode. Skip mode
provides the best efficiency when load current is less
than 200mA, while PWM mode is more efficient at higher
current. A patented technique allows the MIC2177 to
automatically select the correct operating mode as the
load current changes.
During PWM operation, the MIC2177 uses current-mode
control which provides superior line regulation and
makes the control loop easier to compensate. The PWM
switching frequency is set internally to 200kHz and can
be synchronized to an external clock frequency up to
300kHz. Other features include a low-current shutdown
mode, current limit, undervoltage lockout, and thermal
shutdown. See the following sections for details.
Switch Output
The switch output (SW) is a half H-bridge consisting of a
high-side P-channel and low-side N-channel power
MOSFET. These MOSFETs have a typical on-resistance
of 100mΩ when the MIC2177 operates from a 12V
supply. Anti-shoot-through circuitry prevents the P-
channel and N-channel from turning on at the same
time.
Current Limit
The MIC2177 uses pulse-by-pulse current limiting to
protect the output. During each switching period, a
current limit comparator detects if the P-channel current
exceeds 4.7A. When it does, the P-channel is turned off
until the next switching period begins.
Undervoltage Lockout
Undervoltage lockout (UVLO) turns off the output when
the input voltage (V
drive for the output MOSFETs. It prevents the output
from turning on until V
the output will not shut off until V
Thermal Shutdown
Thermal shutdown turns off the output when the
MIC2177 junction temperature exceeds the maximum
value for safe operation. After thermal shutdown occurs,
the output will not turn on until the junction temperature
drops approximately 10°C.
Micrel, Inc.
April 2008
IN
) is too low to provide sufficient gate
IN
exceeds 4.3V. Once operating,
IN
drops below 4.2V.
8
Shutdown Mode
The MIC2177 has a low-current shutdown mode that is
controlled by the enable input (EN). When a logic 0 is
applied to EN, the MIC2177 is in shutdown mode and its
quiescent current drops to less than 5µA.
Internal Bias Regulator
An internal 3.3V regulator provides power to the
MIC2177 control circuits. This internal supply is brought
out to the BIAS pin for bypassing by an external 0.01µF
capacitor. Do not connect any external load to the BIAS
pin. It is not designed to provide an external supply
voltage.
Frequency Synchronization
The MIC2177 operates at a preset switching frequency
of 200kHz. It can be synchronized to a higher frequency
by connecting an external clock to the SYNC pin. The
SYNC pin is a logic level input that synchronizes the
oscillator to the rising edge of an external clock signal. It
has a frequency range of 220kHz–300kHz, and can
operate with a minimum pulse-width of 500ns. If
synchronization is not required, connect SYNC to
ground.
Low-Dropout Operation
Output regulation is maintained in PWM or skip mode
even when the difference between V
decreases below 1V. As V
cycle increases until it reaches 100%. At this point, the
P-channel is kept on for several cycles at a time, and the
output stays in regulation until V
dropout voltage (dropout voltage = P-channel on
resistance × load current).
PWM-Mode Operation
Refer to “PWM-Mode Functional Diagram” which is a
simplified block diagram of the MIC2177 operating in
PWM mode with its associated waveforms.
When operating in PWM mode, the output P-channel
and N-channel MOSFETs are alternately switched on at
a constant frequency and variable duty cycle. A
switching period begins when the oscillator generates a
reset pulse. This pulse resets the RS latch which turns
on the P-channel and turns off the N-channel. During
this time, inductor current (I
stored in the inductor. The current sense amplifier (I
Amp) measures the P-channel drain-to-source voltage
and outputs a voltage proportional to I
I
ramp) generated by the oscillator, creating a composite
waveform labeled I
I
comparator will set the RS latch which turns off the P-
channel and turns on the N-channel. Energy is then
SENSE
SENSE
Amp is added to a saw tooth waveform (corrective
is greater than the error amplifier output, the PWM
SENSE
on the timing diagram. When
IN
L1
– V
) increases and energy is
IN
OUT
– V
decreases, the duty
OUT
L1
. The output of
M9999-042108
falls below the
IN
MIC2177
and V
SENSE
OUT

Related parts for MIC2177-3.3BWM