MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
OPERATION
The MPQ4559 is a programmable frequency,
non-synchronous, step-down switching regulator
with an integrated high-side high voltage power
MOSFET. It provides a single highly efficient
solution with current mode control for fast loop
response and easy compensation. It features a
wide input voltage range, internal soft-start
control and precision current limiting. Its very low
operational quiescent current makes it suitable
for battery powered applications.
Internal Regulator
Most of the internal circuitries are powered from
the 2.6V internal regulator. This regulator takes
the VIN input and operates in the full VIN range.
When VIN is greater than 3.0V, the output of the
regulator is in full regulation. When VIN is lower
than 3.0V, the output decreases.
Enable Control
The MPQ4559 has a dedicated enable control
pin (EN). With high enough input voltage, the
chip can be enabled and disabled by EN which
has positive logic. Its falling threshold is a
precision 1.2V, and its rising threshold is 1.8V
(600mV higher).
PWM Control Mode
At moderate to high output current, the MPQ4559
operates in a fixed frequency, peak current
control mode to regulate the output voltage. A
PWM cycle is initiated by the internal clock. The
power MOSFET is turned on and remains on
until its current reaches the value set by the
COMP voltage. When the power switch is off, it
remains off for at least 100ns before the next
cycle starts. If, in one PWM period, the current in
the power MOSFET does not reach the COMP
set current value, the power MOSFET remains
on, saving a turn-off operation.
When floating, EN is pulled up to about 3.0V by
an internal 1µA current source so it is enabled.
To pull it down, 1µA current capability is needed.
When EN is pulled down below 1.2V, the chip is
put into the lowest shutdown current mode.
When EN is higher than zero but lower than its
rising threshold, the chip is still in shutdown
mode but the shutdown current increases
slightly.
Pulse Skipping Mode
Under-Voltage Lockout (UVLO)
Under light load condition the switching
frequency stretches down to zero to reduce the
switching loss and driving loss.
Under-voltage lockout (UVLO) is implemented to
protect the chip from operating at insufficient
supply voltage. The UVLO rising threshold is
about 3.0V while its falling threshold is a
consistent 2.6V.
Error Amplifier
The error amplifier compares the FB pin voltage
with the internal reference (REF) and outputs a
current proportional to the difference between the
two. This output current is then used to charge
the external compensation network to form the
COMP voltage, which is used to control the
power MOSFET current.
Internal Soft-Start
The soft-start is implemented to prevent the
converter output voltage from overshooting
during startup and short circuit recovery. When
the chip starts, the internal circuitry generates a
soft-start voltage (SS) ramping up from 0V to
2.6V. When it is lower than the internal reference
(REF), SS overrides REF so the error amplifier
uses SS as the reference. When SS is higher
than REF, REF regains control.
During operation, the minimum COMP voltage is
clamped to 0.9V and its maximum is clamped to
2.0V. COMP is internally pulled down to GND in
shutdown mode. COMP should not be pulled up
beyond 2.6V.
Thermal Shutdown
Thermal shutdown is implemented to prevent the
chip from operating at exceedingly high
temperatures. When the silicon die temperature
is higher than its upper threshold, it shuts down
the whole chip. When the temperature is lower
than its lower threshold, the chip is enabled
again.
MPQ4559 Rev. 1.01
5/24/2016
www.MonolithicPower.com
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