MPQ4560 – 2A, 2MHz, 55V, STEP-DOWN CONVERTER
Enable Control
The MPQ4560 has a dedicated enable control
pin (EN) that can enable or disable the chip when
the input voltage exceeds an upper threshold. Its
falling threshold (turn-off) is 1.2V, and its rising
threshold (turn-on) is 1.5V (300mV higher).
OPERATION
The MPQ4560 is an asynchronous, step-down,
switching regulator with an integrated high-side,
high-voltage,
power
MOSFET
and
a
programmable frequency. 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 precise current limiting. Its very
low operational quiescent current makes it
suitable for battery-powered applications.
When floating, an internal 1µA current source
pulls EN up to ~3.0V to enable the chip. Pull-
down requires a 1µA current.
When EN is pulled below 1.2V, the chip enters its
lowest shutdown current mode. When EN
exceeds 0V but remains lower than its rising
threshold, the chip remains in shutdown mode
but the shutdown current increases slightly.
PWM Control
The MPQ4560 operates in a fixed-frequency,
peak-current-control mode to regulate the output
voltage at moderate-to-high output current. The
internal clock initiates a PWM cycle. The power
MOSFET turns 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 the current in the power MOSFET
does not reach the COMP-set current value
within one PWM period, the power MOSFET
remains ON, saving a turn-off operation.
Under-Voltage Lockout
Under-voltage lockout (UVLO) protects 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.
Internal Soft-Start
Soft-start prevents the converter output voltage
from overshooting during startup and short-circuit
recovery. When the chip starts, the internal circuit
generates a soft-start voltage (SS) ramping up
Pulse-Skipping Mode
from 0V to 2.6V. When it is less than the VREF
,
Under light-load condition the switching
frequency stretches the zero-voltage period to
reduce the switching loss and driving loss.
SS overrides VREF so the error amplifier uses SS
as the reference. When SS exceeds VREF, VREF
regains control.
Error Amplifier
Thermal Shutdown
The error amplifier compares the FB pin voltage
(VFB) to the internal reference (VREF) and outputs
a current proportional to the difference. This
Thermal shutdown prevents the chip from
operating at exceedingly high temperatures.
When the silicon die temperature exceeds its
upper threshold, the whole chip shuts down.
When the temperature is less than its lower
threshold, the chip is enabled again.
output
current
charges
the
external
compensation network to form VCOMP, which
controls the power MOSFET current.
During operation, the minimum VCOMP is clamped
to 0.9V and its maximum is clamped to 2.0V.
COMP is internally pulled down to GND in
shutdown mode. Do not pull VCOMP above 2.6V.
Floating Driver and Bootstrap Charging
An external bootstrap capacitor powers the
floating power MOSFET driver. This floating
driver has its own UVLO protection. This UVLO’s
rising threshold is 2.2V with a hysteresis of
150mV. The driver’s UVLO is soft-start related:
When the bootstrap voltage hits its UVLO
threshold, the soft-start circuit resets. To prevent
noise, there is 20µs delay before the reset action.
When bootstrap UVLO is gone, the reset is off
and then the soft-start process resumes.
Internal Regulator
An internal 2.6V regulator powers most of the
internal circuits. This regulator takes the VIN
input and operates in the full VIN range. When VIN
exceeds 3.0V, the output of the regulator is in full
regulation. When VIN is less than 3.0V, the output
decreases.
The dedicated internal bootstrap regulator
regulates and charges the bootstrap capacitor to
MPQ4560 Rev. 1.1
3/29/2013
www.MonolithicPower.com
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