MPQ4559-AEC1
Industrial Grade, 1.5A, 2MHz, 55V
Step-Down Converter
AEC-Q100 Qualified
DESCRIPTION
FEATURES
The MPQ4559 is a high frequency step-down
switching regulator with integrated internal highside high voltage power MOSFET. It provides
1.5A output with current mode control for fast loop
response and easy compensation.
The wide 3.8V to 55V input range accommodates
a variety of step-down applications, including
those in automotive input environment. A 12µA
shutdown mode supply current allows use in
battery-powered applications.
High power conversion efficiency over a wide
load range is achieved by scaling down the
switching frequency at light load condition to
reduce the switching and gate driving losses.
The frequency foldback helps prevent inductor
current runaway during startup and thermal
shutdown provides reliable, fault tolerant
operation.
By switching at 2MHz, the MPQ4559 is able to
prevent EMI (Electromagnetic Interference) noise
problems, such as those found in AM radio and
ADSL applications.
Guaranteed Industrial Temp Range Limits
Wide 3.8V to 55V Operating Input Range
250mΩ Internal Power MOSFET
Up to 2MHz Programmable Switching
Frequency
140μA Quiescent Current
Ceramic Capacitor Stable
Internal Soft-Start
Up to 95% Efficiency
Output Adjustable from 0.8V to 52V
Available in QFN (3mm x 3mm) and
SOIC8E with Exposed Pad Packages
AEC-Q100 Qualified
APPLICATIONS
High Voltage Power Conversion
Automotive Systems
Industrial Power Systems
Distributed Power Systems
Battery Powered Systems
All MPS parts are lead-free and adhere to the RoHS directive. For MPS green
status, please visit MPS website under Quality Assurance. “MPS” and “The
Future of Analog IC Technology” are Registered Trademarks of Monolithic
Power Systems, Inc.
The MPQ4559 is available in small 3mm x 3mm
QFN10 and SOIC8 with exposed pad packages..
TYPICAL APPLICATION
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
ORDERING INFORMATION
Part Number
Package
Top Marking
MPQ4559DN*
SOIC8E
MP4559DN
MPQ4559DQ**
QFN10 (3X3mm)
ADD
MPQ4559DQ-AEC1
QFN10 (3X3mm)
ADD
* For Tape & Reel, add suffix –Z (e.g. MPQ4559DN–Z)
For RoHS Compliant Packaging, add suffix –LF (e.g. MPQ4559DN–LF–Z)
* For Tape & Reel, add suffix –Z (e.g. MPQ4559DQ–Z)
For RoHS Compliant Packaging, add suffix –LF (e.g. MPQ4559DQ–LF–Z)
PACKAGE REFERENCE
QFN10
SOIC8 (Exposed Pad)
ABSOLUTE MAXIMUM RATINGS (1)
Thermal Resistance
Supply Voltage (VIN).................... –0.3V to +60V
Switch Voltage (VSW)............ –0.5V to VIN + 0.5V
BST to SW .................................... –0.3V to +5V
All Other Pins ................................ –0.3V to +5V
Continuous Power Dissipation
(TA = +25°C) (2)
SOIC8E……………………………………….2.5W
QFN10 (3X3mm)…………………………….2.5W
Junction Temperature .............................. 150C
Lead Temperature ................................... 260C
Storage Temperature .............. –65°C to +150C
SOIC8 (Exposed Pad) ............ 50 ...... 10 ... C/W
QFN10 (3X3mm)………………50……12…C/W
Recommended Operating Conditions
(3)
Supply Voltage VIN .......................... 3.8V to 55V
Output Voltage VOUT........................ 0.8V to 52V
Operating Junct. Temp (TJ) ..... –40C to +125C
(4)
θJA
θJC
Notes:
1) Exceeding these ratings may damage the device
2) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ(MAX), the junction-toambient thermal resistance θJA, and the ambient temperature
TA. The maximum allowable continuous power dissipation at
any ambient temperature is calculated by PD(MAX)=(TJ(MAX)TA)/ θJA. Exceeding the maximum allowable power dissipation
will cause excessive die temperature, and the regulator will go
into thermal shutdown. Internal thermal shutdown circuitry
protects the device from permanent damage.
3) The device is not guaranteed to function outside of its
operating conditions.
4) Measured on JESD51-7 4-layer board.
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
ELECTRICAL CHARACTERISTICS
VIN = 12V, VEN = 2.5V, VCOMP = 1.4V, TJ= –40C to +125C. Typical Values are at TJ=25C, unless
otherwise noted.
Parameter
Symbol Condition
Feedback Voltage
VFB
TJ =25C
4.5V < VIN < 55V -40°C ≤ TJ ≤85°C
-40°C ≤ TJ ≤125°C
Feedback Leakage Current
Upper Switch On Resistance
IFB
(5)
RDS(ON)
Upper Switch Leakage
ISW
Current Limit
ILIM
COMP to Current Sense
Transconductance
Error Amp Voltage Gain
Error Amp Transconductance
Error Amp Min Source current
Error Amp Min Sink current
Duty Cycle ≤ 60%
175
160
1.9
1.8
2.7
2.4
0V < VFB < 0.8V
fSW
Shutdown Supply Current
IS
Quiescent Supply Current
IQ
EN Rising Threshold
VEN = 0V, VSW = 0V
TJ=25C
ICOMP = ±3µA
VFB = 0.7V
VFB = 0.9V
TJ=25C
VIN UVLO Hysteresis
(5)
Soft-Start Time
Thermal Shutdown
Minimum Off Time
(5)
Minimum On Time
VBST – VSW = 5V
TJ=25C
GCS
VIN UVLO Threshold
Oscillator Frequency
Min
0.780
0.772
0.766
RFREQ = 95kΩ
TJ =25C
0.19
0.8
0.7
VEN < 0.3V
No load, VFB = 0.9V (no
switching)
Hysteresis = 20C
TOFF
TON
TJ=25C
EN Threshold Hysteresis
1.4
1.3
Typ
0.800
0.1
250
1
2.3
Max
0.820
0.829
0.829
1.0
330
400
Units
V
μA
mΩ
μA
4.5
4.7
A
5.7
A/V
400
120
10
-10
3.0
3.0
0.35
0.5
1
V/V
µA/V
µA
µA
V
3.3
3.6
12
1.2
1.3
20
140
200
150
100
100
1.55
320
1.7
1.8
V
ms
MHz
µA
µA
C
ns
ns
V
mV
Note:
5) Derived from bench characterization. Not tested in production.
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
PIN FUNCTIONS
QFN
Pin #
SOIC8
Pin #
1, 2
1
3
2
4
3
5
4
6
5
7
6
8, 9
7
10
8
Name
Description
Switch Node. Output from the high-side switch. A low VF Schottky rectifier to ground
is required. The rectifier must be close to the SW pins to reduce switching spikes.
Enable Input. Pull this pin below the specified threshold to shutdown the chip. Pull it
EN
up above the specified threshold or leaving it floating to enable the chip.
Compensation. Output of the GM error amplifier. Control loop frequency
COMP
compensation is applied to this pin.
Feedback. Input to the error amplifier. Sets the regulator voltage by comparing the
FB
tap of an external resistive divider connected between the output and GND to the
internal +0.8V reference.
GND, Ground. Connect as close as possible to the output capacitor and avoid the highExposed current switch paths. Connect exposed pad to GND plane for optimal thermal
pad
performance.
Switching Frequency Program Input. Connect a resistor from this pin to ground to set
FREQ
the switching frequency.
Input Supply. This supplies power to all the internal control circuitry, both BS
VIN
regulators, and the high-side switch. Place a decoupling capacitor to ground close to
this pin to minimize switching spikes.
SW
BST
Bootstrap. Positive power supply for the internal floating high-side MOSFET driver.
Connect a bypass capacitor between this pin and SW pin.
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT =3.3V, C1 = 4.7µF, C2 = 22µF, L1 = 10µH and TA = +25C, unless otherwise noted.
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT =3.3V, C1 = 4.7µF, C2 = 22µF, L1 = 10µH and TA = +25C, unless otherwise noted.
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
BLOCK DIAGRAM
Figure 1—Functional Block Diagram
MPQ4559 Rev. 1.01
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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.
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.
Pulse Skipping Mode
Under light load condition the switching
frequency stretches down to zero to reduce the
switching loss and driving loss.
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.
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.
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).
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.
Under-Voltage Lockout (UVLO)
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.
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.
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
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
Floating Driver and Bootstrap Charging
The floating power MOSFET driver is powered by
an external bootstrap capacitor. 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. In
case the bootstrap voltage hits its UVLO, the
soft-start circuit is reset. To prevent noise, there
is 20µs delay before the reset action. When
bootstrap UVLO is gone, the reset is off and then
soft-start process resumes.
The bootstrap capacitor is charged and regulated
to about 5V by the dedicated internal bootstrap
regulator. When the voltage between the BST
and SW nodes is lower than its regulation, a
PMOS pass transistor connected from VIN to
BST is turned on. The charging current path is
from VIN, BST and then to SW. External circuit
should provide enough voltage headroom to
facilitate the charging.
As long as VIN is sufficiently higher than SW, the
bootstrap capacitor can be charged. When the
power MOSFET is ON, VIN is about equal to SW
so the bootstrap capacitor cannot be charged.
When the external diode is on, the difference
between VIN and SW is largest, thus making it
the best period to charge. When there is no
current in the inductor, SW equals the output
voltage VOUT so the difference between VIN and
VOUT can be used to charge the bootstrap
capacitor.
At higher duty cycle operation condition, the time
period available to the bootstrap charging is less
so the bootstrap capacitor may not be sufficiently
charged.
In case the internal circuit does not have
sufficient voltage and the bootstrap capacitor is
not charged, extra external circuitry can be used
to ensure the bootstrap voltage is in the normal
operational region. Refer to External Bootstrap
Diode in Application section.
The DC quiescent current of the floating driver is
about 20µA. Make sure the bleeding current at
the SW node is higher than this value, such that:
IO
Current Comparator and Current Limit
The power MOSFET current is accurately sensed
via a current sense MOSFET. It is then fed to the
high speed current comparator for the current
mode control purpose. The current comparator
takes this sensed current as one of its inputs.
When the power MOSFET is turned on, the
comparator is first blanked till the end of the turnon transition to avoid noise issues. The
comparator then compares the power switch
current with the COMP voltage. When the
sensed current is higher than the COMP voltage,
the comparator output is low, turning off the
power MOSFET. The cycle-by-cycle maximum
current of the internal power MOSFET is
internally limited.
Short Circuit Protection
When the output is shorted to the ground, the
switching frequency is folded back and the
current limit is reduced to lower the short circuit
current. When the voltage of FB is at zero, the
current limit is reduced to about 50% of its full
current limit. When FB voltage is higher than
0.4V, current limit reaches 100%.
In short circuit FB voltage is low, the SS is pulled
down by FB and SS is about 100mV above FB.
In case the short circuit is removed, the output
voltage will recover at the SS pace. When FB is
high enough, the frequency and current limit
return to normal values.
Startup and Shutdown
If both VIN and EN are higher than their
appropriate thresholds, the chip starts. The
reference block starts first, generating stable
reference voltage and currents, and then the
internal regulator is enabled. The regulator
provides stable supply for the remaining
circuitries.
While the internal supply rail is up, an internal
timer holds the power MOSFET OFF for about
50µs to blank the startup glitches. When the
internal soft-start block is enabled, it first holds its
SS output low to ensure the remaining circuitries
are ready and then slowly ramps up.
VO
20A
(R1 R2)
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
Three events can shut down the chip: EN low,
VIN low and thermal shutdown. In the shutdown
procedure, power MOSFET is turned off first to
avoid any fault triggering. The COMP voltage and
the internal supply rail are then pulled down.
Programmable Oscillator
The MPQ4559 oscillating frequency is set by an
external resistor, RFREQ from the FREQ pin to
ground. The value of RFREQ can be calculated
from:
RFREQ (kΩ) =
100000
-5
fS (kHz)
To get fSW=500kHz, RFREQ=195kΩ.
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
APPLICATION INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
The output voltage is set using a resistive voltage
divider from the output voltage to FB pin. The
voltage divider divides the output voltage down to
the feedback voltage by the ratio:
VFB =VOUT
R2
R1+R2
Thus the output voltage is:
VOUT =VFB
A good rule for determining the inductance to use
is to allow the peak-to-peak ripple current in the
inductor to be approximately 30% of the
maximum switch current limit. Also, make sure
that the peak inductor current is below the
maximum switch current limit. The inductance
value can be calculated by:
R1+R2
R2
For example, the value for R2 can be 10kΩ. With
this value, R1 can be determined by:
R1=12.5 (VOUT -0.8)(KΩ)
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 31.6kΩ.
Inductor
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value
inductor will result in less ripple current that will
result in lower output ripple voltage. However, the
larger value inductor will have a larger physical
size, higher series resistance, and/or lower
saturation current.
L1=
VOUT
fs ΔIL
(1-
VOUT
VIN
)
Where VOUT is the output voltage, VIN is the input
voltage, fS is the switching frequency, and ∆IL is
the peak-to-peak inductor ripple current.
Choose an inductor that will not saturate under
the maximum inductor peak current. The peak
inductor current can be calculated by:
ILP ILOAD
VOUT
V
1 OUT
2 fS L1
VIN
Where ILOAD is the load current.
Table 1 lists a number of suitable inductors from
various manufacturers. The choice of which style
inductor to use mainly depends on the price vs.
size requirements and any EMI requirement.
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
Table 1—Inductor Selection Guide
Inductance
Max DCR
Current Rating
Dimensions
(µH)
(Ω)
(A)
L x W x H (mm3)
7447789004
4.7
0.033
2.9
7.3x7.3x3.2
744066100
10
0.035
3.6
10x10x3.8
744771115
15
0.025
3.75
12x12x6
744771122
22
0.031
3.37
12x12x6
RLF7030T-4R7
4.7
0.031
3.4
7.3x6.8x3.2
SLF10145T-100
10
0.0364
3
10.1x10.1x4.5
SLF12565T-150M4R2
15
0.0237
4.2
12.5x12.5x6.5
SLF12565T-220M3R5
22
0.0316
3.5
12.5x12.5x6.5
FDV0630-4R7M
4.7
0.049
3.3
7.7x7x3
919AS-100M
10
0.0265
4.3
10.3x10.3x4.5
919AS-160M
16
0.0492
3.3
10.3x10.3x4.5
919AS-220M
22
0.0776
3
10.3x10.3x4.5
Part Number
Wurth Electronics
TDK
Toko
Output Rectifier Diode
The output rectifier diode supplies the current to
the inductor when the high-side switch is off. To
reduce losses due to the diode forward voltage
and recovery times, use a Schottky diode.
Choose a diode whose maximum reverse voltage
rating is greater than the maximum input voltage,
and whose current rating is greater than the
maximum load current. Table 2 lists example
Schottky diodes and manufacturers.
Table 2—Diode Selection Guide
Diodes
B290-13-F
B380-13-F
CMSH2-100M
CMSH3-100MA
Voltage/
Current Rating
90V, 2A
80V, 3A
100V, 2A
100V, 3A
Manufacturer
Diodes Inc.
Diodes Inc.
Central Semi
Central Semi
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required to
supply the AC current to the step-down converter
while maintaining the DC input voltage. Use low
ESR capacitors for the best performance.
Ceramic capacitors are preferred, but tantalum or
low-ESR electrolytic capacitors may also suffice.
For simplification, choose the input capacitor with
RMS current rating greater than half of the
maximum load current. The input capacitor (C1)
can be electrolytic, tantalum or ceramic.
When using electrolytic or tantalum capacitors, a
small, high quality ceramic capacitor, i.e. 0.1μF,
should be placed as close to the IC as possible.
When using ceramic capacitors, make sure that
they have enough capacitance to provide
sufficient charge to prevent excessive voltage
ripple at input. The input voltage ripple caused by
capacitance can be estimated by:
I
V
V
VIN LOAD OUT 1 OUT
fS C1 VIN
VIN
Output Capacitor
The output capacitor (C2) is required to maintain
the DC output voltage. Ceramic, tantalum, or low
ESR electrolytic capacitors are recommended.
Low ESR capacitors are preferred to keep the
output voltage ripple low. The output voltage
ripple can be estimated by:
VOUT
VOUT
V
1 OUT
f S L
VIN
1
R ESR
8
f
C
2
S
Where L is the inductor value and RESR is the
equivalent series resistance (ESR) value of the
output capacitor.
In the case of ceramic capacitors, the impedance
at the switching frequency is dominated by the
capacitance. The output voltage ripple is mainly
caused by the capacitance. For simplification, the
output voltage ripple can be estimated by:
ΔVOUT
V
1 OUT
2
VIN
8 fS L C2
VOUT
ΔVOUT
VOUT
V
1 OUT
fS L
VIN
R ESR
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MPQ4559 can be optimized for a wide range of
capacitance and ESR values.
Compensation Components
MPQ4559 employs current mode control for easy
compensation and fast transient response. The
system stability and transient response are
controlled through the COMP pin. COMP pin is
the output of the internal error amplifier. A series
capacitor-resistor combination sets a pole-zero
combination to control the characteristics of the
control system. The DC gain of the voltage
feedback loop is given by:
A VDC R LOAD GCS A VEA
VFB
VOUT
Where AVEA is the error amplifier voltage gain,
400V/V;
GCS
is
the
current
sense
transconductance, 5.6A/V; RLOAD is the load
resistor value.
The system has two poles of importance. One is
due to the compensation capacitor (C3), the
output resistor of error amplifier. The other is due
to the output capacitor and the load resistor.
These poles are located at:
fP1
GEA
2 π C3 A VEA
fP 2
1
2 π C2 RLOAD
Where,
GEA
is
the
transconductance, 120μA/V.
error
amplifier
The system has one zero of importance, due to
the compensation capacitor (C3) and the
compensation resistor (R3). This zero is located
at:
fZ1
1
2 π C3 R3
In the case of tantalum or electrolytic capacitors,
the ESR dominates the impedance at the
switching frequency. For simplification, the output
ripple can be approximated to:
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
The system may have another zero of
importance, if the output capacitor has a large
capacitance and/or a high ESR value. The zero,
due to the ESR and capacitance of the output
capacitor, is located at:
fESR
1
2π C2 RESR
In this case, a third pole set by the compensation
capacitor (C5) and the compensation resistor
(R3) is used to compensate the effect of the ESR
zero on the loop gain. This pole is located at:
fP 3
1
2 π C5 R3
The goal of compensation design is to shape the
converter transfer function to get a desired loop
gain. The system crossover frequency where the
feedback loop has the unity gain is important.
Lower crossover frequencies result in slower line
and load transient responses, while higher
crossover frequencies could cause system
unstable. A good rule of thumb is to set the
crossover frequency to approximately one-tenth
of the switching frequency.
Table 3—Compensation Values for Typical
Output Voltage/Capacitor Combinations
VOUT
(V)
L (µH)
C2
(µF)
R3
(kΩ)
C3
(pF)
C6
(pF)
1.8
4.7
33
32.4
680
None
2.5
4.7 - 6.8
22
26.1
680
None
3.3
6.8 -10
22
68.1
220
None
5
15 - 22
33
47.5
330
None
12
10
22
16
470
2
To optimize the compensation components for
conditions not listed in Table 3, the following
procedure can be used.
Where fC is the desired crossover frequency.
2. Choose the compensation capacitor (C3) to
achieve the desired phase margin. For
applications with typical inductor values, setting
the compensation zero, fZ1, below one forth of the
crossover frequency provides sufficient phase
margin. Determine the C3 value by the following
equation:
C3
4
2 π R3 fC
3. Determine if the second compensation
capacitor (C5) is required. It is required if the
ESR zero of the output capacitor is located at
less than half of the switching frequency, or the
following relationship is valid:
f
1
S
2π C2 RESR 2
If this is the case, then add the second
compensation capacitor (C5) to set the pole fP3 at
the location of the ESR zero. Determine the C5
value by the equation:
C5
C2 RESR
R3
High Frequency Operation
The switching frequency of MPQ4559 can be
programmed up to 2MHz by an external resistor.
The minimum on time of MPQ4559 is about
100ns (typ). Pulse skipping operation can be
seen more easily at higher switching frequency
due to the minimum on time.
Since the internal bootstrap circuitry has higher
impedance, which may not be adequate to
charge the bootstrap capacitor during each
(1-D)×Ts charging period, an external bootstrap
charging diode is strongly recommended if the
switching frequency is about 2MHz (see External
Bootstrap
Diode
section
for
detailed
implementation information).
1. Choose the compensation resistor (R3) to set
the desired crossover frequency. Determine the
R3 value by the following equation:
R3
2 π C2 fC VOUT
GEA GCS
VFB
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
With higher switching frequencies, the inductive
reactance (XL) of capacitor comes to dominate,
so that the ESL of input/output capacitor
determines the input/output ripple voltage at
higher switching frequency. As a result of that,
high frequency ceramic capacitor is strongly
recommended as input decoupling capacitor and
output filtering capacitor for such high frequency
operation.
Layout becomes more important when the device
switches at higher frequency. It is essential to
place the input decoupling capacitor, catch diode
and the MPQ4559 (VIN pin, SW pin and PGND)
as close as possible, with traces that are very
short and fairly wide. This can help to greatly
reduce the voltage spike on SW node, and lower
the EMI noise level as well.
Try to run the feedback trace as far from the
inductor and noisy power traces as possible. It is
often a good idea to run the feedback trace on
the side of the PCB opposite of the inductor with
a ground plane separating the two. The
compensation components should be placed
closed to the MPQ4559. Do not place the
compensation components close to or under high
dv/dt SW node, or inside the high di/dt power
loop. If you have to do so, the proper ground
plane must be in place to isolate those. Switching
loss is expected to be increased at high switching
frequency. To help to improve the thermal
conduction, a grid of thermal vias can be created
right under the exposed pad. It is recommended
that they be small (15mil barrel diameter) so that
the hole is essentially filled up during the plating
process, thus aiding conduction to the other side.
Too large a hole can cause ‘solder wicking’
problems during the reflow soldering process.
The pitch (distance between the centers) of
several such thermal vias in an area is typically
40mil.
External Bootstrap Diode
An external bootstrap diode may enhance the
efficiency of the regulator. In below cases, an
external BST diode is recommended from the 5V
to BST pin:
There is a 5V rail available in the system;
VIN is no greater than 5V;
VOUT is between 3.3V and 5V;
This diode is also recommended for high duty
cycle operation (when VOUT/VIN > 65%)
applications.
The bootstrap diode can be a low cost one such
as IN4148 or BAT54.
Figure 2—External Bootstrap Diode
At no load or light load, the converter may
operate in pulse skipping mode in order to
maintain the output voltage in regulation. Thus
there is less time to refresh the BS voltage. In
order to have enough gate voltage under such
operating conditions, the difference of (VIN –VOUT
should be greater than 3V. For example, if the
VOUT is set to 3.3V, the VIN needs to be higher
than 3.3V+3V=6.3V to maintain enough BST
voltage at no load or light load. To meet this
requirement, EN pin can be used to program the
input UVLO voltage to VOUT+3V.
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
TYPICAL APPLICATION CIRCUITS
Figure 3—1.8V Output Typical Application Schematic
Figure 4—5V Output Typical Application Schematic
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
PCB LAYOUT GUIDE
2)
PCB layout is very important to achieve stable
operation. It is highly recommended to duplicate
EVB layout for optimum performance.
Bypass ceramic capacitors are suggested
to be put close to the VIN Pin.
3)
Ensure all feedback connections are short
and direct. Place the feedback resistors
and compensation components as close to
the chip as possible.
4)
Route SW away from sensitive analog
areas such as FB.
5)
Connect IN, SW, and especially GND
respectively to a large copper area to cool
the chip to improve thermal performance
and long-term reliability.
If change is necessary, please follow these
guidelines and take Figure 5 for reference.
1)
Keep the path of switching current short
and minimize the loop area formed by Input
cap, high-side MOSFET and external
switching diode.
MPQ4559 Typical Application Circuit
GND
R1
R5
R4
C3
R2
R3
L1
2
FB
COMP FREQ
EN
SW
VIN
BST
1
3
GND
4
SW
C4
D1
8
7
6
5
R6
C2
C1
Vin
GND
GND
Vo
TOP Layer
Bottom Layer
MPQ4559DN Layout Guide
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
PACKAGE INFORMATION
SOIC8 (EXPOSED PAD)
MPQ4559 Rev. 1.01
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MPQ4559 – 1.5A, 2MHz, 55V STEP-DOWN CONVERTER AEC-Q100 QUALIFIED
PACKAGE INFORMATION
QFN10 (3mm x 3mm) (EXPOSED PAD)
NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third
party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not
assume any legal responsibility for any said applications.
MPQ4559 Rev. 1.01
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