MP8676
4.5A, 42V, 420kHz Step-Down Converter
with Synchronizable Gate Driver
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP8676 is a monolithic step-down switch
mode converter with a built in internal power
MOSFET. It achieves 4.5A continuous output
current over a wide input supply range with
excellent load and line regulation.
Current mode operation provides fast transient
response and eases loop stabilization.
Fault condition protection includes cycle-by-cycle
current limiting and thermal shutdown.
The MP8676 requires a minimum number of
readily available standard external components
and is available in an 8-pin SOIC package with
exposed pad.
Wide 4.5V to 42V Operating Input Range
4.5A Continuous Output Current
100mΩ Internal Power MOSFET Switch
Synchronizable Gate Driver Delivers up to
95% Efficiency
Fixed 420kHz Frequency
Synchronizable up to 1.5MHz
Cycle-by-Cycle Over Current Protection with
Hiccup retry
Thermal Shutdown
Output Adjustable from 0.8V
Stable with Low ESR Output Ceramic
Capacitors
Available in a Thermally Enhanced 8-Pin
SOIC Package
APPLICATIONS
Digital Set Top Boxes
Personal Video Recorders
Broadband Communications
Flat Panel Television and Monitors
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.
TYPICAL APPLICATION
VIN
8
IN
BST
MP8676
SW
3
7
1
VOUT
3.3V
VCC
BG
OFF ON
2
EN/SYNC
FB
4
6
GND
5
MP8676 Rev.1.0
5/7/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
1
MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
ABSOLUTE MAXIMUM RATINGS (1)
PACKAGE REFERENCE
Supply Voltage VIN ....................................... 45V
VSW...................... –0.3V (–5V for < 10ns) to 46V
VBST – VSW ...................................................... 6V
All Pins ........................................... –0.3V to +6V
Junction Temperature ............................... 150C
Lead Temperature .................................... 260C
Storage Temperature .............. –65C to +150C
TOP VIEW
SW
1
8
IN
BST
2
7
EN/SYNC
VCC
3
6
FB
Recommended Operating Conditions
BG
4
5
GND
Supply Voltage VIN ........................... 4.5V to 42V
Output Voltage Range…………… 0.8V to 38V
Operating Temperature ............. –40C to +85C
EXPOSED PAD
ON BACKSIDE
*
Thermal Resistance
Part Number*
Package
Temperature
MP8676DN
SOIC8E
–40C to +85C
For Tape & Reel, add suffix –Z (eg. MP8676DN–Z)
For RoHS Compliant Packaging, add suffix –LF
(eg. MP8676DN–LF–Z)
(3)
θJA
(2)
θJC
SOIC8E .................................. 50 ...... 10... C/W
Notes:
1) Exceeding these ratings may damage the device.
2) The device is not guaranteed to function outside of its
operating conditions.
3) Measured on JESD51-7, 4-layer PCB.
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25C, unless otherwise noted.
Parameters
Feedback Voltage
Feedback Current
Switch On Resistance (4)
Switch Leakage
Current Limit (4)
Oscillator Frequency
Fold-back Frequency
Maximum Duty Cycle
Minimum On Time (4)
Under Voltage Lockout Threshold Rising
Under Voltage Lockout Threshold Hysteresis
EN Input Low Voltage
EN Input High Voltage
Symbol Condition
VFB
4.5V VIN 42V
IFB
VFB = 0.8V
RDS(ON)
VEN = 0V, VSW = 0V
IO-MAX
Duty=40%
fSW
VFB = 0.6V
VFB = 0V
VFB = 0.6V
tON
240
25
85
3.90
Typ
0.808
10
100
0.1
6.5
420
115
90
100
4.10
880
Max
0.828
10
600
205
4.30
0.4
2
VEN = 2V
VEN = 0V
EN Input Current
Sync Frequency Range (Low)
Sync Frequency Range (High)
Enable Turnoff Delay
Supply Current (Shutdown)
Supply Current (Quiescent)
Thermal Shutdown
BG Driver Bias Supply Voltage
Gate Driver Sink Impedance (4)
Gate Driver Source Impedance (4)
Gate Drive Current Sense Trip Threshold
Min
0.788
FSYNCL
FSYNCH
TOFF
VEN = 0V
VEN = 2V, VFB = 1V
VCC
RSINK
RSOURCE
VSW
ICC = 5mA
4.5
2
0.1
300
1.5
5.0
1
0.9
150
5.0
1
4
20
Units
V
nA
mΩ
μA
A
kHz
kHz
%
ns
V
mV
V
V
μA
10
1.1
KHz
MHz
μs
μA
mA
°C
V
Ω
Ω
mV
Note:
4) Guaranteed by design.
MP8676 Rev.1.0
5/7/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
2
MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
PIN FUNCTIONS
Pin #
Name
1
SW
2
3
4
5
6
7
8
Description
Switch Output.
Bootstrap. This capacitor is needed to drive the power switch’s gate above the supply
BST
voltage. It is connected between SW and BS pins to form a floating supply across the power
switch driver.
VCC
BG Driver Bias Supply. Decouple with a 1µF ceramic capacitor.
BG
Gate Driver Output. Connect this pin to the gate of the synchronous MOSFET.
Ground. This pin is the voltage reference for the regulated output voltage. For this reason
GND
care must be taken in its layout. This node should be placed outside of the M2 to C1 ground
path to prevent switching current spikes from inducing voltage noise into the part.
Feedback. An external resistor divider from the output to GND, tapped to the FB pin sets
the output voltage. To prevent current limit run away during a short circuit fault condition the
FB
frequency foldback comparator lowers the oscillator frequency when the FB voltage is
below 250mV.
EN/SYNC On/Off Control and External Frequency Synchronization Input.
Supply Voltage. The MP8676 operates from a +4.5V to +42V unregulated input. C1 is
IN
needed to prevent large voltage spikes from appearing at the input.
MP8676 Rev.1.0
5/7/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
3
MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT = 3.3V, L = 4.3µH, TA = +25ºC, unless otherwise noted.
0
Case Temperature Rise
vs. Output Current
Operating Range
Load Regulation
10
1
MP8676 Rev.1.0
5/7/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
4
MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT = 3.3V, L =4.3µH, TA = +25ºC, unless otherwise noted. (continued)
MP8676 Rev.1.0
5/7/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
5
MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
OPERATION
IN
CURRENT SENSE
AMPLIFIER
D
-+
REGULATOR
BST
EN/SYNC
REGULATOR
OSCILLATOR
420KHz
S
+
--
VCC
Q
DRIVER
R
CURRENT
LIMIT
COMPARATOR
R
SW
Q
VCC
REFERENCE
FB
VCC
+
--
ERROR
AMPLIFIER
COMP
+
--
DRIVER
PWM
COMPARATOR
BG
GND
Figure 1—Functional Block Diagram
The MP8676 is a fixed frequency, synchronous,
step-down switching regulator with an
integrated high-side power MOSFET and a gate
driver for a low-side external MOSFET. It
achieves 4.5A continuous output current over a
wide input supply range with excellent load and
line regulation. It provides a single highly
efficient solution with current mode control for
fast loop response and easy compensation.
The MP8676 operates in a fixed frequency,
peak current control mode to regulate the
output voltage. A PWM cycle is initiated by the
internal clock. The integrated high-side 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 until the next clock cycle starts. If, in
90% of one PWM period, the current in the
power MOSFET does not reach the COMP set
current value, the power MOSFET will be
forced to turn off.
MP8676 Rev.1.0
5/7/2012
Error Amplifier
The error amplifier compares the FB pin voltage
with the internal 0.8V reference (REF) and
outputs a current proportional to the difference
between the two. This output current is then
used to charge or discharge the internal
compensation network to form the COMP
voltage, which is used to control the power
MOSFET current. The optimized internal
compensation network minimizes the external
component counts and simplifies the control
loop design.
Internal Regulator
Most of the internal circuitries are powered from
the 5V internal regulator. This regulator takes
the VIN input and operates in the full VIN range.
When VIN is greater than 5.0V, the output of
the regulator is in full regulation. When VIN is
lower than 5.0V, the output decreases. Since
this internal regulator provides the bias current
for the bottom gate driver that requires
significant amount of current depending upon
the external MOSFET selection, a 1µF ceramic
capacitor for decoupling purpose is required.
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© 2012 MPS. All Rights Reserved.
6
MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
Enable/Synch Control
The MP8676 has a dedicated Enable/Synch
control pin (EN/SYNC). By pulling it high or low,
the IC can be enabled and disabled by EN. Tie
EN to VIN for automatic start up. To disable the
part, EN must be pulled low for at least 5µs.
The MP8676 can be synchronized to external
clock range from 300kHz up to 1.5MHz through
the EN/SYNC pin. The internal clock rising
edge is synchronized to the external clock rising
edge.
Under-Voltage Lockout (UVLO)
Under-voltage lockout (UVLO) is implemented
to protect the chip from operating at insufficient
supply voltage. The MP8676 UVLO comparator
monitors the output voltage of the internal
regulator, VCC. The UVLO rising threshold is
about 4.1V while its falling threshold is a
consistent 3.2V.
Internal Soft-Start
The soft-start is implemented to prevent the
converter output voltage from overshooting
during startup. When the chip starts, the
internal circuitry generates a soft-start voltage
(SS) ramping up from 0V to 1.2V. 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.
Over-Current-Protection (OCP)
The MP8676 has cycle-by-cycle over current
limit when the inductor current peak value
exceeds the set current limit threshold.
Meanwhile, output voltage starts to drop until
FB is below the Under-Voltage (UV) threshold,
typically 30% below the reference. Once a
output UV is triggered, the MP8676 enters
hiccup mode, which is especially useful to
ensure system safety under fault condition. The
MP8676 exits the hiccup mode once the EN or
input power is re-cycled.
MP8676 Rev.1.0
5/7/2012
Thermal Shutdown
Thermal shutdown is implemented to prevent
the chip from operating at exceedingly high
temperatures. When the silicon die temperature
is higher than 150C, it shuts down the whole
chip. When the temperature is lower than its
lower threshold, typically 140C, the chip is
enabled again.
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 bootstrap capacitor
voltage is regulated internally by VIN through D1,
M3, C4, L1 and C2 (Figure 2). If (VIN-VSW) is
more than 5V, U2 will regulate M3 to maintain a
5V BST voltage across C4.
D1
VIN
M3
+
5V
+
--
BST
U2
--
C4
VOUT
SW
L1
C2
Figure 2—Internal Bootstrap Charging
Circuit
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.
Three events can shut down the chip: EN low,
VIN low and thermal shutdown. In the shutdown
procedure, the signaling path is first blocked to
avoid any fault triggering. The COMP voltage
and the internal supply rail are then pulled
down. The floating driver is not subject to this
shutdown command.
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
7
MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
APPLICATION INFORMATION
The schematic on the front page shows a typical
MP8676 application. The IC can provide up to
4.5A output current at a nominal output voltage
of 3.3V. For proper thermal performance, the
exposed pad of the device must be soldered
down to the printed circuit board.
Synchronous MOSFET
The external synchronous MOSFET is used to
freewheel the inductor current when the internal
high-side switch is off. It significantly reduces
the power loss compared against a Schottky
rectifier.
Setting the Output Voltage
The external resistor divider is used to set the
output voltage (see the schematic on front
page). The feedback resistor R1 also sets the
feedback loop bandwidth with the internal
compensation capacitor (see Figure 1). Choose
R1 to be around 40.2kΩ for optimal transient
response. R2 is then given by:
Selecting the Input Capacitor
The input capacitor (C1) reduces the surge
current drawn from the input and the switching
noise from the device. The input capacitor
impedance at the switching frequency should
be less than the input source impedance to
prevent high frequency switching current from
passing to the input. Ceramic capacitors with
X5R
or
X7R
dielectrics
are
highly
recommended because of their low ESR and
small temperature coefficients. For 4.5A output
applications, a 22µF capacitor is sufficient.
R2
R1
VOUT
1
0 .8 V
Table 1—Resistor Selection for Common
Output Voltages
VOUT (V)
1.8
2.5
3.3
5
R1 (kΩ)
40.2 (1%)
40.2 (1%)
40.2 (1%)
40.2 (1%)
R2 (kΩ)
32.4 (1%)
19.1 (1%)
13 (1%)
7.68 (1%)
Selecting the Output Capacitor
The output capacitor (C2) keeps output voltage
small and ensures regulation loop stability. The
output capacitor impedance should be low at
the switching frequency. Ceramic capacitors
with X5R or X7R dielectrics are recommended.
Selecting the Inductor
A 1µH to 10µH inductor with a DC current rating
of at least 25% higher than the maximum load
current is recommended for most applications.
For highest efficiency, the inductor DC
resistance should be less than 15mΩ. For most
designs, the inductance value can be derived
from the following equation.
L
VOUT ( VIN VOUT )
VIN IL f OSC
Where ΔIL is the inductor ripple current.
Choose inductor ripple current to be approximately
30% of the maximum load current, 4.5A. The
maximum inductor peak current is:
IL(MAX ) ILOAD
I L
2
Under light load conditions below 100mA, larger
inductance is recommended for improving
efficiency.
MP8676 Rev.1.0
5/7/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
8
MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
PCB Layout Guide
PCB layout is very important to achieve stable
operation. Please follow these guidelines and
take Figure3 for references.
1)
Keep the path of switching current short
and minimize the loop area formed by Input
cap, high-side and low-side MOSFETs.
2)
Keep the connection of low-side MOSFET
between SW pin and input power ground
as short and wide as possible.
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.
SGND
LGATE
GND
R1
FB
BST
IN
SW
8
Rb
7
6
Bottom Layer
Figure 3—PCB Layout
External Bootstrap Diode
An external bootstrap diode may enhance the
efficiency of the regulator, the applicable
conditions of external BST diode are:
VOUT=5V or 3.3V; and
Duty cycle is high: D=
C3
VCC
EN
SGND
In these cases, an external BST diode is
recommended from the output of the voltage
regulator to BST pin, as shown in Fig.4
5
C1
L1
External BST Diode
IN4148
BST
MP8676
1
2
3
SW
4
PGND
C2
Top Layer
VOUT
>65%
VIN
CBST
L
5V or 3.3V
COUT
Figure 4—Add Optional External Bootstrap
Diode to Enhance Efficiency
The recommended external BST diode is
IN4148, and the BST cap is 0.1~1µF.
MP8676 Rev.1.0
5/7/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
9
MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER
PACKAGE INFORMATION
SOIC8E (EXPOSED PAD)
0.189(4.80)
0.197(5.00)
0.124(3.15)
0.136(3.45)
8
5
0.150(3.80)
0.157(4.00)
PIN 1 ID
1
0.228(5.80)
0.244(6.20)
0.089(2.26)
0.101(2.56)
4
TOP VIEW
BOTTOM VIEW
SEE DETAIL "A"
0.051(1.30)
0.067(1.70)
SEATING PLANE
0.000(0.00)
0.006(0.15)
0.013(0.33)
0.020(0.51)
0.0075(0.19)
0.0098(0.25)
SIDE VIEW
0.050(1.27)
BSC
FRONT VIEW
0.010(0.25)
x 45o
0.020(0.50)
GAUGE PLANE
0.010(0.25) BSC
0.050(1.27)
0.024(0.61)
0o-8o
0.016(0.41)
0.050(1.27)
0.063(1.60)
DETAIL "A"
0.103(2.62)
0.138(3.51)
RECOMMENDED LAND PATTERN
0.213(5.40)
NOTE:
1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN
BRACKET IS IN MILLIMETERS.
2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS OR GATE BURRS.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH
OR PROTRUSIONS.
4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING)
SHALL BE 0.004" INCHES MAX.
5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION BA.
6) DRAWING IS NOT TO SCALE.
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.
MP8676 Rev. 1.0
5/7/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
10
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