MP8668
8A, 21V, 600KHz Step-Down Converter
with Synchronizable Gate Driver
The Future of Analog IC Technology
DESCRIPTION
The MP8668 is a monolithic step-down switch
mode converter with a built in internal power
MOSFET. It achieves 8A 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 MP8668 requires a minimum number of
readily available standard external components
and is available in a space saving 3mm x 4mm
14-pin QFN package.
FEATURES
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Wide 4.5V to 21V Operating Input Range
8A Continuous Output Current
42mΩ Internal Power MOSFET Switch
Power Good Indicator
Synchronous Gate Driver Delivers up to
95% Efficiency
Fixed 600KHz Frequency
Synchronizable Up to 1.5MHz
Cycle-by-Cycle Over Current Protection with
Hiccup
Thermal Shutdown
Output Adjustable from 0.8V
Stable with Low ESR Output Ceramic
Capacitors
Available in a 3mm x 4mm 14-Pin QFN
Package
Point of Load Regulator in Distributed
Power System
Digital Set Top Boxes
Personal Video Recorders
Broadband Communications
Flat Panel Television and Monitors
APPLICATIONS
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“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
V
IN
4, 5, 6
C1
22uF
25V
12
IN
BST
11
Efficiency vs
Output Current
C4
100nF L1
16V
2.2uH
100
EFFICIENCY (%)
C3
1uF
16V
PGOOD
3.3V
OFF ON
VCC
SW
8, 9, 10
V
OUT
3.3V
V
IN
=12V
90
V
IN
=20V
MP8668
2
PG
BG
13
M2
C2
100uF
6.3V
80
V
OUT
=3.3V
70
1
2
3 4
5
6
7
OUTPUT CURRENT (A)
8
3
EN/SYNC
GND
14
FB
1
MP8668 Rev. 1.1
11/12/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
1
MP8668 – 8A, 21V, 600KHz STEP-DOWN WITH SYNCHRONOUS GATE DRIVER
PACKAGE REFERENCE
TOP VIEW
FB
PG
EN/SYNC
IN
IN
IN
N/C
1
2
3
4
5
6
7
14
13
12
11
10
9
8
GND
BG
VCC
BST
SW
SW
SW
ABSOLUTE MAXIMUM RATINGS
(1)
Supply Voltage V
IN
....................................... 23V
V
SW
............................................................... 24V
V
BS
-V
SW
......................................................... 6V
All Other Pins................................. –0.3V to +6V
Junction Temperature...............................150°C
Lead Temperature ....................................260°C
Storage Temperature ..............–65°C to +150°C
Recommended Operating Conditions
Thermal Resistance
(3)
(2)
Supply Voltage V
IN
........................... 4.5V to 21V
Operating Temperature .............–40°C to +85°C
3x4 QFN14 ............................. 48 ...... 11...
°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 approximately 1” square of 1 oz copper.
EXPOSED PAD
ON BACKSIDE
θ
JA
θ
JC
Part Number*
MP8668DL
*
Package
3x4 QFN14
Temperature
–40°C to +85°C
For Tape & Reel, add suffix –Z (eg. MP8668DL–Z)
For RoHS Compliant Packaging, add suffix –LF
(eg. MP8668DL–LF–Z)
ELECTRICAL CHARACTERISTICS
V
IN
= 12V, T
A
= +25°C, 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
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
Power Good Threshold Rising
Power Good Threshold Hysteresis
PG Pin Level
Note:
4) Guaranteed by design.
MP8668 Rev. 1.1
11/12/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
Symbol Condition
V
FB
4.5V
≤
V
IN
≤
21V
I
FB
V
FB
= 0.8V
R
DS(ON)
V
EN
= 0V, V
SW
= 0V
f
SW
t
ON
V
FB
= 0.6V
V
FB
= 0V
V
FB
= 0.6V
Min
0.788
Typ
0.808
10
42
0
600
150
90
100
4.1
880
2
0
300
1.5
5.0
1
0.9
150
5
1
4
20
0.74
40
Max
0.828
10
800
240
4.3
0.4
9.5
400
60
85
3.9
1.2
Units
V
nA
mΩ
µA
A
KHz
KHz
%
ns
V
mV
V
V
µA
KHz
MHz
us
µA
mA
°C
V
Ω
Ω
mV
V
mV
V
V
EN
= 2V
V
EN
= 0V
F
SYNCL
F
SYNCH
T
OFF
V
EN
=
0V
V
EN
=
2V, V
FB
= 1V
V
CC
R
SINK
R
SOURCE
4.5
10
1.1
0.69
V
PG
PG Sink 4mA
0.79
0.4
2
MP8668 – 8A, 21V, 600KHz STEP-DOWN WITH SYNCHRONOUS GATE DRIVER
PIN FUNCTIONS
Pin #
1
Description
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
FB
the frequency foldback comparator lowers the oscillator frequency when the FB voltage is
below 250mV.
Power Good Indicator. The output of this pin is low if the output voltage is 10% less than
PG
the nominal voltage, otherwise it is an open drain.
EN/SYNC On/Off Control and External Frequency Synchronization Input.
Supply Voltage. The MP8668 operates from a +4.5V to +21V unregulated input. C1 is
IN
needed to prevent large voltage spikes from appearing at the input.
N/C
No Connect.
SW
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 BST 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 synchronous MOSFET Gate.
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.
Name
2
3
4, 5, 6
7
8, 9, 10
11
12
13
14
MP8668 Rev. 1.1
11/12/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
3
MP8668 – 8A, 21V, 600KHz STEP-DOWN WITH SYNCHRONOUS GATE DRIVER
TYPICAL PERFORMANCE CHARACTERISTICS
V
IN
= 12V, V
OUT
= 3.3V, L = 2.2µH, T
A
= +25ºC, unless otherwise noted.
Efficiency vs
Output Current
100
V
IN
=12V
EFFICIENCY (%)
V
OUT
1V/div.
PG
5V/div.
V
SW
20V/div.
V
OUT
2V/div.
V
SW
10V/div.
V
IN
10V/div.
Hiccup with Output
Short Circuit
Power up
No Load
90
V
IN
=20V
80
V
OUT
=3.3V
70
1
2
3 4
5
6
7
OUTPUT CURRENT (A)
8
I
L
5A/div.
I
L
5A/div.
400us/div.
2ms/div.
Startup through Enable
No Load
V
OUT
2V/div.
Startup through Enable
I
OUT
= 8A (Resistive Load)
Input Ripple Voltage
I
OUT
= 8A
V
OUT
2V/div.
V
SW
10V/div.
V
EN
10V/div.
I
L
5A/div.
V
SW
5V/div.
V
SW
10V/div.
V
EN
10V/div.
I
L
5A/div.
V
IN,AC
200mV/div.
2ms/div.
2ms/div.
1us/div.
Output Ripple Voltage
I
OUT
= 8A
Load Transient Response
100
80
MAGNITUDE (dB)
Close Loop Bode Plot
100
80
Phase
40
20
Magitude
0
-20
-40
-60
-80
10k
100k
-100
PHASE (degree)
60
40
20
0
-20
-40
-60
-80
60
V
SW
5V/div.
V
OUT,AC
200mV/div.
V
SW
10V/div.
V
OUT, AC
20mV/div.
I
OUT
5A/div.
1us/div.
100us/div.
-100
1k
MP8668 Rev. 1.1
11/12/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
4
MP8668 – 8A, 21V, 600KHz STEP-DOWN WITH SYNCHRONOUS GATE DRIVER
TYPICAL PERFORMANCE CHARACTERISTICS
(continued)
V
IN
= 12V, V
OUT
= 2.5V, L = 2.2µH, T
A
= +25ºC, unless otherwise noted.
Enabled Supply Current
vs Input Voltage
0.45
0.40
1100
1050
1000
950
900
0
5
10
15
20
INPUT VOLTAGE (V)
25
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
0
5
10
15
20
INPUT VOLTAGE (V)
25
V
CC
(V)
1150
Disabled Supply Current
vs Input Voltage
4.9
4.7
4.5
4.3
4.1
3.9
3.7
3.5
V
CC
Regulator Line
Regulation
0
5
10
15
20
INPUT VOLTAGE (V)
25
Case Temperature Rise
vs Output Current
CASE TEMPERATURE RISE (
O
C)
Operating Range
NORMALIZED OUTPUT VOLTAGE
Load Regulation
1.001
V
IN
=20V
1.000
0.999
V
IN
=12V
0.998
0.997
0.996
40
35
30
25
20
15
10
5
0
0
2
4
6
8
OUTPUT CURRENT (A)
10
OUTPUT VOLTAGE (V)
100
V
O_MAX
SPEC
10
D
MAX
Limit
1.4MHz
1MHz
1
V
FB_MIN
600KHz
0.1
0
5
10
15
20
INPUT VOLTAGE (V)
25
0
1
2 3 4 5 6 7 8 9 10
OUTPUT CURRENT (A)
Line Regulation
I
OUT
= 8A
NORMALIZED OUTPUT VOLTAGE
Peak Current vs.
Duty Cycle
12
PEAK CURRENT (A)
1.002
1.001
1.000
0.999
0.998
0.997
0.996
0.995
5
7
9 11 13 15 17 19 21
INPUT VOLTAGE (V)
10
8
6
4
2
0
10
30
50
70
DUTY CYCLE (%)
90
MP8668 Rev. 1.1
11/12/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
5
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