MPS MP2377 3a, 21v, 600khz step-down converter Datasheet

MP2377
3A, 21V, 600kHz
Step-Down Converter
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP2377 is a monolithic step-down switch
mode converter with a built in high-side power
MOSFET. It achieves 3A 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 current limiting
and thermal shutdown.
The MP2377 requires a minimum number of
readily available standard external components
and is available in 8-pin SOIC packages with
exposed pad.
•
•
Wide 4.5V to 21V Operating Input Range
3A Output Current
100mΩ Internal Power MOSFET Switch
Power Good Indicator
Fixed 600kHz Frequency
Synchronizable to >1MHz External Clock
Over Current Latch Off Protection
Thermal Shutdown
Output Adjustable from 0.81V
Stable with Low ESR Output Ceramic
Capacitors
Available in Thermally Enhanced 8-Pin
SOIC Packages
Supports Soft-Start into Pre-Biased Output
APPLICATIONS
•
•
•
Distributed Power Systems
Battery Charger
Pre-Regulator for Linear Regulators
“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
VIN
8
IN
BST
Efficiency vs
Load Current
2
100
80
VCC
MP2377
POWER
GOOD
OFF ON
6
7
PG
EN/SYNC
FB
GND
4
MP2377 Rev. 0.92
4/19/2011
SW
1
5
EFFICIENCY (%)
3
VIN=5V
VIN=12V
60
40
20
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
LOAD CURRENT (A)
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MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
ABSOLUTE MAXIMUM RATINGS (1)
PACKAGE REFERENCE
Supply Voltage VIN ....................................... 23V
VSW......................... -0.3V(-5V for < 10ns) to 24V
VBST - VSW .................................................... + 6V
All Other Pins ................................. –0.3V to +6V
Junction Temperature ............................... 150°C
Lead Temperature .................................... 260°C
Storage Temperature .............. –65°C to +150°C
TOP VIEW
SW
1
8
IN
BST
2
7
EN/SYNC
VCC
3
6
PG
GND
4
5
FB
Recommended Operating Conditions
Supply Voltage VIN ........................... 4.5V to 21V
Operating Temperature ............. –40°C to +85°C
EXPOSED PAD
ON BACKSIDE
Thermal Resistance
(3)
θJA
θJC
SOIC8 ..................................... 90 ...... 45... °C/W
SOIC8E .................................. 50 ...... 10... °C/W
Part Number*
Package
Temperature
MP2377DN
SOIC8E
–40°C to +85°C
*
(2)
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.
For Tape & Reel, add suffix –Z (eg. MP2377DN–Z)
For RoHS Compliant Packaging, add suffix –LF
(eg. MP2377DN–LF–Z)
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameters
Feedback Voltage
Symbol
VFB
Feedback Current
IFB
(4)
Switch On Resistance
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
Min
0.788
RDS(ON)
VEN = 0V, VSW = 0V
Typ
0.808
10
2
100
0.1
Max
0.828
10
4
fSW
VFB = 0.6V
VFB = 0V
VFB = 0.6V
85
tON
3.9
600
150
90
100
4.1
880
4.3
0.4
1.2
VEN = 2V
VEN = 0V
VEN = 0V
VEN = 2V, VFB = 1V
EN Input Current
Supply Current (Shutdown)
Supply Current (Quiescent)
Thermal Shutdown
Bias Supply
Power Good Threshold Rising
Power Good Threshold Hysteresis
PG Pin Level
Sync Frequency Range (Low)
Sync Frequency Range (High)
Enable Turnoff Delay
Condition
4.5V ≤ VIN ≤ 21V
VFB = 0.8V
VFB = 2V
VCC
VPG
FSYNCL
FSYNCH
TOFF
ICC = 5mA
4.5
2
0.01
0.1
0.9
150
5.0
0.74
40
PG Sink 4mA
µA
0.4
300
1.5
5.0
Units
V
nA
µA
mΩ
µA
A
KHz
KHz
%
ns
V
mV
V
V
µA
mA
°C
V
V
mV
V
KHz
MHz
µS
Note:
4) Guaranteed by design.
MP2377 Rev. 0.92
4/19/2011
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MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
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
Bias Supply. Decouple this pin with a 1µF ceramic capacitor.
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 D1 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.
Power Good Indicator. Connect this pin to VCC or VOUT by a 100kΩ pull-up resistor. The
output of this pin is low if the output voltage is 10% less than the nominal voltage, otherwise
PG
it is an open drain.
EN/SYNC On/Off Control Input and Synchronization Pin.
Supply Voltage. The MP2377 operates from a +4.5V to +21V unregulated input. C1 is
IN
needed to prevent large voltage spikes from appearing at the input.
MP2377 Rev. 0.92
4/19/2011
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MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT = 3.3V, L = 3.3µH, TA = +25ºC, unless otherwise noted.
Efficiency vs
Load Current
Efficiency vs
Load Current
VO = 3.3V, IOUT = 3A
IOUT = 3A
100
80
VIN=12V
EFFICIENCY (%)
EFFICIENCY (%)
80
60
40
20
0
100
VIN=5V
VOUT
10mV/div.
60
VSW
10V/div.
40
20
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
LOAD CURRENT (A)
VIN=12V
VOUT=5V
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
LOAD CURRENT (A)
Steady States
Steady States
VIN = 12V, VO = 3.3V, IOUT = 0=1.5A
VIN = 12V, VO = 3.3V, IOUT = 3A
VOUT
10mV/div.
I indutor
1A/div.
VEN
5V/div.
VOUT
10mV/div.
VOUT
2V/div.
VSW
10V/div.
VSW
10V/div.
I indcutor
1A/div.
I inductor
2A/div.
VSW
10V/div.
VEN
5V/div.
VEN
5V/div.
VOUT
2V/div.
VOUT
2V/div.
VSW
10V/div.
VSW
10V/div.
I inductor
1A/div.
I inductor
2A/div.
MP2377 Rev. 0.92
4/19/2011
1ms/div.
I inductor
2A/div.
1ms/div.
VEN
5V/div.
VOUT
2V/div.
VSW
10V/div.
I inductor
1A/div.
1ms/div.
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1ms/div.
4
MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT = 3.3V, L = 3.3µH, TA = +25ºC, unless otherwise noted.
VEN
5V/div.
VEN
5V/div.
VOUT
2V/div.
VOUT
2V/div.
VSW
10V/div.
VSW
10V/div.
I inductor
1A/div.
I inductor
2A/div.
1ms/div.
Load Regulation
I inductor
2A/div.
Peak Current vs Duty Cycle
VIN=12V, VOUT=3.3V
0.00%
VIN=5V, VOUT=3.3V
VIN=23V VOUT=3.3V
-1.00%
0.00
1.00
2.00
LOAD CURRENT (A)
3.00
8
0.50%
0.00%
IOUT=1.5A
-0.50%
-1.00%
0.00
5.00 10.00 15.00 20.00 25.00
INPUT VOLTAGE (V)
PEAK CURRENT (%)
0.50%
LINE REGULATION (%)
1.00%
-0.50%
2ms/div.
Line Regulation
1.00%
LOAD REGULATION (%)
VOUT
2V/div.
VSW
10V/div.
6
4
2
0
10% 20% 30% 40% 50% 60% 70%
CYCLE DUTY (%)
Load Transient
VO/AC
50mV/div.
I_inductor
2A/div.
MP2377 Rev. 0.92
4/19/2011
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MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
OPERATION
IN
CURRENT SENSE
AMPLIFIER
D2
+
--
x40
REGULATOR
BST
EN/SYNC
OSCILLATOR
600KHz
REGULATOR
S
+
--
VCC
Q
DRIVER
R
CURRENT
LIMIT
COMPARATOR
SW
R
REFERENCE
0.81 VREF
FB
PG
+
--
ERROR
AMPLIFIER
+
--
PWM
COMPARATOR
POWER
GOOD
GND
Figure 1—Functional Block Diagram
The MP2377 is a fixed frequency, step-down
switching regulator with an integrated high-side
power MOSFET. It achieves 3A 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 MP2377 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.
Power Good Indicator
When the FB is below 0.74V, the PG pin will be
internally pulled low. When the FB is above
0.74V, the PG becomes an open-drain output.
MP2377 Rev. 0.92
4/19/2011
Error Amplifier
The error amplifier compares the FB pin voltage
with the internal 0.808V 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 1uF ceramic
capacitor for decoupling purpose is required.
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MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
Enable/Synch Control
The MP2377 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 MP2377 can be synchronized to external
clock range from 300KHz up to 1.4MHz 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 MP2377 UVLO comparator
monitors the output voltage of the internal
regulator, VCC. The UVLO rising threshold is
about 4.0V while its falling threshold is about
3.6V.
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 and Latchoff
The MP2377 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 UV
is triggered, the MP2377 is latched off until En
or IN is recycled. This protection mode is
especially useful when the output is dead-short
to ground.
Thermal Shutdown
Thermal shutdown is implemented to prevent
the chip from operating at exceedingly high
temperatures. When the silicon die temperature
is higher than 150°C, it shuts down the whole
chip. When the temperature is lower than its
lower threshold, typically 140°C, 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 (Figure 2). Even
at no load condition, as long as VIN is 3V higher
than VOUT, C4 will have enough voltage
provided by VIN through D2, M2 C4, L1 and C2.
If (VIN-VSW) is more than 5V, U2 will regulate M2
to maintain a 5V BST voltage across C4.
+
+
--
--
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.
MP2377 Rev. 0.92
4/19/2011
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MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
APPLICATION INFORMATION
The schematic on the front page shows a typical
MP2377 application. The IC can provide up to
3A 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.
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:
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 Inductor
A 1µH to 10µH inductor with a DC current rating
of at least 25% percent 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
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
Diode
Voltage/Current
Rating
Manufacture
B330
MBRS330
30V, 3A
30V, 3A
Diodes Inc.
On Semi
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 3A output
applications, a 10µF capacitor is sufficient.
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.
Where ∆IL is the inductor ripple current.
Choose inductor current to be approximately
30% of the maximum load current, 3A. The
maximum inductor peak current is:
IL(MAX ) = ILOAD +
∆I L
2
Under light load conditions below 100mA, larger
inductance is recommended for improved efficiency.
MP2377 Rev. 0.92
4/19/2011
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MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
PCB Layout Guide
PCB layout is very important to achieve stable
operation. Please follow these guidelines and
take Figure3 and 4 for references.
1) Keep the path of switching current short
and minimize the loop area formed by Input
cap, high-side MOSFET and schottky diode.
Keep the connection of schottky diode
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. For single layer
PCB, exposed pad should not be soldered.
Top Layer
4
3
Cb
2
1
C3
5
6
7
8
R3
R2
2)
Bottom Layer
Figure 4—PCB Layout for Double Layers
Figure 3—PCB Layout for Single Layer
MP2377 Rev. 0.92
4/19/2011
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MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
External Bootstrap Diode
An external bootstrap diode may enhance the
efficiency of the regulator, the applicable
conditions of external BST diode are:
z
VOUT=5V or 3.3V; and
z
Duty cycle is high: D=
VOUT
>65%
VIN
In these cases, an external BST diode is
recommended from the output of the voltage
regulator to BST pin, as shown in Fig.5
MP2377 Rev. 0.92
4/19/2011
External BST Diode
IN4148
BST
MP2377
SW
CBST
L
5V or 3.3V
COUT
Figure 5—Add Optional External Bootstrap
Diode to Enhance Efficiency
The recommended external BST diode is
IN4148, and the BST cap is 0.1~1µF.
By using this circuit, 5V input voltage can output
3.3V and 2.5V with just 30mA load.
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MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER
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
MP2377 Rev. 0.92
4/19/2011
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.
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