The Future of Analog IC Technology
TM
TM
MP2359
1.2A, 24V, 1.4MHz
Step-Down Converter in a TSOT23-6
DESCRIPTION
The MP2359 is a monolithic step-down switch
mode converter with a built-in power MOSFET.
It achieves 1.2A peak 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
thermal
shutdown.
The MP2359 requires a minimum number of
readily available standard external components.
The MP2359 is available in TSOT23-6 and
SOT23-6 packages.
EVALUATION BOARD REFERENCE
Dimensions
limiting and
Board Number
EV2359DJ-00B
2.1”X x 1.9”Y x 0.4”Z
FEATURES
• 1.2A Peak Output Current
• 0.35Ω Internal Power MOSFET Switch
• Stable with Low ESR Output Ceramic
Capacitors
• Up to 92% Efficiency
• 0.1µA Shutdown Mode
• Fixed 1.4MHz Frequency
• Thermal Shutdown
• Cycle-by-Cycle Over Current Protection
• Wide 4.5V to 24V Operating Input Range
• Output Adjustable from 0.81V to 15V
• Available
Packages
in TSOT23-6 and SOT23-6
APPLICATIONS
• Distributed Power Systems
• Battery Charger
• Pre-Regulator for Linear Regulators
• WLED Drivers
“MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic
Power Systems, Inc.
TYPICAL APPLICATION
VIN
12V
5
IN
BST
OFF ON
4
EN
MP2359 SW
FB
GND
2
1
6
3
CB
10nF
D1
B230A
VOUT
3.3V @ 1.2A
Efficiency vs
Load Currents
VIN = 12V
)
%
(
I
Y
C
N
E
C
F
F
E
I
100
90
80
70
60
50
40
30
20
10
0
0.01
VIN = 24V
VOUT = 5V
0.1
1
LOAD CURRENT (A)
MP2359 Rev. 1.1
6/23/2006
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© 2006 MPS. All Rights Reserved.
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1
PACKAGE REFERENCE
TOP VIEW
TM
BST
GND
FB
1
2
3
SW
MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6
ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage VIN....................................... 26V
VSW....................................... –0.3V to VIN + 0.3V
VBS ....................................................... VSW + 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 (2)
Supply Voltage VIN........................... 4.5V to 24V
Output Voltage VOUT ...................... 0.81V to 15V
Ambient Temperature................–40°C to +85°C
Thermal Resistance (3)
TSOT23-6.............................. 220.... 110.. °C/W
SOT23-6 ................................ 220.... 110.. °C/W
θJC
θJA
EN
6
5
4
IN
Notes:
1) Exceeding these ratings may damage the device.
2) The device function is not guaranteed outside of the
recommended operating conditions.
3) Measured on approximately 1” square of 1 oz copper.
Max Units
0.830
V
µA
Ω
µA
A
10
1.7
3.1
0.4
1.0
1.0
MHz
KHz
%
ns
V
mV
V
V
µA
µA
mA
°C
2
Part Number*
MP2359DJ
MP2359DT
Package
TSOT23-6
SOT23-6
Temperature
–40°C to +85°C
–40°C to +85°C
* For Tape & Reel, add suffix –Z (eg. MP2359DJ–Z)
For RoHS compliant packaging, add suffix –LF (eg.
MP2359DJ–LF–Z)
VFB
IFB
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +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
fSW
tON
RDS(ON)
EN Input Current
Supply Current (Shutdown)
Supply Current (Quiescent)
Thermal Shutdown (4)
Note:
4) Guaranteed by design.
IS
IQ
Symbol Condition
4.5V ≤ VIN ≤ 24V
VFB = 0.8V
VEN = 0V, VSW = 0V
VFB = 0.6V
VFB = 0V
VFB = 0.6V
VEN = 2V
VEN = 0V
VEN = 0V
VEN = 2V, VFB = 1V
Min
0.790
1.2
2.5
1.2
Typ
0.810
0.1
0.35
1.8
1.4
460
87
100
2.8
150
2.1
0.1
0.1
0.8
150
MP2359 Rev. 1.1
6/23/2006
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
www.MonolithicPower.com
© 2006 MPS. All Rights Reserved.
TM
MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6
PIN FUNCTIONS
Pin # Name Description
BST
GND
FB
Bootstrap. A capacitor is connected between SW and BS pins to form a floating supply across
the power switch driver. This capacitor is needed to drive the power switch’s gate above the
supply voltage.
Ground. This pin is the voltage reference for the regulated output voltage. For this reason 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
frequency foldback comparator lowers the oscillator frequency when the FB voltage is below
250mV.
EN On/Off Control Input. Pull EN above 1.2V to turn the device on.
IN
Supply Voltage. The MP2359 operates from a +4.5V to +24V unregulated input. C1 is needed
to prevent large voltage spikes from appearing at the input.
SW Switch Output.
1
2
3
4
5
6
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT = 3.3V, L = 4.7µH, C1 = 10µF, C2 = 22µF, TA = +25ºC, unless otherwise noted.
100
90
80
70
60
50
40
30
20
10
0
0.01
0.820
0.818
0.816
0.814
0.812
0.810
0.808
0.806
0.804
0.802
0.800
)
%
(
I
Y
C
N
E
C
F
F
E
I
)
V
(
E
G
A
T
L
O
V
K
C
A
B
D
E
E
F
MP2359 Rev. 1.1
6/23/2006
Efficiency vs
Load Current
VIN = 12V
)
%
(
I
Y
C
N
E
C
F
F
E
I
100
90
80
70
60
50
40
30
20
10
0
0.01
VIN = 24V
VOUT = 5V
0.1
1
LOAD CURRENT (A)
10
Switching Frequency vs
Die Temperature
(
z
H
M
) 1.50
1.48
1.46
1.44
1.42
1.40
1.38
1.36
1.34
1.32
1.30
Y
C
N
E
U
Q
E
R
F
G
N
H
C
T
W
S
I
I
-50 -25 0 25
75 100 125
DIE TEMPERATURE (OC)
50
Efficiency vs
Load Current
VIN = 18V
VIN = 24V
VOUT = 2.5V
0.1
1
LOAD CURRENT ( A)
Feedback Voltage vs
Die Temperature
10
150
-50 -25 0 25
75 100 125
DIE TEMPERATURE (OC)
50
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3
TM
MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 12V, VOUT = 3.3V, L = 4.7µH, C1 = 10µF, C2 = 22µF, TA = +25ºC, unless otherwise noted.
)
A
I
I
(
T
M
L
T
N
E
R
R
U
C
Current Limit vs
Duty Cycle
Steady State Test
IOUT = 0.5A
VOUT
AC Coupled
50mV/div.
IL
1A/div.
ILOAD
1A/div.
VOUT
20mV/div.
VSW
10V/div.
IL
500mA/div.
3.0
2.5
2.0
1.5
1.0
0.5
0
0
20
40
60
80
100
DUTY CYCLE (%)
Short Circuit Entry
Short Circuit Recovery
Start-up through Enable
No Load
400ns/div.
VOUT
1V/div.
IL
1A/div.
VEN
5V/div.
VOUT
1V/div.
VSW
10V/div.
IL
500mA/div.
Start-up through Enable
IOUT = 1A Resistive Load
Shut-down through Enable
No Load
Shut-down through Enable
IOUT = 1A Resistive Load
VEN
5V/div.
VOUT
2V/div.
VSW
10V/div.
IL
1A/div.
VEN
5V/div.
VOUT
2V/div.
VSW
10V/div.
IL
1A/div.
VOUT
1V/div.
IL
1A/div.
VEN
5V/div.
VOUT
1V/div.
VSW
10V/div.
IL
1A/div.
MP2359 Rev. 1.1
6/23/2006
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
www.MonolithicPower.com
© 2006 MPS. All Rights Reserved.
4
TM
MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6
OPERATION
The MP2359 is a current mode buck regulator.
That is, the EA output voltage is proportional to
the peak inductor current.
At the beginning of a cycle, M1 is off. The EA
output voltage is higher than the current sense
amplifier output, and the current comparator’s
output is low. The rising edge of the 1.4MHz
CLK signal sets the RS Flip-Flop. Its output
turns on M1 thus connecting the SW pin and
inductor to the input supply.
The increasing inductor current is sensed and
amplified by the Current Sense Amplifier. Ramp
compensation is summed to the Current Sense
Amplifier output and compared to the Error
Amplifier output by the PWM Comparator.
When the sum of the Current Sense Amplifier
output and the Slope Compensation signal
exceeds the EA output voltage, the RS Flip-
Flop is reset and M1 is turned off. The external
Schottky rectifier diode (D1) conducts
the
inductor current.
IN
5
RAMP
GENERATOR
EN
4
REGULATOR
OSCILLATOR
1.4MHz/460KHz
REFERENCE
FB
GND
3
2
1pF
27pF
+
EA--
AMPLIFIER
ERROR
If the sum of the Current Sense Amplifier output
and the Slope Compensation signal does not
exceed the EA output for a whole cycle, then
the falling edge of the CLK resets the Flip-Flop.
The output of the Error Amplifier integrates the
voltage difference between the feedback and
the 0.81V bandgap reference. The polarity is
such that a FB pin voltage lower than 0.81V
increases the EA output voltage. Since the EA
output voltage is proportional to the peak
inductor current, an increase in its voltage also
increases current delivered
the output.
to
x20
CURRENT SENSE
AMPLIFIER
--
+
D
REGULATOR
S
R
R
+
--
CURRENT
LIMIT
COMPARATOR
Q
DRIVER
M1
1
BST
6
SW
+
--
PWM
COMPARATOR
Figure 1—Functional Block Diagram
MP2359 Rev. 1.1
6/23/2006
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www.MonolithicPower.com
© 2006 MPS. All Rights Reserved.
5
TM
MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6
APPLICATION INFORMATION
Setting Output Voltage
The external resistor divider is used to set the
output voltage (see the schematic on front
page). Table 1 shows a list of resistor selection
for common output voltages. The feedback
resistor R1 also sets
loop
internal compensation
bandwidth with
capacitor (see Figure 1). R2 can be determined
by:
feedback
the
the
2R
=
1R
V
OUT −
V81.0
1
Table 1—Resistor Selection for Common
Output Voltages
VOUT (V)
1.8
2.5
3.3
5
R1 (kΩ)
80.6 (1%)
49.9 (1%)
49.9 (1%)
49.9 (1%)
R2 (kΩ)
64.9 (1%)
23.7 (1%)
16.2 (1%)
9.53 (1%)
than
least 25% percent higher
Selecting the Inductor
A 1µH to 10µH inductor with a DC current rating
of at
the
maximum load current is recommended for
most applications. For highest efficiency, the
inductor’s DC resistance should be less than
200mΩ. Refer to Table 2 for suggested surface
mount inductors. For most designs, the required
inductance value can be derived from the
following equation.
V
)
L
=
OUT
V
IN
V(
−
×
IN
I
×∆×
L
V
f
SW
OUT
Where ∆IL is the inductor ripple current.
Choose the inductor ripple current to be 30% of
the maximum
load current. The maximum
inductor peak current is calculated from:
I
(L
)MAX
=
I
LOAD
+
I
∆
L
2
Under light load conditions below 100mA, a
larger inductance is recommended for improved
efficiency. See Table 2 for suggested inductors.
Also note that the maximum recommended load
current is 1A if the duty cycle exceeds 35%.
their
from
the device. The
low ESR and small
Selecting the Input Capacitor
The input capacitor reduces the surge current
drawn from the input supply and the switching
noise
input capacitor
impedance at the switching frequency should be
less than the input source impedance to prevent
high frequency switching current from passing
through the input. Ceramic capacitors with X5R or
X7R dielectrics are highly recommended because
of
temperature
coefficients. For most applications, a 4.7µF
capacitor is sufficient.
Selecting the Output Capacitor
The output capacitor keeps the output voltage
ripple small and ensures feedback loop stability.
The output capacitor impedance should be low
at the switching frequency. Ceramic capacitors
with X5R or X7R dielectrics are recommended
for their low ESR characteristics. For most
applications, a 22µF ceramic capacitor will be
sufficient.
PC Board Layout
The high current paths (GND, IN and SW) should
be placed very close to the device with short,
direct and wide traces. The input capacitor needs
to be as close as possible to the IN and GND
pins. The external feedback resistors should be
placed next to the FB pin. Keep the switch node
traces short and away from the feedback network.
External Bootstrap Diode
It is recommended that an external bootstrap
diode be added when the input voltage is no
greater than 5V or the 5V rail is available in the
system. This helps improve the efficiency of the
regulator. The bootstrap diode can be a low
cost one such as IN4148 or BAT54.
5V (External) or
VIN (4.5V to 5V)
BS
MP2359
SW
10nF
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty cycle
operation (when
>65%) applications.
V
OUT
V
IN
MP2359 Rev. 1.1
6/23/2006
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
www.MonolithicPower.com
© 2006 MPS. All Rights Reserved.
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TM
MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6
Table 2—Suggested Surface Mount Inductors
Manufacturer
Toko
Sumida
Wurth Electronics
Part Number
A921CY-4R7M
CDRH4D28C/LD
7440530047
Inductance(µH) Max DCR(Ω)
4.7
4.7
4.7
0.027
0.036
0.038
TYPICAL APPLICATION CIRCUITS
Current
Rating (A)
1.66
1.5
2.0
Dimensions
L x W x H (mm3)
6 x 6.3 x 3
5.1 x 5.1 x 3
5.8 x 5.8 x 2.8
VIN
OFF ON
D3
1N4148
(Optional)
5
4
IN
BS
EN
MP2359
SW
Notes:
1) D3 can be installed if VIN < 5V
2) D2 can be installed if VOUT < 5V
3) No need for both D2 and D3
GND
FB
U1
1
6
3
D2
1N4148
(Optional)
C3
22nF
D1
B230A-13-F
Figure 3—1.4MHz, 3.3V Output at 1A Step-Down Converter
VIN
6V-12V
OFF ON
MP2359 Rev. 1.1
6/23/2006
1
6
3
5
IN
BST
MP2359 SW
4
EN
FB
GND
2
-VOUT
C3
10nF
D1
1N5819HW-7
-VOUT
-VOUT
-VOUT
Figure 4—White LED Driver Application
LED1
LED2
LED3
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© 2006 MPS. All Rights Reserved.
VOUT
3.3V
7
TM
MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6
PACKAGE INFORMATION
2.80
3.00
6
4
TSOT23-6
0.60
TYP
1.20
TYP
0.95
BSC
See Note 7
EXAMPLE
TOP MARK
PIN 1
AAAA
1.50
1.70
2.60
3.00
1
3
TOP VIEW
RECOMMENDED LAND PATTERN
0.84
0.90
1.00 MAX
SEATING PLANE
0.30
0.50
0.95 BSC
0.00
0.10
FRONT VIEW
SEE DETAIL "A"
SIDE VIEW
2.60
TYP
0.09
0.20
GAUGE PLANE
0.25 BSC
0o-8o
0.30
0.50
DETAIL “A”
NOTE:
1) ALL DIMENSIONS ARE IN MILLIMETERS.
2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,
PROTRUSION OR GATE BURR.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH
OR PROTRUSION.
4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING)
SHALL BE 0.10 MILLIMETERS MAX.
5) DRAWING CONFORMS TO JEDEC MO-193, VARIATION AB.
6) DRAWING IS NOT TO SCALE.
7) PIN 1 IS LOWER LEFT PIN WHEN READING TOP MARK FROM
LEFT TO RIGHT, (SEE EXAMPLE TOP MARK)
MP2359 Rev. 1.1
6/23/2006
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
www.MonolithicPower.com
© 2006 MPS. All Rights Reserved.
8