TM

MP2359
1.2A, 24V, 1.4MHz
Step-Down Converter in a TSOT23-6
The Future of Analog IC Technology TM

DESCRIPTION FEATURES
The MP2359 is a monolithic step-down switch • 1.2A Peak Output Current
mode converter with a built-in power MOSFET. • 0.35Ω Internal Power MOSFET Switch
It achieves 1.2A peak output current over a • Stable with Low ESR Output Ceramic
wide input supply range with excellent load and Capacitors
line regulation. Current mode operation • Up to 92% Efficiency
provides fast transient response and eases loop • 0.1µA Shutdown Mode
stabilization. Fault condition protection includes • Fixed 1.4MHz Frequency
cycle-by-cycle current limiting and thermal • Thermal Shutdown
shutdown.
• Cycle-by-Cycle Over Current Protection
The MP2359 requires a minimum number of • Wide 4.5V to 24V Operating Input Range
readily available standard external components. • Output Adjustable from 0.81V to 15V
The MP2359 is available in TSOT23-6 and • Available in TSOT23-6 and SOT23-6
SOT23-6 packages. Packages
EVALUATION BOARD REFERENCE APPLICATIONS
Board Number Dimensions • Distributed Power Systems
EV2359DJ-00B 2.1”X x 1.9”Y x 0.4”Z • 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
Efficiency vs
Load Currents
5 1
100
VIN IN BST VIN = 12V
90
12V CB
10nF 80
6 VOUT 70
EFFICIENCY (%)

SW VIN = 24V
MP2359 D1
3.3V @ 1.2A
60
B230A 50
4 3 40
OFF ON EN FB
GND 30
2 20
10 VOUT = 5V
0
0.01 0.1 1 10
LOAD CURRENT (A)

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MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6

PACKAGE REFERENCE ABSOLUTE MAXIMUM RATINGS (1)

Supply Voltage VIN ....................................... 26V
VSW....................................... –0.3V to VIN + 0.3V
VBS ....................................................... VSW + 6V
TOP VIEW All Other Pins................................. –0.3V to +6V
Junction Temperature...............................150°C
BST 1 6 SW
Lead Temperature ....................................260°C
Storage Temperature ..............–65°C to +150°C
GND 2 5 IN
(2)
Recommended Operating Conditions
FB 3 4 EN Supply Voltage VIN ........................... 4.5V to 24V
Output Voltage VOUT ...................... 0.81V to 15V
Ambient Temperature ................–40°C to +85°C
(3)
Thermal Resistance θJA θJC
Part Number* Package Temperature TSOT23-6.............................. 220 .... 110.. °C/W
SOT23-6 ................................ 220 .... 110.. °C/W
MP2359DJ TSOT23-6 –40°C to +85°C
MP2359DT SOT23-6 –40°C to +85°C Notes:
1) Exceeding these ratings may damage the device.
* For Tape & Reel, add suffix –Z (eg. MP2359DJ–Z) 2) The device function is not guaranteed outside of the
For RoHS compliant packaging, add suffix –LF (eg. recommended operating conditions.
MP2359DJ–LF–Z) 3) Measured on approximately 1” square of 1 oz copper.

ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameters Symbol Condition Min Typ Max Units
Feedback Voltage VFB 4.5V ≤ VIN ≤ 24V 0.790 0.810 0.830 V
Feedback Current IFB VFB = 0.8V 0.1 µA
Switch-On Resistance (4) RDS(ON) 0.35 Ω
Switch Leakage VEN = 0V, VSW = 0V 10 µA
Current Limit (4) 1.8 A
Oscillator Frequency fSW VFB = 0.6V 1.2 1.4 1.7 MHz
Fold-back Frequency VFB = 0V 460 KHz
Maximum Duty Cycle VFB = 0.6V 87 %
Minimum On-Time (4) tON 100 ns
Under Voltage Lockout Threshold Rising 2.5 2.8 3.1 V
Under Voltage Lockout Threshold Hysteresis 150 mV
EN Input Low Voltage 0.4 V
EN Input High Voltage 1.2 V
VEN = 2V 2.1
EN Input Current µA
VEN = 0V 0.1
Supply Current (Shutdown) IS VEN = 0V 0.1 1.0 µA
Supply Current (Quiescent) IQ VEN = 2V, VFB = 1V 0.8 1.0 mA
Thermal Shutdown (4) 150 °C
Note:
4) Guaranteed by design.

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MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6

PIN FUNCTIONS
Pin # Name Description
Bootstrap. A capacitor is connected between SW and BS pins to form a floating supply across
1 BST 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
2 GND 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
3 FB
frequency foldback comparator lowers the oscillator frequency when the FB voltage is below
250mV.
4 EN On/Off Control Input. Pull EN above 1.2V to turn the device on.
Supply Voltage. The MP2359 operates from a +4.5V to +24V unregulated input. C1 is needed
5 IN
to prevent large voltage spikes from appearing at the input.
6 SW Switch Output.

TYPICAL PERFORMANCE CHARACTERISTICS

VIN = 12V, VOUT = 3.3V, L = 4.7µH, C1 = 10µF, C2 = 22µF, TA = +25ºC, unless otherwise noted.
Efficiency vs Efficiency vs
Load Current Load Current
100 100
VIN = 12V
90 VIN = 18V 90
80 80
70
EFFICIENCY (%)

70
EFFICIENCY (%)

VIN = 24V
60 60
VIN = 24V
50 50
40 40
30 30
20 20
10 VOUT = 2.5V 10 VOUT = 5V
0 0
0.01 0.1 1 10 0.01 0.1 1 10
LOAD CURRENT ( A) LOAD CURRENT (A)

Feedback Voltage vs Switching Frequency vs

Die Temperature Die Temperature
0.820 1.50
SWITCHING FREQUENCY (MHz)

0.818 1.48
FEEDBACK VOLTAGE (V)

0.816 1.46
0.814 1.44
0.812 1.42
0.810 1.40
0.808 1.38
0.806 1.36
0.804 1.34
0.802 1.32
0.800 1.30
-50 -25 0 25 50 75 100 125 150 -50 -25 0 25 50 75 100 125 150
DIE TEMPERATURE (OC) DIE TEMPERATURE (OC)

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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.

Current Limit vs Steady State Test

Duty Cycle IOUT = 0.5A
3.0

2.5 VOUT
VOUT 20mV/div.
CURRENT LIMIT (A)

AC Coupled
2.0
50mV/div.

1.5 VSW
IL 10V/div.
1.0 1A/div.
IL
500mA/div.
0.5 ILOAD
1A/div.

0
0 20 40 60 80 100 400ns/div.
DUTY CYCLE (%)

Short Circuit Entry Short Circuit Recovery Start-up through Enable

No Load

VEN
5V/div.

VOUT VOUT
1V/div. 1V/div.
VOUT
1V/div.

VSW
IL 10V/div.
1A/div. IL IL
1A/div. 500mA/div.

Start-up through Enable Shut-down through Enable Shut-down through Enable

IOUT = 1A Resistive Load No Load IOUT = 1A Resistive Load

VEN VEN
VEN
5V/div. 5V/div.
VOUT 5V/div.
2V/div.

VOUT VOUT
1V/div. 2V/div.
VSW
VSW VSW
10V/div.
10V/div. 10V/div.

IL IL IL
1A/div. 1A/div. 1A/div.

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MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6

OPERATION
The MP2359 is a current mode buck regulator. If the sum of the Current Sense Amplifier output
That is, the EA output voltage is proportional to and the Slope Compensation signal does not
the peak inductor current. exceed the EA output for a whole cycle, then
the falling edge of the CLK resets the Flip-Flop.
At the beginning of a cycle, M1 is off. The EA
output voltage is higher than the current sense The output of the Error Amplifier integrates the
amplifier output, and the current comparator’s voltage difference between the feedback and
output is low. The rising edge of the 1.4MHz the 0.81V bandgap reference. The polarity is
CLK signal sets the RS Flip-Flop. Its output such that a FB pin voltage lower than 0.81V
turns on M1 thus connecting the SW pin and increases the EA output voltage. Since the EA
inductor to the input supply. output voltage is proportional to the peak
inductor current, an increase in its voltage also
The increasing inductor current is sensed and
increases current delivered to the output.
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
CURRENT SENSE
AMPLIFIER
x20 --
+

RAMP D
GENERATOR REGULATOR
1 BST

EN 4 REGULATOR OSCILLATOR
1.4MHz/460KHz S Q DRIVER M1
+
-- R
R 6 SW
1pF CURRENT
LIMIT
COMPARATOR
REFERENCE 27pF

+
+EA
--
FB 3 -- PWM
ERROR COMPARATOR
AMPLIFIER
GND 2

Figure 1—Functional Block Diagram

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MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6

APPLICATION INFORMATION
Setting Output Voltage Selecting the Input Capacitor
The external resistor divider is used to set the The input capacitor reduces the surge current
output voltage (see the schematic on front drawn from the input supply and the switching
page). Table 1 shows a list of resistor selection noise from the device. The input capacitor
for common output voltages. The feedback impedance at the switching frequency should be
resistor R1 also sets the feedback loop less than the input source impedance to prevent
bandwidth with the internal compensation high frequency switching current from passing
capacitor (see Figure 1). R2 can be determined through the input. Ceramic capacitors with X5R or
by: X7R dielectrics are highly recommended because
R1 of their low ESR and small temperature
R2 =
VOUT coefficients. For most applications, a 4.7µF
−1 capacitor is sufficient.
0.81V
Table 1—Resistor Selection for Common Selecting the Output Capacitor
Output Voltages The output capacitor keeps the output voltage
ripple small and ensures feedback loop stability.
VOUT (V) R1 (kΩ) R2 (kΩ) The output capacitor impedance should be low
1.8 80.6 (1%) 64.9 (1%) at the switching frequency. Ceramic capacitors
2.5 49.9 (1%) 23.7 (1%) with X5R or X7R dielectrics are recommended
for their low ESR characteristics. For most
3.3 49.9 (1%) 16.2 (1%)
applications, a 22µF ceramic capacitor will be
5 49.9 (1%) 9.53 (1%) sufficient.

Selecting the Inductor PC Board Layout

A 1µH to 10µH inductor with a DC current rating The high current paths (GND, IN and SW) should
of at least 25% percent higher than the be placed very close to the device with short,
maximum load current is recommended for direct and wide traces. The input capacitor needs
most applications. For highest efficiency, the to be as close as possible to the IN and GND
inductor’s DC resistance should be less than pins. The external feedback resistors should be
200mΩ. Refer to Table 2 for suggested surface placed next to the FB pin. Keep the switch node
mount inductors. For most designs, the required traces short and away from the feedback network.
inductance value can be derived from the External Bootstrap Diode
following equation. It is recommended that an external bootstrap
VOUT × ( VIN − VOUT ) diode be added when the input voltage is no
L= greater than 5V or the 5V rail is available in the
VIN × ∆IL × f SW
system. This helps improve the efficiency of the
Where ∆IL is the inductor ripple current. regulator. The bootstrap diode can be a low
cost one such as IN4148 or BAT54.
Choose the inductor ripple current to be 30% of
5V (External) or
the maximum load current. The maximum VIN (4.5V to 5V)
inductor peak current is calculated from:
∆I L BS
IL(MAX ) = ILOAD +
2 MP2359 10nF

Under light load conditions below 100mA, a SW

larger inductance is recommended for improved

efficiency. See Table 2 for suggested inductors. Figure 2—External Bootstrap Diode
Also note that the maximum recommended load This diode is also recommended for high duty cycle
current is 1A if the duty cycle exceeds 35%. VOUT
operation (when >65%) applications.
VIN

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MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6

Table 2—Suggested Surface Mount Inductors

Current Dimensions
Manufacturer Part Number Inductance(µH) Max DCR(Ω) L x W x H (mm3)
Rating (A)
Toko A921CY-4R7M 4.7 0.027 1.66 6 x 6.3 x 3
Sumida CDRH4D28C/LD 4.7 0.036 1.5 5.1 x 5.1 x 3
Wurth Electronics 7440530047 4.7 0.038 2.0 5.8 x 5.8 x 2.8

TYPICAL APPLICATION CIRCUITS

D3
1N4148
(Optional)
5 1
VIN IN BS

D2
C3 1N4148
22nF (Optional)
4 6 VOUT
OFF ON EN MP2359 SW
3.3V
D1
B230A-13-F
Notes:
1) D3 can be installed if VIN < 5V
2) D2 can be installed if VOUT < 5V 3
FB
3) No need for both D2 and D3 GND
U1

Figure 3—1.4MHz, 3.3V Output at 1A Step-Down Converter

5 1
VIN IN BST
6V-12V C3
10nF
6
SW
MP2359 D1
1N5819HW-7
LED1
-VOUT -VOUT
4 3
OFF ON EN FB LED2
GND
2
-VOUT LED3
-VOUT

Figure 4—White LED Driver Application

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MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6

PACKAGE INFORMATION
TSOT23-6
0.60 0.95
2.80 TYP BSC
3.00

6 4
1.20
TYP
See Note 7
EXAMPLE

AAAA
TOP MARK
1.50 2.60 2.60
1.70 3.00 TYP
PIN 1

1 3

TOP VIEW RECOMMENDED LAND PATTERN

0.84
0.90 1.00 MAX
0.09
SEATING PLANE 0.20
0.30 0.00
0.95 BSC
0.50 0.10 SEE DETAIL "A"

FRONT VIEW SIDE VIEW

NOTE:
1) ALL DIMENSIONS ARE IN MILLIMETERS.
GAUGE PLANE 2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,
0.25 BSC PROTRUSION OR GATE BURR.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH
OR PROTRUSION.
4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING)
0.30 SHALL BE 0.10 MILLIMETERS MAX.
0o-8o 0.50 5) DRAWING CONFORMS TO JEDEC MO-193, VARIATION AB.
6) DRAWING IS NOT TO SCALE.
DETAIL “A” 7) PIN 1 IS LOWER LEFT PIN WHEN READING TOP MARK FROM
LEFT TO RIGHT, (SEE EXAMPLE TOP MARK)

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MP2359 – 1.2A, 24V, 1.4MHz STEP-DOWN CONVERTER IN A TSOT23-6

SOT23-6
0.60 0.95
2.80 TYP BSC
3.00

6 4
1.20
TYP
See Note 7
EXAMPLE
TOP MARK

PIN 1
AAAA 1.50
1.70
2.60
3.00
2.60
TYP

1 3

TOP VIEW RECOMMENDED LAND PATTERN

0.90
1.30 1.45 MAX

0.09
SEATING PLANE 0.20
0.30 0.00 SEE DETAIL "A"
0.95 BSC
0.50 0.15

FRONT VIEW SIDE VIEW

NOTE:
1) ALL DIMENSIONS ARE IN MILLIMETERS.
GAUGE PLANE 2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,
0.25 BSC PROTRUSION OR GATE BURR.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH
OR PROTRUSION.
4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING)
0.30 SHALL BE 0.10 MILLIMETERS MAX.
0o-8o 0.55 5) DRAWING CONFORMS TO JEDEC MO-193, VARIATION AB.
6) DRAWING IS NOT TO SCALE.
DETAIL “A” 7) PIN 1 IS LOWER LEFT PIN WHEN READING TOP MARK FROM
LEFT TO RIGHT, (SEE EXAMPLE TOP MARK)

NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications.
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.

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