MP3418
400mA, 1.2MHz, Synchronous, Step-up
Converter with Output Disconnect
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP3418 is a high-efficiency, synchronous,
current–mode, step-up converter with output
disconnect.
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The MP3418 can start up from an input voltage
as low as 0.8V to provide inrush current limiting,
and output short-circuit protection. The
integrated, P-channel, synchronous rectifier
improves efficiency and eliminates the need for
an external Schottky diode. The PMOS
disconnects the output from the input when the
part shuts down. This output disconnect feature
allows the output to be completely discharged,
thus allowing the part to draw less than 1µA in
shutdown mode.
The 1.2MHz switching frequency allows for
smaller external components, while the internal
compensation and the soft-start minimize the
external component count: these feature help to
produce a compact solution for a wide current
load range.
The MP3418 is available in a small 8-pin
TSOT23 package.
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Up to 96% Efficiency
0.8V Low Voltage Start-Up
0.6V-to-4V Input Range
1.8V-to-4V Output Range
Internal Synchronous Rectifier
1.2MHz Fixed-Frequency Switching
Typical 38µA Quiescent Current
Typical 0.1µA Shutdown Current
Current-Mode Control with Internal
Compensation
True Output Disconnect from Input
VIN>VOUT Down Mode Operation
High Efficiency under Light-Load Conditions
Very Small External Components
Inrush Current Limiting and Internal SoftStart
Over-Voltage Protection
Short-Circuit Protection
TSOT23-8 Package
APPLICATIONS
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Battery-Powered Products
Personal Medical Devices
Portable Media Players
Wireless Peripherals
Handheld Computers and Smartphones
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 CIRCUIT
MP3418 Rev 1.0
2/7/2013
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1
MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
ORDERING INFORMATION
Part Number*
MP3418GJ
Package
TSOT23-8
Top Marking
AET
* For Tape & Reel, add suffix –Z (e.g. MP3418GJ–Z);
PACKAGE REFERENCE
TOP VIEW
IN
1
8
EN
OUT
2
7
FB
SW
3
6
AGND
PGND
4
5
NC
TSOT23-8
ABSOLUTE MAXIMUM RATINGS (1)
Thermal Resistance
SW Pin, OUT Pin ....................... -0.5V to +6.5V
All other Pins ................................. -0.5V to +6V
Continuous Power Dissipation (TA = 25°C) (2)
................................................................1.25W
Junction Temperature .............................. 150°C
Lead Temperature ................................... 260°C
Storage Temperature .............. –65°C to +150°C
TSOT23-8 ............................. 100 ..... 55 ... °C/W
Recommended Operating Conditions
(3)
Start-up Voltage VST.......................... 0.8V to 4V
Supply Voltage VIN ............................ 0.6V to 4V
VOUT .................................................. 1.8V to 4V
Operating Junction Temp. (TJ). -40°C to +125°C
MP3418 Rev 1.0
2/7/2013
(4)
θJA
θJC
Notes:
1) Exceeding these ratings may damage the device.
2) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ(MAX), the junction-toambient thermal resistance θJA, and the ambient temperature
TA. The maximum allowable continuous power dissipation at
any ambient temperature is calculated by PD(MAX)=(TJ(MAX)TA)/ θJA. Exceeding the maximum allowable power dissipation
will cause excessive die temperature, and the regulator will go
into thermal shutdown. Internal thermal shutdown circuitry
protects the device from permanent damage.
3) The device is not guaranteed to function outside of its
operation conditions.
4) Measured on JESD51-7 4-layer board.
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MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
ELECTRICAL CHARACTERISTICS
VIN = VEN = 1.8V, VOUT = 3.3V, TA = 25°C, unless otherwise noted.
Parameters
Symbol
Minimum Startup Voltage
Operating Input Voltage
Output Voltage Adjust Range
VST
VIN
VOUT
Quiescent Current
IQNS
Shutdown Current
IN Under-Voltage Lockout
Operation Frequency
Feedback Voltage
Feedback Input Current
NMOS On-Resistance
NMOS Leakage Current
ISD
VUVLO
fSW
VFB
IFB
RNDS_ON
IN_LK
PMOS On-Resistance
PMOS Leakage Current
Maximum Duty Cycle
Startup Current Limit
NMOS Current Limit
EN Input High Level
RPDS_ON
IP_LK
DMAX
IST_LIMIT
ISW_LIMIT
VEN_H
EN Input Low Level
EN Input Current
Thermal Shutdown(5)
Over Temperature Hysteresis(5)
VEN_L
IEN
Condition
Min
Typ
Max
Units
0.8
1.0
4
4.0
V
V
V
38
50
µA
0.1
0.5
1.2
1.21
1
110
0.1
1
0.6
1.4
1.23
50
µA
V
MHz
V
nA
mΩ
µA
0.6
1.8
VEN=VIN=1.8V, VOUT=3.3V, no load,
Measured on OUT pin
VEN=VOUT=0V, Measured on IN pin
VIN Rising
0.4
1.0
1.19
VFB=1.25V
VSW =6.5V
VSW =6.5V, VOUT=0V
85
300
0.7
Connect to VIN
0.6
120
0.1
90
200
400
1.2
150
20
1
1
500
0.1
2
mΩ
µA
%
mA
mA
V
V
uA
°C
°C
Notes:
5)Guaranteed by design, not tested
MP3418 Rev 1.0
2/7/2013
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MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
TYPICAL PERFORMANCE CHARACTERISTICS
Performance waveforms are tested on the evaluation board in the Design Example section.
VIN = 2.4V, VOUT = 3.3V, L = 6.8µH, COUT=10uF, TA = 25°C, unless otherwise noted.
MP3418 Rev 1.0
2/7/2013
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MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Performance waveforms are tested on the evaluation board in the Design Example section.
VIN = 2.4V, VOUT = 3.3V, L = 6.8µH, COUT=10uF, TA = 25°C, unless otherwise noted.
MP3418 Rev 1.0
2/7/2013
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MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Performance waveforms are tested on the evaluation board in the Design Example section.
VIN = 2.4V, VOUT = 3.3V, L = 6.8µH, COUT=10uF, TA = 25°C, unless otherwise noted.
MP3418 Rev 1.0
2/7/2013
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MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
PIN FUNCTIONS
Pin #
Name
1
IN
2
OUT
3
4
SW
PGND
5
NC
No Connection.
6
AGND
Analog Ground.
7
FB
Feedback. Connect to the tap of an external resistive voltage divider from the output to
FB to set the output voltage.
8
EN
Enable input. Turns regulator on (VEN>0.7V) or off (VEN<0.1V). Don’t apply a voltage
greater than 6.5V to this pin.
MP3418 Rev 1.0
2/7/2013
Pin Function
Input Supply. Requires bypass capacitor.
Output Node. Source of the internal synchronous rectifier. Place the output capacitor as
close as possible between OUT and PGND.
Output Switch Node. Connect the inductor to SW to complete the step-up converter.
Power Ground. Reference ground of the regulated output voltage.
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MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
BLOCK DIAGRAM
V IN
Cin
L
PGND
SW
IN
OFF ON
EN
Bias and
Voltage Ref
Enable
V IN
V BETTER
Body
Control
OVP
VOUT
OUT
VDD
HS
+
-
Thermal
Control
FB
Startup
Mode Control
Cout
Zero current
Cross COMP
Driver and
Controllogic
R1
PGND
LS
PGND
Oscillator
Slope
COMP
Current Sense
Amplifier
+
-
S
PGND
FB
+
-
-
EA
AGND
Clamp
+
+
PWM
C OMP
Soft Start
OUT
R2
1. 21V
PGND
Figure 1: Functional Block Diagram
MP3418 Rev 1.0
2/7/2013
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MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
OPERATION
The MP3418 is a 1.2MHz, synchronous, stepup converter housed in a compact TSOT23
package with true output disconnect. Able to
operate at low-input voltages of less than 0.8V,
the device features fixed-frequency currentmode PWM control for exceptional line and load
regulation. Internal soft-start and loop
compensation simplify the design process and
minimize the external components. The internal
low-RDS(ON) MOSFETs combined with Power
Save Mode operation enable the device to
maintain high efficiency over a wide currentload range.
Synchronous Rectifier
The MP3418 integrates an N-channel and a Pchannel MOSFET to realize a synchronous
rectifier. Replacing the traditional Schottky
diode with a low-RDS(ON) PMOS improves
efficiency. In a conventional synchronous
rectifier, the PMOS body diode is forwardbiased, and the current flows from VIN to VOUT.
The MP3418 allows for true output disconnect
by eliminating the body diode, and prevents
battery depletion when the converter shuts
down. To prevent excessive inductor current,
the PMOS synchronous rectifier only functions
when VOUT > (VIN +200mV).
Start-Up
When EN is on, the MP3418 starts up with a
linear charge period. During this linear charge
period, the rectifier PMOS turns on until the
output capacitor charges to VIN–200mV; the
PMOS current is limited during this period to
around 200mA to avoid inrush current. This
circuit also helps to limit the output current
under short circuit conditions.
After the linear charging period, the device
starts switching. If VOUT remains below 1.7V, the
part then works in free-running mode; in this
mode, the device works in open loop first at a
variable frequency then at a fixed 500kHz
switching frequency, the duty cycle depends on
the input-output ratio, and the switching current
is limited to 400mA to avoid the start-up current
inrush.
The internal soft-start (SS) does not take
charge and continues to rise following the FB
voltage during the linear charging and freeMP3418 Rev 1.0
2/7/2013
running period. Once the output voltage
reaches 1.7V, the normal closed-loop operation
initiates, VOUT starts to rise under the control of
SS. It then works either in boost mode or down
mode depending on VIN and VOUT. Table 1 lists
the operation modes during start up.
Table 1: Operation Mode during Start-Up
Sequence
VOUT <Vin-200mV & VOUT <1.7V
Linear Charge
VOUT ≥Vin-200mV & VOUT <1.7V
Free Running
VOUT <Vin+200mV & VOUT ≥1.7V
Down mode
VOUT >Vin+200mV & VOUT ≥1.7V
Boost Mode
In normal mode, when VOUT>VIN+200mV, the
MP3418 powers itself from VOUT instead of VIN.
This allows the battery voltage to drop to as low
as 0.6V without affecting the circuit operation.
The battery supplies sufficient energy to the
output and becomes the only limiting factor in
the application.
Device Enable
The device operates when EN is high (>0.7V). It
enters shutdown mode when EN is set to low
(<0.1V). In shutdown mode, the regulator stops
switching and halts all internal control circuitry
and eliminate body-diode conduction of the
internal PMOS rectifier. This isolates the load
from the input, and means that the output
voltage can drop below the input voltage during
shutdown.
Power-Save Mode
The MP3418 automatically enters power-save
mode (PSM) when the load decreases, and
resumes PWM mode when the load increases.
In PSM, the converter only operates when the
output voltage falls below the set threshold, and
ramps up by several pulses with the same
switching frequency as PWM mode. It resumes
power-save mode once the output voltage
exceeds the high threshold. PSM requires
fewer circuit resources than PWM mode. All
unused circuitry is disabled, so as to reduce
quiescent power dissipation as well as
switching power loss. The OUT pin voltage-
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9
MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
monitoring circuit and error amplifier with loop
compensation for peak-current– mode control
remain active.
The output ripple, which is usually around 1%
peak to peak, can be reduced by increasing the
output capacitance and also by adding a small
feed-forward capacitance (around 5.6pF).
The MP3418 operates from PSM to PWM mode
depending on the load, which varies with the
input voltage, inductor value, and the output
capacitor value.
Under-Voltage Lockout
Under-voltage lockout prevents device startup
when VIN falls below 0.5V while in operation and
the battery is being discharged.
Error Amplifier
The error amplifier (EA) is an internallycompensated amplifier. The EA compares the
internal 1.21V reference voltage against VFB to
generate an error signal. The output voltage of
MP3418 could be adjusted from 1.8V to 4V by
connecting FB to the tap of an external voltage
divider from VOUT to ground, as per the following
equation:
R1
VOUT = 1.21V × (1 + R2
)
(1)
Set R1 and R2 as large as possible to achieve
a low quiescent current. Usually, select an R1
value larger than 300k for good stability and
transient balance.
Current Sensing
Lossless current sensing converts the NMOS
switch current signal to a voltage that can be
summed with the internal slope compensator.
The difference between this summed signal and
the error amplifier output provides control over
the peak current through the PWM. Peak switch
current is limited to approximately 400mA,
independent of input or output voltage. The
switching current signal is blanked for 60ns to
enhance noise rejection.
Thermal Protection
The device has an internal temperature monitor
If the die temperature exceeds 150°C, the
switches turn off. Once the output drops below
1.7V, it will turn on..
MP3418 Rev 1.0
2/7/2013
Output Disconnect and Inrush Limiting
The MP3418 is designed to allow true output
disconnect by eliminating the internal PMOS
rectifier’s body diode conduction. This feature
allows VOUT to go to 0V during shutdown and
draw 0A from the input source. It also allows for
inrush current limiting at start-up, which
minimizes surge currents at the input supply.
Note that to optimize output disconnect,
exclude the external Schottky diode between
SW and VOUT.
To minimize voltage overshoot on the SW pin
due to stray inductance, keep the output filter
capacitor as close as possible to the VOUT pin
and use very low ESR/ESL ceramic capacitors
tied to a clean ground plane.
Short-Circuit Protection
Unlike most step-up converters, the MP3418
allows for short circuits on the output. In the
event of a short circuit, the device first turns off
the NMOS when the sensed current reaches
the current limit. The device then enters a linear
charge period with the current limited as with
the start-up period. In addition, the thermal
regulation circuit further controls the input
current if the die temperature rises above
150°C.
Down Mode (VIN>VOUT) Operation
The MP3418 will continue to regulate the output
voltage even when the input voltage exceeds
the output voltage. This is achieved by
terminating the switching at the synchronous
PMOS and applying VIN statically on its gate.
This ensures that the slope of the inductor
current will reverse while current flows to the
output. Since the PMOS no longer acts as a
low-impedance switch in this mode, power
dissipation increases within the IC to cause a
sharp drop in efficiency. Limit the maximum
output current to maintain an acceptable
junction temperature.
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10
MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
APPLICATION INFORMATION
COMPONENT SELECTION
Input Capacitor Selection
Low ESR input capacitors reduce input
switching noise and reduce the peak current
drawn from the battery. It follows that ceramic
capacitors are also a good choice for input
decoupling and should be located as close as
possible to the device. Add a ceramic capacitor
larger than 4.7µF in parallel with a 100nF
ceramic capacitor close to the IC.
Output Capacitor Selection
The output capacitor requires a minimum
capacitance value of 10µF at the programmed
output voltage to ensure stability over the full
operating range. A higher capacitance value
may be required to lower the output ripple and
also the transient response. Low ESR
capacitors, such as X5R- or X7R-type ceramic
capacitors, are recommended. Assuming that
the ESR is zero, estimate the minimum output
capacitance to support the ripple in the PWM
mode as.
CO ≥
IO × (VOUT(MAX) − VIN(MIN) )
fS × V OUT(MAX) ×∆V
(2)
Where,
VOUT(MAX) = Maximum output voltage
VIN(MIN) = Minimum Input voltage
IO=Output current
fS = Switching frequency
∆V= Acceptable output ripple
Additional output capacitance may also be
required for applications where VIN≈VOUT to
reduce ripple in PSM mode and to ensure
stability in PWM mode, especially at higher
output load currents.
Inductor Selection
The MP3418 can use small surface-mount
inductors due to its 1.2MHz switching frequency.
Inductor values between 4.7µH and 10µH are
suitable for most applications. Larger values of
inductance will allow slightly greater output
current capability (and lower the PSM threshold)
by reducing the inductor ripple current.
Increasing the inductance above 10µH will
MP3418 Rev 1.0
2/7/2013
increase component size while providing little
improvement in output current capability. The
minimum inductance value is given by:
VIN(MIN) × (VOUT(MAX) − VIN(MIN) )
L≥
(3)
2 × V OUT(MAX) ×∆IL × fS
Where ∆IL is the acceptable inductor current
ripple
The inductor current ripple is typically set at
30% to 40% of the maximum inductor current.
High-frequency ferrite-core inductor materials
reduce frequency-dependent power losses and
improve efficiency compared to cheaper
powdered-iron cores. The inductor should have
low DCR (inductor series resistance without
saturated windings) to reduce the resistive
power loss; further reducing the DCR will
significantly
improve
efficiency
when
DCR<<RDS-ON. Select a large-enough saturation
current (ISAT) to support the current peak.
The device enters PSM at a load that borders
continuous and discontinuous PWM operation,
which means the averaged inductor current
(IAVG) is equal to half of the inductor current
ripple (∆IL). So a larger inductor may lead to a
lower PSM enter level.
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11
MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
PCB Layout Considerations
Layout is important, especially for switching
power supplies with high switching frequencies;
poor layout results in reduced performance,
EMI problems, resistive loss, and even system
instability.
Following the rules below can help ensure a
stable layout design:
1. Place a decoupling capacitor (>100nF) as
close as possible from VOUT to PGND. Avoid
placing vias between the OUT pin and the
output capacitor to reduce spikes on the SW
node and improve EMI performance.
GND
2. Place the input capacitor, output capacitor,
and inductor as close to the IC as possible
with a short and wide trace.
3. Place the feedback divider resistors as
close as possible to the control GND
(AGND) pin.
4. Use a large copper GND area to lower the
die temperature.
Figure 2 shows the recommended component
placement for the MP3418.
Vin
Top Layer
Bottom Layer
Via
Via
IN
OUT
EN
MP 3418
SW
PGND
Put this Decoupling Cap
close to OUT and GND
FB
AGND
NC
Vout
Figure 2: Recommended PCB Layout
MP3418 Rev 1.0
2/7/2013
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MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
TYPICAL APPLICATION CIRCUITS
L
6.8 µH
3
SW
V IN
1.2V
1
C1A
C1B
4.7µF 0.1µF
OUT
2
MP3418
5
8
R3 100k
IN
R1
365k
NC
EN
P GND
4
FB
A GND
6
C2A
0.1µF
C2B
10 µ F
VOUT
1.8V
7
R2
750k
Figure 3: Boost Circuit. VIN=1.2V, VOUT=1.8V.
MP3418 Rev 1.0
2/7/2013
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MP3418 – 400mA, 1.2MHz, SYNCHRONOUS, STEP-UP CONVERTER WITH OUTPUT DISCONNECT
PACKAGE INFORMATION
TSOT23-8
RECOMMENDED LAND PATTERN
TOP VIEW
SEATING PLANE
SEE DETAIL ''A ''
FRONT VIEW
SIDE VIEW
NOTE:
DETAIL ''A''
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) JEDEC REFERENCE IS MO-193, 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.
MP3418 Rev. 1.0
2/7/2013
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14