MP2235GJ-Z [MPS]
Switching Regulator, Current-mode, 6A, 800kHz Switching Freq-Max, PDSO8, MO-193BA, TSOT-23, 8 PIN;
| 型号： | MP2235GJ-Z |
| 厂家： | 
MONOLITHIC POWER SYSTEMS |
| 描述： | Switching Regulator, Current-mode, 6A, 800kHz Switching Freq-Max, PDSO8, MO-193BA, TSOT-23, 8 PIN 开关 光电二极管 输出元件 |
| 文件： | 总21页 (文件大小：1220K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MP2235
High-Efficiency, 3A, 16V, 800kHz
Synchronous, Step-Down Converter
DESCRIPTION
FEATURES
The MP2235 is a high-frequency, synchronous,
rectified, step-down, switch-mode converter
with built-in power MOSFETs. It offers a very
compact solution to achieve a 3A continuous
output current with excellent load and line
regulation over a wide input supply range. The
MP2235 has synchronous mode operation for
higher efficiency over the output current load
range.
Wide 4.5V-to-16V Operating Input Range
80mΩ/30mΩ Low RDS(ON) Internal Power
MOSFETs
High-Efficiency Synchronous Mode
Operation
Fixed 800kHz Switching Frequency
Synchronizes from a 300kHz-to-2MHz
External Clock
Power-Save Mode at Light Load
External Soft-Start
OCP Protection and Hiccup
Thermal Shutdown
Output Adjustable from 0.8V
Available in an 8-pin TSOT-23 Package
Current-mode operation provides fast transient
response and eases loop stabilization.
Full protection features include over-current
protection and thermal shut down.
The MP2235 requires a minimal number of
readily-available standard external components,
and is available in a space-saving 8-pin
TSOT23 package.
APPLICATIONS
Notebook Systems and I/O Power
Digital Set-Top Boxes
Flat-Panel Television and Monitors
Distributed Power Systems
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
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
1
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
ORDERING INFORMATION
Part Number*
Package
Top Marking
MP2235GJ
TSOT-23-8
AFL
* For Tape & Reel, add suffix –Z (e.g. MP2235GJ–Z);
PACKAGE REFERENCE
ABSOLUTE MAXIMUM RATINGS (1)
Thermal Resistance (5)
TSOT-23-8............................ 100..... 55... °C/W
θJA θJC
VIN ................................................ -0.3V to 17V
VSW ....................................................................
-0.3V (-5V for <10ns) to 17V (19V for <10ns)
VBST ...................................................... VSW+6V
All Other Pins................................-0.3V to 6V (2)
Notes:
1) Exceeding these ratings may damage the device.
2) About the details of EN pin’s ABS MAX rating, please refer to
Page 9, Enable/SYNC control section.
3) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ (MAX), the junction-to-
ambient 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)
Continuous Power Dissipation (TA = +25°C)
..........................................................1.25W
Junction Temperature..............................150°C
Lead Temperature ...................................260°C
Storage Temperature.................-65°C to 150°C
Recommended Operating Conditions (4)
Supply Voltage VIN .......................... 4.5V to 16V
Output Voltage VOUT................0.8V to VIN x 90%
Operating Junction Temp. (TJ). -40°C to +125°C
4) The device is not guaranteed to function outside of its
operating conditions.
5) Measured on JESD51-7, 4-layer PCB.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
2
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS (6)
VIN = 12V, TA = 25°C, unless otherwise noted.
Parameter
Symbol Condition
Min
Typ
Max
1
Units
μA
Supply Current (Shutdown)
Supply Current (Quiescent)
HS Switch-On Resistance
LS Switch-On Resistance
Switch Leakage
IIN
Iq
VEN = 0V
VEN = 2V, VFB = 1V
0.6
80
30
0.8
mA
mΩ
mΩ
μA
HSRDS-ON VBST-SW=5V
LSRDS-ON VCC =5V
SWLKG
ILIMIT
fSW
VEN = 0V, VSW =12V
0.3
6
Current Limit
Under 40% Duty Cycle
VFB=0.75V
4
5
A
Oscillator Frequency
Fold-Back Frequency
Maximum Duty Cycle
Minimum On Time(6)
Sync Frequency Range
690
800
0.25
95
870
kHz
fSW
fFB
VFB<400mV
DMAX
τON_MIN
fSYNC
VFB=700mV
90
%
40
ns
0.3
2
MHz
Feedback Voltage
VFB
TA =25°C
791
807
823
mV
Feedback Current
EN Rising Threshold
EN Hysteresis
IFB
VFB=820mV
10
1.4
175
50
1.6
240
nA
V
VEN_RISING
VEN_Hysteresis
1.2
110
mV
VEN=2V
VEN=0
2
μA
EN Input Current
EN Turn-Off Delay
IEN
0
5
μA
ENtd-off
3
7
μs
VIN Under-Voltage Lockout
Threshold—Rising
INUVVth
3.7
3.9
4.1
V
VIN Under-Voltage Lockout
Threshold—Hysteresis
INUVHYS
VCC
530
4.6
610
690
mV
VCC Regulator
4.9
1.5
11
5.2
3
V
VCC Load Regulation
Soft-Start Current
Thermal Shutdown (6)
Thermal Hysteresis (6)
ICC=5mA
%
ISS
8
14
μA
°C
°C
150
20
Notes:
6) Guaranteed by design.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
3
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL CHARACTERISTICS
VIN = 12V, VOUT = 3.3V, L=3.3μH, TA = 25°C, unless otherwise noted.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
4
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 12V, VOUT = 3.3V, L=4.7μH, TA = 25°C, unless otherwise noted.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
5
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 12V, VOUT = 3.3V, L=3.3μH, TA = 25°C, unless otherwise noted.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
6
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 12V, VOUT = 3.3V, L=3.3μH, TA = 25°C, unless otherwise noted.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
7
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
PIN FUNCTIONS
Package
Pin #
Name Description
Soft-Start. Connect an external capacitor to program the soft start time for the switch mode
regulator.
1
SS
IN
Supply Voltage. The IN pin supplies power for internal MOSFET and regulator. The
MP2235 operates from a +4.5V to +16V input rail. Requires a low-ESR, and low-
inductance capacitor (C1) to decouple the input rail. Place the input capacitor very close to
this pin and connect it with wide PCB traces and multiple vias.
2
3
Switch Output. Connect to the inductor and bootstrap capacitor. This pin is driven up to VIN
by the high-side switch during the PWM duty cycle ON time. The inductor current drives
the SW pin negative during the OFF time. The ON resistance of the low-side switch and
the internal body diode fixes the negative voltage. Connect using wide PCB traces and
multiple vias.
SW
System Ground. Reference ground of the regulated output voltage. PCB layout Requires
extra care. For best results, connect to GND with copper and vias.
4
5
6
7
GND
BST
Bootstrap. Requires a capacitor connected between SW and BST pins to form a floating
supply across the high-side switch driver.
Enable. EN=high to enable the MP2235. Apply an external clock change the switching
frequency. For automatic start-up, connect EN pin to VIN with a 100kΩ resistor.
EN/SYNC
VCC
Internal 5V LDO output. Powers the driver and control circuits. Decouple with 0.1μF-to-
0.22μF capacitor. Do not use a capacitor ≥0.22μF.
Feedback. Connect to the tap of an external resistor divider from the output to GND to set
the output voltage. The frequency fold-back comparator lowers the oscillator frequency
when the FB voltage is below 400mV to prevent current limit runaway during a short circuit
fault. Place the resistor divider as close to the FB pin as possible. Avoid placing vias on
the FB traces.
8
FB
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
8
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
FUNCTIONAL BLOCK DIAGRAM
Figure 1: Functional Block Diagram
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
9
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
OPERATION
The MP2235 is a high-frequency, synchronous,
rectified, step-down, switch-mode converter
with built-in power MOSFETs. It offers a very
compact solution that achieves a 3A continuous
output current with excellent load and line
regulation over a wide input supply range.
The EN pin is clamped internally using a 6.5V
series-Zener-diode as shown in Figure 2.
Connecting the EN input pin through a pullup
resistor to the voltage on the IN pin limits the
EN input current to less than 100µA.
For example, with 12V connected to IN, RPULLUP
≥ (12V – 6.5V) ÷ 100µA = 55kΩ.
The MP2235 operates in a fixed-frequency,
peak-current–control mode to regulate the
output voltage. An internal clock initiates a
PWM cycle. The integrated high-side power
MOSFET turns on and remains on until the
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,
within 95% of one PWM period, the current in
the power MOSFET does not reach the value
set by the COMP value, the power MOSFET is
forced off.
Connecting the EN pin is directly to a voltage
source without any pullup resistor requires
limiting the amplitude of the voltage source to
≤6V to prevent damage to the Zener diode.
Figure 2: 6.5V Zener Diode Connection
Internal Regulator
For external clock synchronization, connect a
clock with a frequency range between 300kHz
and 2MHz 2ms after the output voltage is set:
The internal clock rising edge will synchronize
with the external clock rising edge. Select an
external clock signal with a pulse width less
than 1.2μs.
A 5V internal regulator powers most of the
internal circuitries. This regulator takes VIN and
operates in the full VIN range. When VIN
exceeds 5.0V, the output of the regulator is in
full regulation. When VIN is less than 5.0V, the
output decreases, and the part requires a 0.1µF
ceramic decoupling capacitor.
Under-Voltage Lockout (UVLO)
Error Amplifier
The MP2235 has under-voltage lock-out
protection (UVLO). When the VCC voltage
exceeds the UVLO rising threshold voltage, the
MP2235 powers up. It shuts off when the VCC
voltage drops below the UVLO falling threshold
voltage. This is non-latch protection.
The error amplifier compares the FB pin voltage
to the internal 0.807V reference (VREF) and
outputs a current proportional to the difference
between the two. This output current then
charges
or
discharges
the
internal
compensation network to form the COMP
voltage, which controls the power MOSFET
current. The optimized internal compensation
network minimizes the external component
counts and simplifies the control loop design.
The MP2235 is disabled when the input voltage
falls below 3.25V. If an application requires a
higher under-voltage lockout (UVLO) threshold,
use the EN pin as shown in Figure 3 to adjust
the input voltage UVLO by using two external
resistors. For best results, set the UVLO falling
threshold (VSTOP) above 4.5V using the
enable resistors. Set the rising threshold
(VSTART) to provide enough hysteresis to
allow for any input supply variations.
Enable/SYNC Control
EN/SYNC is a digital control pin that turns the
regulator on and off. Drive EN high to turn on
the regulator; drive it low to turn it off. An
internal 1MΩ resistor from EN/SYNC to GND
allows EN/SYNC to be floated to shut down the
chip.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
10
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
Figure 4: Simplified AAM Control Logic
When the load current is light, the inductor peak
current is set internally which is about 0.9A for
VIN=12V, VOUT=3.3V, and L=3.3μH.
Figure 3: Adjustable UVLO
Soft-Start
Adjust the soft-start time by connecting a
capacitor from SS pin to ground. When the soft-
start begins, an internal 11µA current source
charges the external capacitor. During soft-
start, the soft-start capacitor connects to the
non-inverting input of the error amplifier. The
soft-start period continues until the voltage on
the soft-start capacitor exceeds the 0.8V
reference. Then the non-inverting amplifier uses
the reference voltage takes as the input. Use
the following equation to calculate the soft-start
time:
Over-Current-Protection and Hiccup
The MP2235 has a cycle-by-cycle over-current
limit when the inductor current peak value
exceeds the set current limit threshold.
Meanwhile, the output voltage drops until VFB is
below the Under-Voltage (UV) threshold—
typically 50% below the reference. Once UV is
triggered, the MP2235 enters hiccup mode to
periodically restart the part. This protection
mode is especially useful when the output is
dead-shorted to ground, and greatly reduces
the average short circuit current to alleviate
thermal issues and protect the regulator. The
MP2235 exits the hiccup mode once the over-
current condition is removed.
0.8VCss(nF)
tSS(ms)
11A
Power Save Mode for Light Load Condition
Thermal Shutdown
The
MP2235
has
AAM
(Advanced
Thermal shutdown prevents the chip from
operating at exceedingly high temperatures.
When the silicon die reaches temperatures that
exceed 150°C, it shuts down the whole chip.
When the temperature drops below its lower
threshold, typically 130°C, the chip is enabled
again.
Asynchronous Modulation) power save mode
for light load. The AAM voltage is set at 0.6V
internally. Under the heavy load condition, the
VCOMP is higher than VAAM. When clock goes
high, the high-side power MOSFET turns on
and remains on until VILsense reaches the value
set by the COMP voltage. The internal clock
resets every time when VCOMP is higher than
Floating Driver and Bootstrap Charging
An external bootstrap capacitor powers the
floating power MOSFET driver. 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 by VIN through
D1, M1, R3, C4, L1 and C2 (Figure 5). If (VIN-
VSW) exceeds 5V, U1 will regulate M1 to
maintain a 5V BST voltage across C4. A 20Ω
resistor placed between SW and BST cap. is
strongly recommended to reduce SW spike
voltage.
VAAM
.
Under the light load condition, the value of
VCOMP is low. When VCOMP is less than VAAM and
VFB is less than VREF, VCOMP ramps up until it
exceeds VAAM, during this time, the internal
clock is blocked, thus the MP2235 skips some
pulses for PFM (Pulse Frequency Modulation)
mode and achieves the light load power save.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
11
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
Figure 5: Internal Bootstrap Charging Circuit
Startup and Shutdown
If both VIN and VEN exceed their respective
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 a stable supply
for the remaining circuitries.
Three events can shut down the chip: VEN low,
VIN low, and thermal shutdown. During 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.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
12
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
APPLICATION INFORMATION
Setting the Output Voltage
The external resistor divider sets the output
voltage (see Typical Application on page 1).
1
fZ1
2RESRCOUT
1
fP1
Choose R1 around 40kΩ for VOUT>1.2V then R2
is then given by:
2RLCOUT
R1
Where ADC is the DC gain of power stage, RL is
the load resistance, Ri is the current sense
resistance (Ri=0.22Ω). RESR is the equivalent
series resistance of output capacitor. COUT is the
output capacitance.
R2
V
OUT
1
0.807V
The T-Type resistor R5 is used to control the
bandwidth of control loop which will be
introduced below.
MP2235 uses voltage type amplifier for the
feedback error amplifier and integrates
compensation to ease the system design. The
output to control transfer function is given by:
Control Loop Compensation
MP2235 employs peak current mode control for
easy compensation and fast transient response.
To simplify the compensation design and
components,
integrates internal compensation. Figure 6 shows
an equivalent model for the device control loop.
s
s
2fZ3
s
(1
)(1
)
VC
2fZ2
s
minimize
external
MP2235
AEA
VOUT
s(1
)(1
)
2fP2
2fP3
VOUT
CP
R2
AEA
VOUT
(CZ CP )(R1RT R1R2 R2RT )
1pF
CZ
RZ
CF
1
R1
R2
RESR
fZ2
300kΩ 50pF
RT
RL
2RZCZ
FB
COUT
1
fZ3
VC
2R1CF
1
fP2
2RZCP
Figure 6: Equivalent Control Loop Model
1
fP3
The device power stage can be approximated to
a voltage controlled current source (duty cycle
modulator) supplying current to the output
capacitor and load resistor. The control (VC) to
output (VOUT) transfer function is shown as below:
2(R1 //R2 //RT )CZ
Where R1, R2 are the feedback resistors, RT is
the T-type resistor between feedback resistor
divider and FB pin. CF is the type III
compensation feed forward capacitor. RZ, CZ and
CP are internal compensation resistor and
capacitors.
s
1
VOUT
VC
2fZ1
s
ADC
1
The goal of compensation design is to shape the
converter transfer function to get a desired loop
gain. The system crossover frequency where the
2fP1
RL
ADC
Ri
feedback loop has the unity gain is important.
Lower crossover frequency results in slower line
and load transient responses, while higher
crossover frequency could cause system
instability. A good rule of thumb is to set the
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
13
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
crossover frequency below one-tenth of the
switching frequency.
If large output inductor is used, like 22µH, the
phase margin will decrease a lot due to the half
switching frequency pole moves towards
crossover frequency. In this condition, it’s
suggested increasing feed forward capacitor
value of CF to get enough phase margins while
it’s better to keep the feed forward zero
frequency higher than half of crossover
frequency.
To optimize the compensation components, the
following procedure can be used.
1. Choose high-side feedback resistor R1 and
calculate the value of low-side resistor R2
according to desired output voltage. Suggest
choosing R1 around 40kΩ for >1.2V output
condition.
2. Choose the T-Type resistor RT to set the
desired crossover frequency. Determine the RT
value by the following equation:
VFB RZ
R1 R2
RT
VOUT Ri 2 fC COUT R1 R2
Figure 7: T-Type Network
RZ is the internal compensation resistor, which
equals to 300kΩ. fC is the desired crossover
frequency which is typically one tenth of the
switching frequency. Ri is the current sense
resistance, 0.22Ω.
Table 1 lists the recommended resistors and
compensation values for common output
voltages (refer to Figure 7).
Table 1: Resistor Selection for Common Output
Voltages
3. Choose feed forward capacitor CF to achieve
sufficient phase margin especially for large
output inductor condition. In theory there is no
need to add type III zero for peak current mode
control, but in real circuit there are some parasitic
capacitors or filters internal which induces poles
into the control loop. Fortunately, those poles are
locating at high frequency range which won’t
affect the step 2 bandwidth calculation while it
affects the phase margin. For applications with
typical inductor values (<4.7µH), setting the
compensation zero, fZ3 (formed by R1 and CF)
around 1.5 times of crossover frequency fC. Then
the CF value can be calculated by following
equation:
VOUT
(V)
R1 (kΩ) R2 (kΩ) Rt (kΩ) Cf(pF) L(μH)
1
20.5
30.1
40.2
40.2
40.2
40.2
84.5
61.9
32.4
19.1
13
34
24
15
6.8
5.6
2
33
33
33
33
33
33
1
1.2
1.8
2.5
3.3
5
1
2.2
2.2
3.3
3.3
7.68
For more accurate control loop design, visit MPS
website and run the online bode plot simulation
by DC/DC designer.
Selecting the Inductor
Use a 1µH-to-22µH inductor with a DC current
rating of at least 25% percent higher than the
maximum load current for most applications. For
highest efficiency, use an inductor with a DC
resistance less than 15mΩ. For most designs,
the inductance value can be derived from the
following equation.
1
CF
3R1 fC
If electrolytic capacitor is used or the output
capacitor has large ESR, the feed forward
capacitor CF is not needed any more since there
is already one ESR zero in the loop.
VOUT (V VOUT
)
IN
L1
V IL fOSC
IN
Where ΔIL is the inductor ripple current.
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
Choose the inductor ripple current to be
Selecting the Output Capacitor
approximately 30% of the maximum load
current. The maximum inductor peak current is:
The output capacitor (C2) maintains the DC
output voltage. Use ceramic, tantalum, or low-
ESR electrolytic capacitors. For best results,
use low ESR capacitors to keep the output
voltage ripple low. The output voltage ripple can
be estimated as:
IL
2
IL(MAX) ILOAD
Use a larger inductor for improved efficiency
under light-load conditions—below 100mA.
VOUT
VOUT
1
VOUT
1
R
ESR
Selecting the Input Capacitor
fS L1
V
8 fS C2
IN
The input current to the step-down converter is
discontinuous, therefore requires a capacitor is
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. Use low ESR capacitors for the best
performance. Use ceramic capacitors with X5R
or X7R dielectrics for best results because of
their low ESR and small temperature
coefficients. For most applications, use a 22µF
capacitor.
Where L1 is the inductor value and RESR is the
equivalent series resistance (ESR) value of the
output capacitor.
For ceramic capacitors, the capacitance
dominates the impedance at the switching
frequency, and the capacitance causes the
majority of the output voltage ripple. For
simplification, the output voltage ripple can be
estimated as:
Since C1 absorbs the input switching current, it
requires an adequate ripple current rating. The
RMS current in the input capacitor can be
estimated by:
VOUT
8 fS2 L1 C2
VOUT
ΔVOUT
1
V
IN
For tantalum or electrolytic capacitors, the ESR
dominates the impedance at the switching
frequency. For simplification, the output ripple
can be approximated as:
VOUT
VOUT
IC1 ILOAD
1
V
V
IN
IN
The worse case condition occurs at VIN = 2VOUT
where:
,
VOUT
VOUT
ΔVOUT
1
RESR
fS L1
VIN
ILOAD
IC1
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP2235 can be optimized for a wide range of
capacitance and ESR values.
2
For simplification, choose an input capacitor
with an RMS current rating greater than half of
the maximum load current.
The input capacitor can be electrolytic, tantalum
or ceramic. When using electrolytic or tantalum
capacitors, add a small, high quality ceramic
capacitor (e.g. 0.1μF) placed as close to the IC
as possible. When using ceramic capacitors,
make sure that they have enough capacitance
to provide sufficient charge to prevent
excessive voltage ripple at input. The input
voltage ripple caused by capacitance can be
estimated as:
ILOAD
VOUT
VOUT
V
1
IN
fS C1
VIN
V
IN
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
15
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
External Bootstrap Diode
An external bootstrap diode can enhance the
efficiency of the regulator given the following
conditions:
VOUT is 5V or 3.3V; and
VOUT
Duty cycle is high: D=
>65%
VIN
In these cases, add an external BST diode from
the VCC pin to BST pin, as shown in Figure 8.
Figure 8: Optional External Bootstrap Diode to
Enhance Efficiency
The recommended external BST diode is
IN4148, and the BST capacitor value is 0.1µF
to 1μF.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
16
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
PC Board Layout (8)
PCB layout is very important to achieve stable
operation especially for VCC capacitor and
input capacitor placement. For best results,
follow these guidelines:
VOUT
GND
EN/SYNC
BST
1. Use large ground plane directly connect to
GND pin. Add vias near the GND pin if
bottom layer is ground plane.
SW
2. Place the VCC capacitor to VCC pin and
GND pin as close as possible. Make the
trace length of VCC pin-VCC capacitor
anode-VCC capacitor cathode-chip GND
pin as short as possible.
GND
3. Place the ceramic input capacitor close to
IN and GND pins. Keep the connection of
input capacitor and IN pin as short and
wide as possible.
Design Example
Below is a design example following the
application guidelines for the specifications:
4. Route SW, BST away from sensitive
analog areas such as FB. It’s not
recommended to route SW, BST trace
under chip’s bottom side.
Table 2: Design Example
5. Place the T-type feedback resistor R5 close
to chip to ensure the trace which connects
to FB pin as short as possible
Notes:
VIN
VOUT
Io
12V
3.3V
3A
The detailed application schematic is shown in
Figure 10. The typical performance and circuit
waveforms have been shown in the Typical
Performance Characteristics section. For more
device applications, please refer to the related
Evaluation Board Datasheets.
8) The recommended layout is based on the Figure 8 Typical
Application circuit on the next page.
GND
C4
SW
C6
L1
R4
C1
C1A
Vin
C2
Vout
C2A
GND
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
17
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL APPLICATION CIRCUITS
Figure 9: 12VIN, 5V/3A Output
Figure 10: 12VIN, 3.3V/3A Output
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
18
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
Figure 11: 12VIN, 2.5V/3A Output
Figure 12: 12VIN, 1.8V/3A Output
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
19
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER
Figure 13: 12VIN, 1.2V/3A Output
Figure 14: 12VIN, 1V/3A Output
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
20
MP2235 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
PACKAGE INFORMATION
TSOT23-8
See note 7
EXAMPLE
TOP MARK
IAAAA
PIN 1 ID
RECOMMENDED LAND PATTERN
TOP VIEW
SEATING PLANE
SEE DETAIL ''A''
FRONT VIEW
SIDE VIEW
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.
DETAIL ''A''
5) JEDEC REFERENCE IS MO-193, VARIATION BA.
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)
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.
MP2235 Rev. 1.0
5/16/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
21
相关型号：
MP2235SGJ-Z
Switching Regulator, Current-mode, 2000kHz Switching Freq-Max, PDSO8, TSOT-23, 8-PIN
MPS
MP2259DJ-LF
Switching Regulator, Current-mode, 1.8A, 1400kHz Switching Freq-Max, PDSO6, ROHS COMPLIANT, MO-193AB, TSOT-23, 6 PIN
MPS
MP2259DJ-LF-Z
Switching Regulator, Current-mode, 1.8A, 1400kHz Switching Freq-Max, PDSO6, ROHS COMPLIANT, MO-193AB, TSOT-23, 6 PIN
MPS
©2020 ICPDF网 联系我们和版权申明