MPS MP2358DS 2a, 23v, 370khz step-down converter Datasheet

TM
MP2358
2A, 23V, 370KHz
Step-Down Converter
The Future of Analog IC Technology
TM
DESCRIPTION
FEATURES
The MP2358 is a monolithic step-down switch
mode converter with a built-in internal power
MOSFET. It achieves 2A continuous output
current over a wide input supply range with
excellent load and line regulation.
•
•
•
2A Output Current with QFN Package
0.18Ω Internal Power MOSFET Switch
Stable with Low ESR Output Ceramic
Capacitors
93% Efficiency
23µA Shutdown Mode
Fixed 370KHz Frequency
Thermal Shutdown
Cycle-by-Cycle Over Current Protection
Wide 4.75V to 23V Operating Input Range
Output Adjustable from 0.92V to 16V
Programmable Under Voltage Lockout
Available in QFN10 (3mm x 3mm) and SO8
Packages
Fault condition protection includes cycle-by-cycle
current limiting and thermal shutdown. In
shutdown mode the regulator draws 23µA of
supply
current.
Programmable
soft-start
minimizes the inrush supply current and the
output overshoot at initial startup.
•
•
•
•
•
•
•
•
•
The MP2358 requires a minimum number of
readily available standard external components.
APPLICATIONS
Current mode operation provides fast transient
response and eases loop stabilization.
•
•
•
EVALUATION BOARD REFERENCE
Board Number
Dimensions
EV2358DS-00A
EV2358DQ-00A
2.3” x 1.4” x 0.5”
2.0” x 1.3” x 0.4”
Distributed Power Systems
Battery Charger
Pre-Regulator for Linear Regulators
“MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic
Power Systems, Inc.
TYPICAL APPLICATION
Efficiency vs
Output Current
INPUT
4.75V - 23V
95
C5
10nF
OPEN = AUTOMATIC
STARTUP
SW
EN
MP2358
SS
D1
B220A
VOUT
3.3V/2A
FB
GND
C4
10nF
90
BS
C6
OPEN
COMP
C3
3.9nF
EFFICIENCY (%)
IN
5.0V
3.3V
85
2.5V
80
75
70
65
60
MP2358_TAC_S01
0
0.5
1.0
1.5
2.0
2.5
OUTPUT CURRENT (A)
MP2358_EC01
MP2358 Rev. 1.3
3/23/2006
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1
TM
MP2358 – 2A, 23V, 370KHz STEP-DOWN CONVERTER
PACKAGE REFERENCE
TOP VIEW
TOP VIEW
NC
1
10
SS
BS
2
9
EN
NC
3
8
COMP
IN
4
7
FB
SW
5
6
GND
BS
1
8
SS
IN
2
7
EN
SW
3
6
COMP
GND
4
5
FB
MP2358_PD02_SOIC8
EXPOSED PAD
ON BACKSIDE
MP2358_PD01-QFN10
Part Number*
Package
Temperature
Part Number**
Package
Temperature
MP2358DQ
QFN10
(3mm x 3mm)
–40°C to +85°C
MP2358DS
SOIC8
–40°C to +85°C
*
** For Tape & Reel, add suffix –Z (eg. MP2358DS–Z)
For Tape & Reel, add suffix –Z (eg. MP2358DQ–Z)
For Lead Free, add suffix –LF (eg. MP2358DQ–LF–Z)
For Lead Free, add suffix –LF (eg. MP2358DS–LF–Z)
ABSOLUTE MAXIMUM RATINGS (1)
Recommended Operating Conditions
Supply Voltage (VIN)..................................... 25V
Switch Node Voltage (VSW) .......................... 26V
Bootstrap Voltage (VBS) ....................... VSW + 6V
Feedback Voltage (VFB) .................–0.3V to +6V
Enable/UVLO Voltage (VEN)...........–0.3V to +6V
Comp Voltage (VCOMP) ...................–0.3V to +6V
SS Voltage (VSS) ............................–0.3V to +6V
Junction Temperature ............................ +150°C
Lead Temperature ................................. +260°C
Storage Temperature.............. –65°C to +150°C
Supply Voltage (VIN) ...................... 4.75V to 23V
Operating Temperature.................–40°C to +85°C
Thermal Resistance
(3)
θJA
(2)
θJC
QFN10 (3x3)........................... 50 ...... 12... °C/W
SOIC8.................................... 105 ..... 50... °C/W
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 approximately 1” square of 1 oz copper.
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameter
Feedback Voltage
Upper Switch On Resistance
Lower Switch On Resistance
Upper Switch Leakage
Current Limit (4)
Current Sense Transconductance
Output Current to Comp Pin Voltage
Error Amplifier Voltage Gain
Error Amplifier Transconductance
Oscillator Frequency
Short Circuit Frequency
Soft-Start Pin Equivalent
Output Resistance
MP2358 Rev. 1.3
3/23/2006
Symbol Condition
VFB
4.75V ≤ VIN ≤ 23V
RDS(ON)1
RDS(ON)2
VEN = 0V, VSW = 0V
Min
0.892
2.8
Max
0.948
10
1.95
GCS
AVEA
GEA
fS
Typ
0.920
0.18
10
0
3.4
∆IC = ±10µA
VFB = 0V
550
400
830
370
240
9
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Units
V
Ω
Ω
µA
A
A/V
1150
V/V
µA/V
KHz
KHz
kΩ
2
TM
MP2358 – 2A, 23V, 370KHz STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS (continued)
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameter
Maximum Duty Cycle
Minimum On Time
EN Shutdown Threshold
Enable Pull Up Current
EN UVLO Threshold Rising
EN UVLO Threshold Hysteresis
Symbol Condition
DMAX VFB = 0.8V
tON
ICC > 100µA
VEN = 0V
VEN Rising
Min
0.7
2.37
Typ
90
100
1.0
1.0
2.50
210
Max
1.3
2.62
Units
%
ns
V
µA
V
mV
Supply Current (Shutdown)
VEN ≤ 0.4V
23
36
µA
Supply Current (Quiescent)
VEN ≥ 3V
1.1
1.3
mA
Thermal Shutdown
160
°C
Note:
4) Slope compensation changes current limit above 40% duty cycle.
PIN FUNCTIONS
QFN10 SOIC8
Pin #
Pin #
1
2
1
3
4
2
5
6
3
4
7
5
8
6
9
7
10
8
MP2358 Rev. 1.3
3/23/2006
Name Description
NC
BS
No Connect.
Bootstrap. This capacitor (C5) is needed to drive the power switch’s gate above the
supply voltage. It is connected between the SW and BS pins to form a floating supply
across the power switch driver. The voltage across C5 is about 5V and is supplied by
the internal +5V supply when the SW pin voltage is low.
NC
No Connect.
IN
Supply Voltage. The MP2358 operates from a +4.75V to +23V unregulated input. C1
is needed to prevent large voltage spikes from appearing at the input.
SW Switch. This connects the inductor to either IN through M1 or to GND through M2.
GND 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.
FB
Feedback. An external resistor divider from the output to GND, tapped to the FB pin,
sets the output voltage. To prevent current limit runaway during a short circuit fault
condition the frequency foldback comparator lowers the oscillator frequency when the
FB voltage is below 400mV.
COMP Compensation. This node is the output of the transconductance error amplifier and the input
to the current comparator. Frequency compensation is done at this node by connecting a
series R-C to ground. See the compensation section for exact details.
EN
Enable/UVLO. A voltage greater than 2.62V enables operation. Leave EN
unconnected if unused. An Under Voltage Lockout (UVLO) function can be
implemented by the addition of a resistor divider from VIN to GND. For complete low
current shutdown the EN pin voltage needs to be less than 700mV.
SS
Soft-Start. Connect SS to an external capacitor to program the soft-start. If unused,
leave it open.
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TM
MP2358 – 2A, 23V, 370KHz STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT = 3.3V, TA = +25°C, unless otherwise noted.
Steady State
Startup
IOUT = 2A
No Load
VIN AC
500mV/div.
VEN
10V/div.
VOUT AC
50mV/div.
VOUT
2V/div.
VSW
10V/div.
VSW
10V/div.
IL
2A/div.
IL
1A/div.
4ms/div.
MP2358-TPC01
MP2358-TPC02
Startup
Startup
1A Load
2A Load
VEN
10V/div.
VEN
10V/div.
VOUT
2V/div.
VOUT
2V/div.
VSW
10V/div.
VSW
10V/div.
IL
1A/div.
IL
1A/div.
4ms/div.
4ms/div.
MP2358-TPC03
MP2358-TPC04
VOUT AC
500mV/div.
IL
1A/div.
IOUT
1A/div.
MP2358-TPC05
MP2358 Rev. 1.3
3/23/2006
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TM
MP2358 – 2A, 23V, 370KHz STEP-DOWN CONVERTER
OPERATION
MP2358 reverts to its initial M1 off, M2 on state.
If the Current Sense Amplifier plus Slope
Compensation signal does not exceed the
COMP voltage, then the falling edge of the CLK
resets the Flip-Flop.
The MP2358 is a current mode regulator. That
is, the COMP pin voltage is proportional to the
peak inductor current. At the beginning of a
cycle: the upper transistor M1 is off; the lower
transistor M2 is on (see Figure 1); the COMP
pin voltage is higher than the current sense
amplifier output; and the current comparator’s
output is low. The rising edge of the 370KHz
CLK signal sets the RS Flip-Flop. Its output
turns off M2 and 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 Current Sense
Amplifier output and compared to the Error
Amplifier output by the Current Comparator.
When the Current Sense Amplifier plus Slope
Compensation signal exceeds the COMP pin
voltage, the RS Flip-Flop is reset and the
The output of the Error Amplifier integrates the
voltage difference between the feedback and
the 0.92V bandgap reference. The polarity is
such that a FB pin voltage lower than 0.92V
increases the COMP pin voltage. Since the
COMP pin voltage is proportional to the peak
inductor current an increase in its voltage
increases current delivered to the output. The
lower 10Ω switch ensures that the bootstrap
capacitor voltage is charged during light load
conditions. External Schottky Diode D1 carries
the inductor current when M1 is off.
IN
CURRENT
SENSE
AMPLIFIER
INTERNAL
REGULATORS
OSCILLATOR
240KHz/
370KHz
1.0V
--
EN
-2.50V/
2.29V
+
FREQUENCY
FOLDBACK
COMPARATOR
SLOPE
COMP
5V
-BS
CLK
+
+
+
SHUTDOWN
COMPARATOR
--
S
Q
R
Q
CURRENT
COMPARATOR
SW
LOCKOUT
COMPARATOR
--
+
--
0.4V
0.92V
FB
+
SS
1.8V
GND
ERROR
AMPLIFIER
COMP
MP2358_BD01
Figure 1—Functional Block Diagram
MP2358 Rev. 1.3
3/23/2006
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5
TM
MP2358 – 2A, 23V, 370KHz STEP-DOWN CONVERTER
APPLICATION INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
The output voltage is set using a resistive voltage
divider from the output voltage to FB pin. The
voltage divider divides the output voltage down to
the feedback voltage by the ratio:
VFB = VOUT
R2
R1 + R2
Where VFB is the feedback voltage and VOUT is
the output voltage.
Thus the output voltage is:
VOUT = 0.92 ×
R1 + R2
R2
A typical value for R2 can be as high as 100kΩ,
but a typical value is 10kΩ. Using that value, R1
is determined by:
R1 = 10.87 × ( VOUT − 0.92)
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 25.8kΩ.
Inductor
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value inductor
will result in less ripple current that will result in
lower output ripple voltage. However, the larger
value inductor will have a larger physical size,
higher series resistance, and/or lower saturation
current. A good rule for determining the
inductance to use is to allow the peak-to-peak
ripple current in the inductor to be approximately
30% of the maximum switch current limit. Also,
make sure that the peak inductor current is below
the maximum switch current limit. The inductance
value can be calculated by:
L=
⎛
⎞
VOUT
V
× ⎜⎜1 − OUT ⎟⎟
fS × ∆IL ⎝
VIN ⎠
Where fS is the switching frequency, ∆IL is the
peak-to-peak inductor ripple current and VIN is
the input voltage.
MP2358 Rev. 1.3
3/23/2006
Choose an inductor that will not saturate under
the maximum inductor peak current. The peak
inductor current can be calculated by:
ILP = ILOAD +
⎛
VOUT
V
× ⎜⎜1 − OUT
2 × fS × L ⎝
VIN
⎞
⎟⎟
⎠
Where ILOAD is the load current.
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.
Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. Use low ESR capacitors for the best
performance. Ceramic capacitors are preferred,
but tantalum or low-ESR electrolytic capacitors
may also suffice.
Since the input capacitor absorbs the input
switching current it requires an adequate ripple
current rating. The RMS current in the input
capacitor can be estimated by:
I C 2 = ILOAD ×
VOUT ⎛⎜ VOUT
× 1−
VIN ⎜⎝
VIN
⎞
⎟
⎟
⎠
The worst-case condition occurs at VIN = 2VOUT,
where:
I C2 =
ILOAD
2
For simplification, choose the input capacitor
whose RMS current rating greater than half of
the maximum load current.
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TM
MP2358 – 2A, 23V, 370KHz STEP-DOWN CONVERTER
The input capacitor can be electrolytic, tantalum
or ceramic. When using electrolytic or tantalum
capacitors, a small, high quality ceramic
capacitor, i.e. 0.1µF, should be 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 by:
∆VIN =
⎛
ILOAD
V
V
× OUT × ⎜1 − OUT
fS × C1 VIN ⎜⎝
VIN
⎞
⎟⎟
⎠
Where C1 is the input capacitance value.
Output Capacitor
The output capacitor is required to maintain the
DC output voltage. Ceramic, tantalum, or low
ESR electrolytic capacitors are recommended.
Low ESR capacitors are preferred to keep the
output voltage ripple low. The output voltage
ripple can be estimated by:
∆VOUT =
VOUT ⎛
V
× ⎜1 − OUT
f S × L ⎜⎝
VIN
⎞
⎞ ⎛
1
⎟
⎟⎟ × ⎜ R ESR +
⎜
⎟
8
×
f
×
C
2
S
⎠ ⎝
⎠
Where L is the inductor value, RESR is the
equivalent series resistance (ESR) value of the
output capacitor and C2 is the output
capacitance value.
In the case of ceramic capacitors, the
impedance at the switching frequency is
dominated by the capacitance. The output
voltage ripple is mainly caused by the
capacitance. For simplification, the output
voltage ripple can be estimated by:
∆VOUT =
⎛
V
× ⎜⎜1 − OUT
VIN
× L × C2 ⎝
VOUT
8 × fS
2
⎞
⎟⎟
⎠
In the case of tantalum or electrolytic
capacitors, the ESR dominates the impedance
at the switching frequency. For simplification,
the output ripple can be approximated to:
∆VOUT =
VOUT ⎛
V
⎞
× ⎜1 − OUT ⎟ × RESR
fS × L ⎝
VIN ⎠
Compensation Components
The MP2358 employs current mode control for
easy compensation and fast transient response.
The system stability and transient response are
controlled through the COMP pin. COMP pin is
the output of the internal transconductance
error amplifier. A series capacitor-resistor
combination sets a pole-zero combination to
control the characteristics of the control system.
The DC gain of the voltage feedback loop is
given by:
A VDC = R LOAD × G CS × A VEA ×
VFB
VOUT
Where RLOAD is the load resistor value, GCS is
the current sense transconductance and AVEA is
the error amplifier voltage gain.
The system has two poles of importance. One
is due to the compensation capacitor (C3) and
the output resistor of error amplifier, and the
other is due to the output capacitor and the load
resistor. These poles are located at:
fP1 =
GEA
2π × C3 × A VEA
fP2 =
1
2π × C2 × R LOAD
Where
GEA
is
transconductance.
the
error
amplifier
The system has one zero of importance, due to the
compensation
capacitor
(C3)
and
the
compensation resistor (R3). This zero is located at:
f Z1 =
1
2π × C3 × R3
The system may have another zero of
importance, if the output capacitor has a large
capacitance and/or a high ESR value. The zero,
due to the ESR and capacitance of the output
capacitor, is located at:
fESR =
1
2π × C2 × R ESR
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP2358 can be optimized for a wide range of
capacitance and ESR values.
MP2358 Rev. 1.3
3/23/2006
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TM
MP2358 – 2A, 23V, 370KHz STEP-DOWN CONVERTER
In this case, a third pole set by
compensation capacitor (C6) and
compensation resistor (R3) is used
compensate the effect of the ESR zero on
loop gain. This pole is located at:
f P3 =
the
the
to
the
1
2π × C6 × R3
The goal of compensation design is to shape
the converter transfer function to get a desired
loop gain. The system crossover frequency
where the feedback loop has the unity gain is
important.
Lower crossover frequencies result in slower
line and load transient responses, while higher
crossover frequencies could cause the system
to become unstable. A good rule of thumb is to
set the crossover frequency to below one-tenth
of the switching frequency. To optimize the
compensation components, the following
procedure can be used:
1. Choose the compensation resistor (R3) to set
the desired crossover frequency. Determine the
R3 value by the following equation:
R3 =
2π × C2 × f C VOUT
×
G EA × G CS
VFB
Where fC is the desired crossover frequency,
which is typically less than one tenth of the
switching frequency.
2. Choose the compensation capacitor (C3) to
achieve the desired phase margin. For
applications with typical inductor values, setting
the compensation zero, fZ1, to below one forth
of the crossover frequency provides sufficient
phase margin. Determine the C3 value by the
following equation:
C3 >
3. Determine if the second compensation
capacitor (C6) is required. It is required if the
ESR zero of the output capacitor is located at
less than half of the switching frequency, or the
following relationship is valid:
f
1
< S
2π × C2 × R ESR
2
If this is the case, then add the second
compensation capacitor (C6) to set the pole fP3
at the location of the ESR zero. Determine the
C6 value by the equation:
C6 =
C2 × R ESR
R3
External Bootstrap Diode
It is recommended that an external boost diode
be added when the system has a 5V fixed input
or the power supply generates a 5V output.
This helps improve the efficiency of the
MP2358 regulator. The bootstrap diode can be
a low cost one such as IN4148 or BAT54.
5V
BS
10nF
MP2358
SW
MP2358_F02
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty
cycle operation (when
VOUT
>65%) and high
VIN
output voltage (VOUT>12V) applications.
2
π × R3 × f C
Where R3 is the compensation resistor value.
MP2358 Rev. 1.3
3/23/2006
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TM
MP2358 – 2A, 23V, 370KHz STEP-DOWN CONVERTER
PACKAGE INFORMATION
QFN10 (3mm x 3mm)
0.35
0.45
2.95
3.05
Pin 1
Identif ication
0.20
0.30
Pin 1
Identif ication
R0.200TY P
10
1
QFN10L
(3 x 3mm)
2.95
3.05
2.35
2.000
2.45
Ref Exp. DAP
0.500
Bsc
6
5
1.65
1.75
Exp. DAP
Top View
BottomView
0.85
0.95
0.178
0.228
0.0000.050
Side View
Note:
1) Dimensions arein millimeters.
SOIC8
PIN 1 IDENT.
0.229(5.820)
0.244(6.200)
0.0075(0.191)
0.0098(0.249)
0.150(3.810)
0.157(4.000)
SEE DETAIL "A"
0.011(0.280) x 45o
0.020(0.508)
0.013(0.330)
0.020(0.508)
0.050(1.270)BSC
0.189(4.800)
0.197(5.004)
0.053(1.350)
0.068(1.730)
0o-8o
0.049(1.250)
0.060(1.524)
0.016(0.410)
0.050(1.270)
DETAIL "A"
SEATING PLANE
0.001(0.030)
0.004(0.101)
NOTE:
1) Control dimension is in inches. Dimension in bracket is millimeters.
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.
MP2358 Rev. 1.3
3/23/2006
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© 2006 MPS. All Rights Reserved.
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