MIC22405 DATA SHEET (11/05/2015) DOWNLOAD

MIC22405
4A Integrated Switch High-Efficiency
Synchronous Buck Regulator with
Frequency Programmable upto 4MHz
General Description
Features
The Micrel MIC22405 is a high efficiency, 4A integrated
switch synchronous buck (step-down) regulator. The
MIC22405 is optimized for highest efficiency, achieving
more than 95% efficiency while still switching at 1MHz.
The ultra-high speed control loop keeps the output voltage
within regulation even under the extreme transient load
swings commonly found in FPGAs and low-voltage ASICs.
The output voltage is pre-bias safe and can be adjusted
down to 0.7V to address all low-voltage power needs.
The MIC22405 offers a full range of sequencing and
tracking options. The Enable/Delay (EN/DLY) pin,
combined with the Power Good (PG) pin, allows multiple
outputs to be sequenced in any way during turn-on and
turn-off. The Ramp Control™ (RC) pin allows the device to
be connected to another product in the MIC22xxx and/or
MIC68xxx family, to keep the output voltages within a
certain ∆V on start-up.
®
The MIC22405 is available in a 20-pin 3mm x 4mm MLF
with a junction operating range from –40°C to +125°C.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
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Input voltage range: 2.9V to 5.5V
Output voltage adjustable down to 0.7V
Output load current up to 4A
Safe start-up into a pre-biased output
Full sequencing and tracking capability
Power Good output
Efficiency > 95% across a broad load range
Programmable frequency 300kHz to 4MHz
Ultra-fast transient response
Easy RC compensation
100% maximum duty cycle
Fully-integrated MOSFET switches
Thermal shutdown and current-limit protection
20-pin 3mm x 4mm MLF®
–40°C to +125°C junction temperature range
Applications
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High power density point-of-load conversion
Servers, routers, and base stations
DVD recorders / Blu-ray players
Computing peripherals
FPGAs, DSP and low voltage ASIC power
_________________________________________________________________________________________________________________________
Typical Application
Efficiency (VIN = 5.0V)
vs. Output Current
100
3.3V
EFFICIENCY (%)
95
90
1.8V
85
80
V IN = 5.0V
75
70
MIC22405 4A 1MHz Synchronous Output Converter
0
1
2
3
4
OUTPUT CURRENT (A)
Ramp Control is a trademark of Micrel, Inc
MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
May 2011
M9999-061511-A
Micrel, Inc.
MIC22405
Ordering Information
Part Number
Voltage
MIC22405YML
Adjustable
Junction Temperature Range
–40° to +125°C
Package
Lead Finish
®
20-Pin 3x4 MLF *
Pb-Free
Note:
®
1. MLF
is a GREEN ROHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configuration
20-Pin 3mm x 4mm MLF® (ML)
Pin Description
Pin Number
Pin Name
Description
1
PG
PG (Output): This is an open drain output that indicates when the output voltage is below 90% of
its nominal voltage. The PG flag is asserted without delay when the enable is set low or when the
output goes below the 90% threshold.
2
CF
Adjustable frequency with external capacitor. Refer to table 2.
Compensation Pin (Input): The MIC22405 uses an internal compensation network containing a
fixed-frequency zero (phase lead response) and pole (phase lag response) which allows the
external compensation network to be much simplified for stability. The addition of a single
capacitor and resistor to the COMP pin will add the necessary pole and zero for voltage mode
loop stability using low-value, low-ESR ceramic capacitors.
4
COMP
6
FB
7
SGND
Signal Ground: Internal signal ground for all low power circuits.
8
SVIN
Signal Power Supply Voltage (Input): This pin is connected externally to the PVIN pin. A 2.2µF
ceramic capacitor from the SVIN pin to SGND must be placed next to the IC.
10, 17
PVIN
Power Supply Voltage (Input): The PVIN pins are the input supply to the internal P-Channel
Power MOSFET. A 22µF ceramic is recommended for bypassing at each PVIN pin. The SVIN
pin must be connected to a PVIN pin.
11, 16
PGND
Power Ground: Internal ground connection to the source of the internal N-Channel MOSFETs.
12, 13, 14, 15
SW
June 2011
Feedback: Input to the error amplifier. The FB pin is regulated to 0.7V. A resistor divider
connecting the feedback to the output is used to adjust the desired output voltage.
Switch (Output): This is the connection to the drain of the internal P-Channel MOSFET and drain
of the N-Channel MOSFET. This is a high-frequency, high-power connection; therefore traces
should be kept as short and as wide as practical.
2
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Micrel, Inc.
MIC22405
Pin Description (Continued)
Pin Number
Pin Name
18
EN/DLY
19
NC
20
RC
EP
GND
June 2011
Description
Enable/Delay (Input): This pin is internally fed with a 1µA current source from SVIN. A delayed
turn on is implemented by adding a capacitor to this pin. The delay is proportional to the
capacitor value. The internal circuits are held off until EN/DLY reaches the enable threshold of
1.24V. This pin is pulled low when the input voltage is lower than the UVLO threshold.
No Connect: Leave this pin open. Do not connect to ground or route other signal through this.
Ramp Control: A capacitor from the RC pin-to-ground determines slew rate of output voltage
during start-up. The RC pin is internally fed with a 1µA current source. The output voltage tracks
the RC pin voltage. The slew rate is proportional by the internal 1µA source and RC pin
capacitor. This feature can be used for tracking capability as well as soft start.
Exposed Pad (Power): Must be connected to the GND plane for full output power to be realized.
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M9999-061511-A
Micrel, Inc.
MIC22405
Absolute Maximum Ratings(1, 2)
Operating Ratings(3)
PVIN to PGND.................................................... –0.3V to 6V
SVIN to PGND..................................................–0.3V to PVIN
VSW to PGND...................................................–0.3V to PVIN
VEN/DLY to PGND .............................................. -0.3V to PVIN
VPG to PGND ...................................................–0.3V to PVIN
Junction Temperature ................................................ 150°C
PGND to SGND ............................................. –0.3V to 0.3V
Storage Temperature Range ....................–65°C to +150°C
Lead Temperature (soldering, 10s)............................ 260°C
ESD Rating.................................................................Note 2
Supply Voltage (PVIN/SVIN) .............................. 2.9V to 5.5V
Power Good Voltage (VPG)...................................0V to PVIN
Enable Input (VEN/DLY)...........................................0V to PVIN
Junction Temperature (TJ) ..................–40°C ≤ TJ ≤ +125°C
Package Thermal Resistance
3mm x 4mm MLF®-20 (θJC)................................25°C/W
3mm x 4mm MLF®-20 (θJA)................................55°C/W
Electrical Characteristics(4)
SVIN = PVIN = VEN/DLY = 3.3V, VOUT = 1.8V, TA = 25°C, unless noted. Bold values indicate –40°C< TJ < +125°C.
Parameter
Condition
Min.
PVIN Rising
2.9
2.55
Typ.
Max.
Units
5.5
2.9
V
V
mV
mA
µA
Power Input Supply
Input Voltage Range (PVIN)
Under-voltage Lockout Trip Level
UVLO Hysteresis
Quiescent Supply Current
Shutdown Current
Reference
Feedback Reference Voltage
Load Regulation
Line Regulation
FB Bias Current
Enable Control
EN/DLY Threshold Voltage
EN Hysteresis
EN/DLY Bias Current
RC Ramp Control
RC Pin Source Current
Oscillator
Switching Frequency
Maximum Duty Cycle
Short Current Protection
Current Limit
Internal FETs
VFB = 0.9V (not switching)
VEN/DLY = 0V
2.78
420
1.3
5
2
10
0.686
0.7
0.2
0.2
1
0.714
V
%
%
nA
1.14
1.34
1.8
V
mV
µA
IOUT = 100mA to 4A
VIN = 2.9V to 5.5V; IOUT = 100mA
VFB = 0.5V
VEN/DLY = 0.5V; VIN = 2.9V and VIN = 5.5V
0.6
1.24
10
1.0
VRC = 0.35V
0.5
1.0
1.7
µA
1.0
1.2
VFB ≤ 0.5V
0.8
100
MHz
%
VFB = 0.5V
4
7.8
14
A
Top MOSFET RDS(ON)
VFB = 0.5V, ISW = 1A
60
mΩ
Bottom MOSFET RDS(ON)
VFB = 0.9V, ISW = -1A
35
mΩ
Power Good (PG)
PG Threshold
Threshold % of VFB from VREF
Hysteresis
PG Output Low Voltage
IPG = 5mA (sinking), VEN/DLY = 0V
PG Leakage Current
VPG = 5.5V; VFB = 0.9V
June 2011
−7.5
−10
−12.5
2.0
%
135
mV
1.0
2.0
4
%
μA
M9999-061511-A
Micrel, Inc.
MIC22405
Electrical Characteristics(4) (Continued)
VIN = PVIN = VEN/DLY = 3.3V, VOUT = 1.8V, TA = 25°C, unless noted. Bold values indicate –40°C< TJ < +125°C.
Parameter
Thermal Protection
Over-temperature Shutdown
Over-temperature Shutdown
Hysteresis
Condition
Min.
TJ Rising
Typ.
Max.
Units
150
°C
10
°C
Notes:
1.
Exceeding the absolute maximum rating may damage the device.
2.
Devices are ESD sensitive. Handling precautions recommended.
3.
The device is not guaranteed to function outside its operating rating.
4.
Specification for packaged product only.
June 2011
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M9999-061511-A
Micrel, Inc.
MIC22405
Typical Characteristics
0.710
14
12
VOUT = 1.8V
IOUT = 0A
SWITCHING
8
8
6
4
VEN/DLY = 0V
2
2.5
3.0
3.5
4.0
4.5
5.0
3.0
0.702
0.698
V OUT = 1.8V
0.694
3.5
4.0
4.5
5.0
5.5
2.5
3.0
INPUT VOLTAGE (V)
0.6%
3.5
4.0
4.5
5.0
5.5
5.0
5.5
INPUT VOLTAGE (V)
Switching Frequency
vs. Input Voltage
Current Limit
vs. Input Voltage
Load Regulation
vs. Input Voltage
20
1100
V OUT = 1.8V
1050
0.2%
0.0%
VOUT = 1.8V
IOUT = 0A to 4A
-0.2%
-0.4%
15
1000
950
10
900
5
VOUT = 1.8V
850
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
800
2.5
3.0
INPUT VOLTAGE (V)
3.5
4.0
4.5
5.0
2.5
5.5
VPG THRESHOLD/VREF (%)
ENABLE INPUT CURRENT
(µA)
1.00
1.30
0.75
1.20
0.50
1.10
0.25
1.00
V EN/DLY = 0V
0.00
3.5
4.0
4.5
INPUT VOLTAGE (V)
June 2011
5.0
5.5
4.5
12.0
1.25
1.40
4.0
Power Good Threshold/VREF
Ratio vs. Input Voltage
1.50
Rising
3.5
INPUT VOLTAGE (V)
Enable Input Current
vs. Input Voltage
1.50
3.0
3.0
INPUT VOLTAGE (V)
Enable Threshold
vs. Input Voltage
2.5
IOUT = 0A
SWITCHING FREQUENCY
(kHz)
0.4%
CURRENT LIMIT (A)
TOTAL REGULATION (%)
0.706
0.690
2.5
5.5
INPUT VOLTAGE (V)
ENABLE THRESHOLD (V)
FEEDBACK VOLTAGE (V)
16
10
Feedback Voltage
vs. Input Voltage
10
SHUTDOWN CURRENT (µA)
18
SUPPLY CURRENT (mA)
VIN Shutdown Current
vs. Input Voltage
VIN Operating Supply Current
vs. Input Voltage
11.0
10.0
9.0
VREF = 0.7V
8.0
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
6
5.0
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
M9999-061511-A
Micrel, Inc.
MIC22405
Typical Characteristics (Continued)
VIN Operating Supply Current
vs. Temperature
15
12.0
10.0
VIN =3.3V
VOUT = 1.8V
IOUT = 0A
SWITCHING
8.0
Rising
IOUT = 0A
12
VEN/DLY =
0V
9
6
3
0
6.0
-25
0.750
0
25
50
75
100
-25
0
25
50
75
100
125
-50
0
25
50
75
Load Regulation
vs. Temperature
Line Regulation
vs. Temperature
0.2%
0.6%
LOAD REGULATION (%)
0.710
0.690
0.670
0.650
0.4%
0.2%
0.0%
VIN = 3.3V
VOUT = 1.8V
-0.2%
0
25
50
75
100
125
-50
-25
0
25
50
75
100
IOUT = 0A
125
-0.2%
-50
1000
950
900
VIN = 3.3V
VOUT = 1.8V
IOUT = 0A
800
50
75
TEMPERATURE (°C)
100
125
50
75
100
125
100
125
15
VIN = 3.3V
1.26
1.24
1.22
1.20
VIN = 3.3V
1.18
1.16
25
25
Current Limit
vs. Temperature
CURRENT LIMIT (A)
ENABLE THRESHOLD (V)
SWITCHING FREQUENCY
(kHz)
1050
0
TEMPERATURE (°C)
1.28
0
-25
Enable Threshold
vs. Temperature
1100
850
VIN = 2.9V to 5.5V
VOUT = 1.8V
TEMPERATURE (°C)
Switching Frequency
vs. Temperature
125
0.0%
IOUT = 0A to 4A
TEMPERATURE (°C)
100
0.1%
-0.1%
-0.4%
June 2011
-25
Feedback Voltage
vs. Temperature
VOUT = 1.8V
-25
2.2
TEMPERATURE (°C)
IOUT = 0A
-50
Falling
2.4
TEMPERATURE (°C)
VIN = 3.3V
-25
2.6
TEMPERATURE (°C)
0.730
-50
2.8
2.0
-50
125
LINE REGULATION (%)
-50
FEEDBACK VOLTAGE (V)
3.0
VIN = 3.3V
VIN THRESHOLD (V)
SHUTDOWN CURRENT (uA)
SUPPLY CURRENT (mA)
14.0
VIN UVLO Threshold
vs. Temperature
VIN Shutdown Current
vs. Temperature
VOUT = 1.8V
10
5
0
-50
-25
0
25
50
75
TEMPERATURE (°C)
7
100
125
-50
-25
0
25
50
75
TEMPERATURE (°C)
M9999-061511-A
Micrel, Inc.
MIC22405
Typical Characteristics (Continued)
Feedback Voltage
vs. Output Current
Efficiency
vs. Output Current
FEEDBACK VOLTAGE (V)
VIN =5.0V
85
80
75
70
65
VOUT = 1.8V
60
VIN = 2.9V to 5.5V
0.715
0.705
0.695
VIN = 3.3V
0.685
55
0.675
50
0
1
2
3
1
2
4.3
0
4
OUTPUT VOLTAGE (V)
IOUT = 0A
950
3.8
2
3
VIN = 5.0V
VFB < 0.8V
VFB < 0.8V
TA
25ºC
85ºC
125ºC
1.25
IC POWER DISSIPATION (W)
100
95
90
2.5V
1.8V
1.5V
1.2V
1.0V
0.9V
0.8V
0.7V
85
80
75
70
VIN = 3.3V
65
1
2
3
1
2
3
4
OUTPUT CURRENT (A)
June 2011
5.0
TA
25ºC
85ºC
125ºC
4.5
4
0
0.50
0.25
5
6
3
4
80
2.5V
1.8V
1.5V
1.2V
1.0V
0.9V
0.8V
0.7V
0.75
2
Case Temperature* (VIN = 3.3V)
vs. Output Current
IC Power Dissipation (VIN = 3.3V)
vs. Output Current
1.00
1
OUTPUT CURRENT (A)
VIN = 3.3V
0.00
0
5.5
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Efficiency (VIN = 3.3V)
vs. Output Current
4
4.0
0
4
3
Output Voltage (VIN = 5.0V)
vs. Output Current
6.0
3.3
2.8
2
VIN = 3.3V
2.3
900
1
1
OUTPUT CURRENT (A)
OUTPUT VOLTAGE (V)
SWITCHING FREQUENCY
(kHz)
VOUT = 1.8V
1000
EFFICIENCY (%)
3
Output Voltage (VIN = 3.3V)
vs. Output Current
VIN = 3.3V
0
0.00%
OUTPUT CURRENT (A)
Switching Frequency
vs. Output Current
1050
0.02%
-0.02%
0
4
OUTPUT CURRENT (A)
1100
VOUT = 1.8V
0.04%
VOUT = 1.8V
CASE TEMPERATURE (°C)
EFFICIENCY (%)
90
Line Regulation
vs. Output Current
0.06%
0.725
VIN =3.3V
95
LINE REGULATION (%)
100
60
40
VIN = 3.3V
20
VOUT = 1.8V
0
0
1
2
3
OUTPUT CURRENT (A)
8
4
0
1
2
3
4
OUTPUT CURRENT (A)
M9999-061511-A
Micrel, Inc.
MIC22405
Typical Characteristics (Continued)
Efficiency (VIN = 5.0V)
vs. Output Current
IC Power Dissipation (VIN = 5.0V)
vs. Output Current
100
80
3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
0.9V
0.8V
0.7V
90
85
80
75
VIN = 5.0V
70
3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
0.9V
0.8V
0.7V
0.96
0.72
0.48
DIE TEMPERATURE (°C)
IC POWER DISSIPATION (W)
1.20
95
EFFICIENCY (%)
Case Temperature* (VIN = 5.0V)
vs. Output Current
0.24
1
2
3
4
OUTPUT CURRENT (A)
5
6
40
VIN = 5V
20
VOUT = 1.8V
VIN = 5.0V
0.00
0
60
0
0
1
2
3
OUTPUT CURRENT (A)
4
0
1
2
3
4
OUTPUT CURRENT (A)
Die Temperature* : The temperature measurement was taken at the hottest point on the MIC22405 case and mounted on a fivesquare inch PCB (see Thermal Measurements section). Actual results will depend upon the size of the PCB, ambient temperature, and
proximity to other heat-emitting components.
June 2011
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Micrel, Inc.
MIC22405
Functional Characteristics
June 2011
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Micrel, Inc.
MIC22405
Functional Characteristics (Continued)
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Micrel, Inc.
MIC22405
Functional Characteristics (Continued)
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Micrel, Inc.
MIC22405
Functional Diagram
Figure 1. MIC22405 Functional Diagram
June 2011
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Micrel, Inc.
MIC22405
Application Information
The MIC22405 is a 4A synchronous voltage mode PWM
step down regulator IC with a programmable frequency
range from 300kHz to 4MHz. Other features include
tracking and sequencing control for controlling multiple
output power systems and power on reset (POR).
By controlling the ratio of the on-to-off time, or duty
cycle, a regulated DC output voltage is achieved. As
load or supply voltage changes, so does the duty cycle
to maintain a constant output voltage. In cases where
the input supply runs into a dropout condition, the
MIC22405 will run at 100% duty cycle.
The internal MOSFETs include a high-side P-channel
MOSFET from the input supply to the switch pin and an
N-channel MOSFET from the switch pin to ground. Since
the low-side N-channel MOSFET provides the current
during the off cycle, a very low amount of power is
dissipated during the off period.
The PWM control technique also provides fixedfrequency operation. By maintaining a constant
switching frequency, predictable fundamental and
harmonic frequencies are achieved. Other methods of
regulation, such as burst and skip modes, have
frequency spectrums that change with load that can
interfere with sensitive communication equipment.
Input Capacitor
A 22µF X5R or X7R dielectrics ceramic capacitor is
recommended on each of the PVIN pins for bypassing. A
Y5V dielectric capacitor should not be used. Aside from
losing most of their capacitance over temperature, they
also become resistive at high frequencies. This reduces
their ability to filter out high-frequency noise.
Output Capacitor
The MIC22405 was designed specifically for use with
ceramic output capacitors. The output capacitor can be
increased from 100µF to a higher value to improve
transient performance. Since the MIC22405 is in voltage
mode, the control loop relies on the inductor and output
capacitor for compensation. For this reason, do not use
excessively large output capacitors. The output capacitor
requires either an X7R or X5R dielectric. Y5V and Z5U
dielectric capacitors, aside from the undesirable effect of
their wide variation in capacitance over temperature,
become resistive at high frequencies. Using Y5V or Z5U
capacitors can cause instability in the MIC22405.
•
Size requirements
•
DC resistance (DCR)
Efficiency Considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power consumed.
⎛V
×I
Efficiency % = ⎜⎜ OUT OUT
⎝ VIN × IIN
⎞
⎟⎟ × 100
⎠
Maintaining high efficiency serves two purposes. First, it
decreases power dissipation in the power supply,
reducing the need for heat sinks and thermal design
considerations and it decreases consumption of current
for battery powered applications. Reduced current
demand from a battery increases the devices operating
time, critical in hand held devices.
There are mainly two loss terms in switching converters:
static losses and switching losses. Static losses are
simply the power losses due to VI or I2R. For example,
power is dissipated in the high side switch during the on
cycle. Power loss is equal to the high-side MOSFET
Inductor Selection
Inductor selection will be determined by the following
(not necessarily in the order of importance):
Inductance
June 2011
Rated current value
The MIC22405 is designed for use with a 0.47µH to
4.7µH inductor.
Maximum current ratings of the inductor are generally
given in two methods: permissible DC current and
saturation current. Permissible DC current can be rated
either for a 40°C temperature rise or a 10% loss in
inductance. Ensure the inductor selected can handle the
maximum operating current. When saturation current is
specified, make sure that there is enough margin so that
the peak current will not saturate the inductor. The ripple
current can add as much as 1.2A to the output current
level. The RMS rating should be chosen to be equal or
greater than the current limit of the MIC22405 to prevent
overheating in a fault condition. For best electrical
performance, the inductor should be placed very close to
the SW nodes of the IC. For this reason, the heat of the
inductor is somewhat coupled to the IC, so it offers some
level of protection if the inductor gets too hot (In such
cases IC case temperature is not a true indication of
IC dissipation). It is important to test all operating limits
before settling on the final inductor choice.
The size requirements refer to the area and height
requirements that are necessary to fit a particular
design. Please refer to the inductor dimensions on their
datasheet.
DC resistance is also important. While DCR is inversely
proportional to size, DCR increase can represent a
significant efficiency loss. Refer to the “Efficiency
Considerations” sub-section for a more detailed
description.
Component Selection
•
•
14
M9999-061511-A
Micrel, Inc.
MIC22405
selection becomes a trade-off between efficiency and
size in this case.
Alternatively, under lighter loads, the ripple current due
to the inductance becomes a significant factor. When
light load efficiencies become more critical, a larger
inductor value maybe desired. Larger inductances
reduce the peak-to-peak inductor ripple current, which
minimize losses.
RDS(ON) multiplied by the RMS switch current squared
(ISW2). During the off-cycle, the low-side N-channel
MOSFET conducts, also dissipating power. Similarly, the
inductor’s DCR and capacitor’s ESR also contribute to
the I2R losses. Device operating current also reduces
efficiency by the product of the quiescent (operating)
current and the supply voltage. The current required to
drive the gates on and off at a constant 1MHz frequency
and the switching transitions make up the switching
losses.
Figure 2 illustrates a typical efficiency curve. From 0A to
0.2A, efficiency losses are dominated by quiescent
current losses, gate drive, transition and core losses. In
this case, lower supply voltages yield greater efficiency
in that they require less current to drive the MOSFETs
and have reduced input power consumption.
Compensation
The MIC22405 has a combination of internal and
external stability compensation to simplify the circuit for
small, high efficiency designs. In such designs, voltage
mode conversion is often the optimum solution. Voltage
mode is achieved by creating an internal ramp signal
and using the output of the error amplifier to modulate
the pulse width of the switch node, thereby maintaining
output voltage regulation. With a typical gain bandwidth
of 100kHz − 200kHz, the MIC22405 is capable of
extremely fast transient response.
The MIC22405 is designed to be stable with a typical
application using a 1µH inductor and a 100µF ceramic
(X5R) output capacitor. These values can be varied
dependent upon the tradeoff between size, cost and
efficiency, keeping the LC natural frequency
⎛
⎞
1
⎜
⎟ ideally less than 26 kHz to ensure
⎜
⎟
⎝ 2× π × L×C ⎠
stability can be achieved. The minimum recommended
inductor value is 0.47µH and minimum recommended
output capacitor value is 22µF. The tradeoff between
changing these values is that with a larger inductor,
there is a reduced peak-to-peak current which yields a
greater efficiency at lighter loads. A larger output
capacitor will improve transient response by providing a
larger hold up reservoir of energy to the output.
Efficiency (VIN = 5.0V)
vs. Output Current
100
3.3V
EFFICIENCY (%)
95
90
1.8V
85
80
VIN = 5.0V
75
70
0
1
2
3
4
OUTPUT CURRENT (A)
Figure 2. Efficiency Curve
From 0.5A to 4A, efficiency loss is dominated by
MOSFET RDS(ON) and inductor DC losses. Higher input
supply voltages will increase the gate-to-source voltage
on the internal MOSFETs, thereby reducing the internal
RDS(ON). This improves efficiency by decreasing DC
losses in the device. All but the inductor losses are
inherent to the device. In which case, inductor selection
becomes increasingly critical in efficiency calculations.
As the inductors are reduced in size, the DC resistance
(DCR) can become quite significant. The DCR losses
can be calculated as follows:
LPD = IOUT2 × DCR
From that, the loss in efficiency due to inductor
resistance can be calculated as follows:
⎡ ⎛
VOUT × IOUT
Efficiency Loss = ⎢1− ⎜⎜
⎢⎣ ⎝ (VOUT × IOUT ) + L PD
⎞⎤
⎟⎥ × 100
⎟
⎠⎥⎦
Efficiency loss due to DCR is minimal at light loads and
gains significance as the load is increased. Inductor
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MIC22405
The integration of one pole-zero pair within the control
loop greatly simplifies compensation. The optimum
values for CCOMP (in series with a 20k resistor) are shown
below.
CÆ
LÈ
22µF ̶ 47µF
47µF ̶ 100µF
100µF ̶ 470µF
0* ̶ 10pF
22pF
33pF
0.47µH
†
1µH
0 ̶ 15pF
15 ̶ 22pF
33pF
2.2µH
15 ̶ 33pF
33 ̶ 47pF
100 ̶ 220pF
CF Capacitor
Frequency
56pF
4.4MHz
68pF
4MHz
82pF
3.4MHz
100pF
2.8MHz
150pF
2.1MHz
180pF
1.7MHz
220pF
1.4MHz
270pF
1.2MHz
330pF
1.1MHz
390pF
1.05MHz
470pF
1MHz
Table 2. CF vs. Frequency
†
* VOUT > 1.2V, VOUT > 1V
Table 1. Compensation Capacitor Selection
Note: Compensation values for various output voltages and
inductor values refer to table 3.
It is necessary to connect the CF capacitor between the
CF pin and signal ground.
300kHz to 800kHz Operation
The frequency range can be lowered by adding an
additional resistor (RCF) in parallel with the CF capacitor.
This reduces the amount of current used to charge the
capacitor, reducing the frequency. The following
equation can be used to for frequencies between
800kHz to 300kHz.:
Feedback
The MIC22405 provides a feedback pin to adjust the
output voltage to the desired level. This pin connects
internally to an error amplifier. The error amplifier then
compares the voltage at the feedback to the internal
0.7V reference voltage and adjusts the output voltage to
maintain regulation. The resistor divider network for a
desired VOUT is given by:
R2 =
⎛
1.0V
− R CF × C CF × ln⎜1 +
⎜
400μ0 × R CF
⎝
R CF > 2.9KΩ
R1
⎛V
⎞
⎜ OUT − 1⎟
⎜V
⎟
⎝ REF
⎠
RC Pin (Soft-Start)
The RC pin provides a trimmed 1µA current source/sink
for accurate ramp-up (soft-start). This allows the
MIC22405 to be used in systems requiring voltage
tracking or ratio-metric voltage tracking at startup.
There are two ways of using the RC pin:
1. Externally driven from a voltage source
2. Externally attached capacitor sets output rampup/down rate
In the first case, driving RC with a voltage from 0V to
VREF will program the output voltage between 0 and
100% of the nominal set voltage as shown in figure 3.
In the second case, the external capacitor sets the rampup and ramp-down time of the output voltage. The time
is given by
where VREF is 0.7V and VOUT is the desired output
voltage. A 10kΩ or lower resistor value from the output
to the feedback (R1) is recommended since large
feedback resistor values increase the impedance at the
feedback pin, making the feedback node more
susceptible to noise pick-up. A small capacitor (50pF –
100pF) across the lower resistor can reduce noise pickup by providing a low impedance path to ground.
Enable/Delay (EN/DLY) Pin
Enable/Delay (EN/DLY) sources 1µA out of the IC to
allow a startup delay to be implemented. The delay time
is simply the time it takes 1µA to charge CEN/DLY to
1.25V. Therefore:
t EN/DLY =
1.24 × C EN/DLY
1× 10 − 6
t RAMP =
0.7 × C RC
1× 10 − 6
is the time from 0 to 100% nominal output
CF Capacitor
Adding a capacitor to this pin can adjust switching
frequency from 800kHz to 4MHz. CF sources 400µA out
of the IC to charge the CF capacitor to set up the
switching frequency. The switch period is simply the time
it takes 400µA to charge CF to 1.0V. Therefore:
June 2011
⎞
⎟=t
⎟
⎠
Where tRAMP
voltage.
During start-up, a light load condition (IOUT < 1.25A) can
lead to negative inductor current. Under these
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MIC22405
conditions, the maximum ramp-up time should not
exceed the critical ramp-up time period to keep regulator
in continuous mode operation when VFB reaches 90% of
reference voltage.
Beyond the critical ramp-up time, the regulator is in
discontinuous mode which leads to prolonged N-channel
MOSFET conduction, which in turn causes negative
inductor current.
The maximum CRC value is calculated as follows.
CRC <
2.86 • COUT • L • FSW • 10
1
MOSFET will turn on until the ramp control voltage (VRC)
is above the reference voltage (VREF). Then, the highside MOSFET starts switching, forcing the output to
follow the VRC ramp. Once the feedback voltage is
above 90 percent of the reference voltage, the low-side
MOSFET will begin switching.
6
VOUT
VIN
Pre-Bias Start-Up
The MIC22405 is designed for safe start-up into a prebiased output. This prevents large negative inductor
currents and excessive output voltage oscillations. The
MIC22405 starts with the low-side MOSFET turned off,
preventing reverse inductor current flow. The
synchronous MOSFET stays off until the Power Good
(PG) goes high after the VFB is above 90 percent of VREF.
A pre-bias condition can occur if the input is turned off
then immediately turned back on before the output
capacitor is discharged to ground. It is also possible that
the output of the MIC22405 could be pulled up or prebiased through parasitic conduction paths from one
supply rail to another in multiple voltage (VOUT) level
ICs such as a FPGA.
Figure 3 shows a normal start-up waveform. A 1µA
current source charges the soft-start capacitor CRC. The
CRC capacitor forces the VRC voltage to come up slowly
(VRC trace), thereby providing a soft-start ramp. This
ramp is used to control the internal reference (VREF).
The error amplifier forces the output voltage to follow the
VREF ramp from zero to the final value.
Figure 4. EN Turn-On at 1V Pre-Bias
When the MIC22405 is turned off, the low-side MOSFET
will be disabled and the output voltage will decay to zero.
During this time, the ramp control voltage (VRC) will still
control the output voltage fall-time with the high-side
MOSFET if the output voltage falls faster than the VRC
voltage. Figure 5 shows this operating condition. Here a
4A load pulls the output down fast enough to force the
high-side MOSFET on (VSW trace).
Figure 5. EN Turn-OFF − 7A Load
If the output voltage falls slower than the VRC voltage,
then the both MOSFETs will be off and the output will
decay to zero as shown in the VOUT trace in Figure 6 with
both MOSFETs off, any resistive load connected to the
output will help pull down the output voltage. This will
occur at a rate determined by the resistance of the load
and the output capacitance.
Figure 3. EN Turn-On Time − Normal Start-Up
If the output is pre-biased to a voltage above the
expected value, as shown in Figure 4, then neither
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MIC22405
Thermal Considerations
The MIC22405 is packaged in a MLF® 3mm x 4mm – a
package that has excellent thermal-performance
equaling that of the larger TSSOP packages. This
maximizes heat transfer from the junction to the exposed
pad (ePad) which connects to the ground plane. The
size of the ground plane attached to the exposed pad
determines the overall thermal resistance from the
junction to the ambient air surrounding the printed circuit
board. The junction temperature for a given ambient
temperature can be calculated using:
TJ = TAMB + PDISS × RθJA
Figure 6. EN Turn-Off − 200mA Load
where:
Current Limit
The MIC22405 uses a two-stage technique to protect
against overload. The first stage is to limit the current in
the P-channel switch; the second is over temperature
shutdown.
Current is limited by measuring the current through the
high-side MOSFET during its power stroke and
immediately switching off the driver when the preset limit
is exceeded.
The circuit in Figure 7 describes the operation of the
current limit circuit. Since the actual RDSON of the Pchannel MOSFET varies from part to part, and with
changes in temperature and with input voltage, simple IR
voltage detection is not employed. Instead, a smaller
copy of the Power MOSFET (Reference FET) is fed with
a constant current which is a directly proportional to the
factory set current limit. This sets the current limit as a
current ratio and thus, is not dependant upon the RDSON
value. Current limit is set to nominal value. Variations in
the scale factor K between the power PFET and the
reference PFET used to generate the limit threshold
account for a relatively small inaccuracy.
•
PDISS is the power dissipated within the MLF®
package and is at 4A load. RθJA is a combination of
junction-to-case thermal resistance (RθJC) and
Case-to-Ambient thermal resistance (RθCA), since
thermal resistance of the solder connection from the
ePAD to the PCB is negligible; RθCA is the thermal
resistance of the ground plane-to-ambient, so RθJA =
RθJC + RθCA.
•
TAMB is the operating ambient temperature.
Example:
The Evaluation board has two copper planes
contributing to an RθJA of approximately 55°C/W. The
worst case RθJC of the MLF 3mmx4mm is 25oC/W.
RθJA = RθJC + RθCA
RθJA = 25 + 30 = 55oC/W
To calculate the junction temperature for a 50°C
ambient:
TJ = TAMB+PDISS . RθJA
TJ = 50 + (0.89 x 55)
TJ = 98.95°C
This is below the maximum of 125°C.
Figure 7. Current-Limit Detail
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MIC22405
Window Sequencing:
Thermal Measurements
Measuring the IC’s case temperature is recommended to
ensure it is within its operating limits. Although this might
seem like a very elementary task, it is easy to get
erroneous results. The most common mistake is to use
the standard thermal couple that comes with a thermal
meter. This thermal couple wire gauge is large, typically
22 gauge, and behaves like a heat-sink, resulting in a
lower case measurement.
Two better methods of temperature measurement are
using a smaller thermal couple wire or an infrared
thermometer. If a thermal couple wire is used, it must be
constructed of 36 gauge wire or higher then (smaller
wire size) to minimize the wire heat-sinking effect. In
addition, the thermal couple tip must be covered in either
thermal grease or thermal glue to make sure that the
thermal couple junction is making good contact with the
case of the IC. Omega brand thermal couple (5SC-TT-K36-36) is adequate for most applications.
Whenever possible, an infrared thermometer is
recommended. The measurement spot size of most
infrared thermometers is too large for an accurate
reading on a small form factor ICs. However, an IR
thermometer from Optris has a 1mm spot size, which
makes it a good choice for measuring the hottest point
on the case. An optional stand makes it easy to hold the
beam on the IC for long periods of time.
Sequencing and Tracking
There are four variations which are easily implemented
using the MIC22405. The two sequencing variations are
Delayed and Windowed. The two tracking variants are
Normal and Ratio Metric. The following diagrams
illustrate methods for connecting two MIC22405’s to
achieve these requirements.
Time (4.0ms/div)
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MIC22405
Normal Tracking:
Delayed Sequencing:
Time (4.0ms/div)
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Time (4.0ms/div)
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MIC22405
Ratio Metric Tracking:
Time (4.0ms/div)
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MIC22405
VIN = 5V
VOUT
L
COUT
CCOMP
RCOMP
CFF
RFF
CFB
RFB
4.2V
1.5µH
2 x 47µF
100pF
20k Ω
1nF
4.7k Ω
100pF
953 Ω
Table 3. Compensation Selection
Figure 8. Schematic Reference
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Micrel, Inc.
MIC22405
Inductor
PCB Layout Guidelines
Warning!!! To minimize EMI and output noise, follow
these layout recommendations.
PCB Layout is critical to achieve reliable, stable and
efficient performance. A ground plane is required to
control EMI and minimize the inductance in power,
signal and return paths.
The following guidelines should be followed to insure
proper operation of the MIC22405 converter:
•
Keep the inductor connection to the switch node
(SW) short.
•
Do not route any digital lines underneath or close to
the inductor.
•
Keep the switch node (SW) away from the feedback
(FB) pin.
•
To minimize noise, place a ground plane underneath
the inductor.
•
The inductor can be placed on the opposite side of
the PCB with respect to the IC. It does not matter
whether the IC or inductor is on the top or bottom as
long as there is enough air flow to keep the power
components within their temperature limits. The
input and output capacitors must be placed on the
same side of the board as the IC.
IC
•
The 2.2µF ceramic capacitor, which is connected to
the SVIN pin, must be located right at the IC. The
SVIN pin is very noise sensitive and placement of
the capacitor is very critical. Use wide traces to
connect to the SVIN and SGND pins.
•
The signal ground pin (SGND) must be connected
directly to the ground planes. Do not route the
SGND pin to the PGND Pad on the top layer.
•
Place the IC close to the point of load (POL).
•
Use fat traces to route the input and output power
lines.
•
Signal and power grounds should be kept separate
and connected at only one location.
Output Capacitor
Input Capacitor
•
A 22µF X5R or X7R dielectrics ceramic capacitor is
recommended on each of the PVIN pins for
bypassing.
•
Place the input capacitors on the same side of the
board and as close to the IC as possible.
•
Keep both the PVIN pin and PGND connections
short.
•
Place several vias to the ground plane close to the
input capacitor ground terminal.
•
Use either X7R or X5R dielectric input capacitors.
Do not use Y5V or Z5U type capacitors.
•
Do not replace the ceramic input capacitor with any
other type of capacitor. Any type of capacitor can be
placed in parallel with the input capacitor.
•
If a Tantalum input capacitor is placed in parallel
with the input capacitor, it must be recommended for
switching regulator applications and the operating
voltage must be derated by 50%.
•
In “Hot-Plug” applications, a Tantalum or Electrolytic
bypass capacitor must be used to limit the overvoltage spike seen on the input supply with power is
suddenly applied.
June 2011
•
Use a wide trace to connect the output capacitor
ground terminal to the input capacitor ground
terminal.
•
Phase margin will change as the output capacitor
value and ESR changes. Contact the factory if the
output capacitor is different from what is shown in
the BOM.
•
The feedback divider network must be place close to
the IC with the bottom of R2 connected to SGND.
•
The feedback trace should be separate from the
power trace and connected as close as possible to
the output capacitor. Sensing a long high-current
load trace can degrade the DC load regulation.
RC Snubber
•
23
Place the RC snubber on either side of the board
and as close to the SW pin as possible.
M9999-061511-A
Micrel, Inc.
MIC22405
Evaluation Board Schematic
Bill of Materials
Item
C1, C2
Part Number
AVX
C2012X5R0J226M
TDK(2)
C4, C12
GRM188R60J225M
Murata(3)
C6
TDK
AVX
C8
June 2011
Capacitor, 1nF, 10V, COG, Size 0603
2
Murata(3)
06035C471KAT2A
AVX(1)
06035A390JAT2A
1
Capacitor, 1nF, 50V, X7R, Size 0603
(1)
TDK(2)
GRM188R71H391JA01
2.2µF/6.3V, Ceramic Capacitor, X5R, Size 0603
(2)
C1608X7RH471K
C1608COG1H390J
2
(1)
Murata(3)
06035C102KAT2A
GRM188R71H390JA01
C7
TDK
C1608C0G1H102J
GRM188R71H471KA01D
Capacitor, 22µF, 6.3V, X5R, Size 0805
Murata
AVX(2)
GRM188R71H102KA01D
Qty.
(3)
06036D225MAT2A
C1608X5R0J225M
Description
(1)
08056D226MAT
GRM21BR60J226ME39L
C3
Manufacturer
Capacitor, 470pF, 50V, X7R, Size 0603
1
Capacitor, 39pF, 50V, Size 0603
1
Capacitor, 390pF, 50V, Size 0603
1
Murata(3)
TDK(2)
(1)
AVX
Murata(3)
1608COG1H391J
TDK(2)
06035A391JAT2A
(1)
AVX
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M9999-061511-A
Micrel, Inc.
MIC22405
Bill of Materials (Continued)
Item
Part Number
GRM188R71H101JA01
C9
Cin
L1
06035A101JT2A
AVX(1)
R1
12066D476MAT2A
(1)
AVX
B41125A3477M
Epcos
CRCW06031101FKEYE3
R2
CRCW06036980FKEYE3
1
Capacitor, 47µF, 6.3V, X5R, Size 1206
2
(3)
TDK(2)
SPM6530T-1R0M120 ( 7x6.5x3mm )
Capacitor, 100pF, 50V, Size 0603
Murata
C3216X5R0J476M
CDRH8D28NP-1R0NC ( 8x6x3mm )
Qty.
Murata
TDK(2)
FP3-1R0-R( 7.2x6.7x3mm )
Description
(3)
C1608COG1H101J
GRM31CR60J476ME19
C10, C11
Manufacturer
470µF, 10V, Electrolytic, 8x10-case
(5)
Inductor, 1µH, 6.26A
1
(6)
Inductor, 1µH, 8A
1
Inductor, 1µH, 12A
1
(4)
Resistor, 1.1k, 1%, Size 0603
1
(4)
Resistor, 698, 1%, Size 0603
1
(4)
Cooper
Sumida
TDK(2)
Vishay
Vishay
R3
CRCW06032002FKEYE3
Vishay
Resistor, 20k, 1%, Size 0603
1
R4
CRCW06034752FKEYE3
Vishay(4)
Resistor, 47.5k, 1%, Size 0603
1
(4)
Resistor, 100k, 1%, Size 0603
1
(4)
R5
(Open) CRCW06031003FKEYE3
Vishay
R6
CRCW06032R20FKEA
Vishay
Resistor, 2.2Ω, 1%, Size 0603
1
R7
CRCW060349R9FKEA
Vishay(4)
Resistor, 49.9Ω, 1%, Size 0603
1
(4)
Open
1
(7)
Integrated 4A Synchronous Buck Regulator
1
Q1
2N7002E
U1
MIC22405YML
Vishay
Micrel
Notes:
1.
AVX: www.avx.com
2.
TDK: www.tdk.com
3.
Murata: www.murata.com
4.
Vishay: www.vishay.com
5.
Cooper Bussmann: www.cooperet.com
6.
Sumida: www.sumida.com
7.
Micrel, Inc.: www.micrel.com
June 2011
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MIC22405
PCB Layout Recommendations
MIC22405 Evaluation Board Top Layer
MIC22405 Evaluation Board Top Silk
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MIC22405
PCB Layout Recommendations (Continued)
MIC22405 Evaluation Board Mid-Layer 1 (Ground Plane)
MIC22405 Evaluation Board Mid-Layer 2
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MIC22405
PCB Layout Recommendations (Continued)
MIC22405 Evaluation Board Bottom Layer
MIC22405 Evaluation Board Bottom Silk
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MIC22405
Package Information
20-Pin 3mm × 4mm MLF® (ML)
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MIC22405
Recommended Landing Pattern
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This information
is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and
descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted
by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel
disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular
purpose, merchantability, or infringement of any patent, copyright or other intellectual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the
body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or
sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for
any damages resulting from such use or sale.
© 2010 Micrel, Incorporated.
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