MICREL MIC22400YML

MIC22400
4A Integrated Switch Synchronous
Buck Regulator with Frequency
Programmable up to 4MHz
General Description
The Micrel MIC22400 is a high-efficiency, 4A integrated
switch synchronous buck (step-down) regulator. The
MIC22400 is optimized for highest efficiency, achieving
over 90% efficiency while still switching at 1MHz over a
broad load range. The ultra-high-speed control loop keeps
the output voltage within regulation even under extreme
transient load swings commonly found in FPGAs and lowvoltage ASICs. The output voltage can be adjusted down
to 0.7V to address all low-voltage power needs. The
MIC22400 gives a full range of sequencing and tracking
options. The EN/DLY pin combined with the Power-OnReset (POR) pin allows multiple outputs to be sequenced
in any way on turn-on and turn-off. The Ramp Control™
(RC) pin allows the device to be connected to another
MIC22400 family of products to keep the output voltages
within a certain ΔV on start-up.
®
The MIC22400 is available in a 20-pin 3mm x 4mm MLF
and thermally-enhanced 20-pin ePad TSSOP 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.
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Input voltage range: 2.6V to 5.5V
Output voltage adjustable down to 0.7V
Output load current up to 4A
Full sequencing and tracking ability
Power-On-Reset (POR)
Efficiency > 90% across a broad load range
Programmable frequency 300kHz to 4MHz
Easy Ramp Control™ (RC) compensation
Ultra-fast transient response
100% maximum duty cycle
Fully-integrated MOSFET switches
Micropower shutdown
Thermal-shutdown and current-limit protection
20-pin 3mm x 4mm MLF®
20-pin ePad TSSOP
–40°C to +125°C junction temperature range
Applications
•
•
•
•
•
•
High power density point-of-load conversion
Servers and routers
DVD recorders
Computing peripherals
Base stations
FPGAs, DSP and low-voltage ASIC power
Typical Application
MIC22400 4A Synchronous Buck Regulator
Sequencing & Tracking
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
June 2011
M9999-061511-F
Micrel, Inc.
MIC22400
Ordering Information
Part Number
Voltage
Junction Temperature Range
Package
Lead Finish
®
MIC22400YML
Adjustable
–40° to +125°C
20-Pin 3x4 MLF *
Pb-Free
MIC22400YTSE**
Adjustable
–40° to +125°C
20-Pin e-TSSOP
Pb-Free
Notes:
* MLF is a Green RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
** Contact Micrel Marketing for YTSE availability.
Pin Configuration
20-Pin 3mm x 4mm MLF® (ML)
20-Pin e-TSSOP (TS)
Pin Description
Pin Number
MLF-20
Pin Number
e-TSSOP-20
Pin Name
1
4
POR
2
5
CF
Adjustable frequency with external capacitor. Refer to table on page 12.
3, 5, 9
7, 12, 19
NC
Not connected internally.
4
6
COMP
Compensation pin (Input): Place a RC to GND to compensate the device, see
applications section.
6
8
FB
Feedback (Input): Input to the error amplifier, connect to the external resistor
divider network to set the output voltage.
7
9
SGND
Signal Ground (Signal): Ground
8
10
SVIN
Signal Power Supply Voltage (Input): Requires bypass capacitor to GND.
10, 17
11, 20
PVIN
Power Supply Voltage (Input): Requires bypass capacitor to GND.
11, 16
13, 18
PGND
Power Ground (Signal): Ground
12, 13, 14, 15
14, 15, 16, 17
SW
June 2011
Description
Power-On-Reset (Output): Open-drain output device indicates when the output is
out of regulation and is active after the delay set by the DELAY pin.
Switch (Output): Internal power MOSFET output switches.
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MIC22400
Pin Description (Continued)
Pin Number
MLF-20
Pin Number
e-TSSOP-20
Pin Name
Description
18
1
EN/DLY
Enable (Input): When this pin is pulled higher than the enable threshold, the part
will start up. Below this voltage the device is in its low quiescent current mode.
The pin has a 1µA current source charging it to VDD. By adding a capacitor to this
pin a delay may easily be generated. The enable function will not operate with an
input voltage lower than the min specified.
19
2
DELAY
Delay (Input): Capacitor-to-ground sets internal delay timer. Timer delays POR
output at turn-on and ramp down at turn-off.
20
3
RC
Ramp Control: Capacitor to ground from this pin determines slew rate of output
voltage during start-up. This can be used for tracking capability as well as soft
start.
EP
EP
GND
June 2011
Exposed Pad (Power): Must make a full connection to a GND plane.
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Micrel, Inc.
MIC22400
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VIN) .........................................................6V
Output Switch Voltage (VSW) ............................................6V
Output Switch Current (ISW)..............................................6A
Logic Input Voltage (VEN, VLQ)........................... VIN to –0.3V
Lead Temperature...................................................... 260°C
Storage Temperature (Ts) .........................–65°C to +150°C
ESD Rating.................................................................Note 3
Supply Voltage (VIN)......................................... 2.6V to 5.5V
Junction Temperature (TJ) ..................–40°C ≤ TJ ≤ +125°C
Thermal Resistance
3x4 MLF-20 (θJA) ...............................................45°C/W
e-TSSOP-20 (θJA) ...........................................32.2°C/W
Electrical Characteristics(4)
TA = 25°C with VIN = VEN = 3.3V; VOUT = 1.2V, CF = 400pF, unless otherwise specified. Bold values indicate –40°C< TJ < +125°C.
Parameter
Supply Voltage Range
Undervoltage Lockout Threshold
UVLO Hysteresis
Quiescent Current, PWM Mode
Shutdown Current
[Adjustable] Feedback Voltage
Condition
Min.
2.6
2.4
(turn-on)
VEN ≥1.34V; VFB = 0.9V (not switching)
VEN = 0V
± 1%
± 2% (over temperature)
Oscillator Frequency
FB Pin Input Current
Current Limit
Output Voltage Line Regulation
Output Voltage Load Regulation
Maximum Duty Cycle
Switch ON-Resistance PFET
Switch ON-Resistance NFET
EN/DLY Threshold Voltage
EN/DLY Source Current
VFB = 0.5V
VOUT 1.2V; VIN = 2.6 to 5.5V, ILOAD= 100mA
100mA < ILOAD < 4000mA, VIN = 3.3V
VFB ≤ 0.5V
ISW = 1000mA; VFB=0.5V
ISW = 1000mA; VFB=0.9V
VIN = 2.6 to VIN = 5.5V
RC Pin IRAMP
Ramp Control Current
POR IPOR(LEAK)
VPORH = 5.5V; POR = High
POR VPOR(LO)
Output Logic-Low Voltage (undervoltage condition),
IPOR = 5mA
POR VPOR
Threshold, % of VOUT below nominal
Hysteresis
Over-Temperature Shutdown
Over-Temperature Shutdown
Hysteresis
0.693
0.686
0.8
4
Typ.
2.5
280
1.3
5
0.7
1
1
7
0.2
0.2
Max.
Units
5.5
2.6
V
V
mV
mA
µA
V
V
MHz
nA
A
%
%
%
Ω
Ω
V
µA
2.0
10
0.707
0.714
1.2
10
100
1.14
0.7
0.060
0.035
1.24
1
1.34
1.3
0.7
1
1.3
µA
1
2
µA
µA
135
7.5
10
mV
12.5
%
2.7
%
150
°C
10
°C
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended.
4. Specification for packaged product only.
June 2011
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MIC22400
Typical Characteristics
10
Shutdown Current
vs. Input Voltage
10
Shutdown Current
vs. Temperature
2.0
8
8
1.6
6
6
1.2
4
0.8
2
0.4
4
TA=25°C
2
0
2.5
2.0
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
5.5
Quiescent Current
vs. Temperature
1.6
VIN = 3.3V
0
0
2.5
TEMPERATURE (°C)
0.710
Reference Voltage
vs. Input Voltage
0.710
0.705
Quiescent Current
vs. Input Voltage
No Switching
FB = 0.9V
25°C
3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
Reference Voltage
vs. Temperature
0.705
1.2
0.700
0.8
0.4
0
No Switching
FB = 0.9V
VIN = 3.3V
1.30
1.26
1.22
1.18
1.14
1.10
65
VIN = 3.3V
0.690
2.5
8
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
Enable Hysterisis
vs. Temperature
0.690
1060
6
1020
5
1000
4
980
3
960
2
940
1
VIN = 3.3V
0
TEMPERATURE (°C)
P-Channel RDS ON
vs. Temperature
N-Channel RDS ON
vs. Temperature
40
38
61
36
59
34
57
32
VIN = 3.3V
TEMPERATURE (°C)
1040
TEMPERATURE (°C)
55
5.5
7
63
Frequency
vs. Temperature
VIN = 3.3V
CF = 390pF
920
900
TEMPERATURE (°C)
30
TEMPERATURE (°C)
June 2011
0.695
0.695
TEMPERATURE (°C)
Enable Voltage
vs. Temperature
0.700
TA=25°C
TEMPERATURE (°C)
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Micrel, Inc.
MIC22400
Typical Characteristics (Continued)
Efficiency V O = 3.3V
Efficiency V O = 1.8V
Efficiency V O = 1.2V
100
100
95
95
90
90
85
85
80
80
80
75
75
75
70
70
70
65
65
65
60
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
OUTPUT CURRENT (A)
60
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
OUTPUT CURRENT (A)
VIN = 5V
60
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
OUTPUT CURRENT (A)
V IN = 5.0V, V OUT = 1.2V
60
150
Phase @ 4A
20
0
-20
40
0
VIN - 5V
85
-50
Phase @ 4A
-20
-100
-40
-60
1
June 2011
-150
10
100
FREQUENCY (kHz)
-200
1,000
150
200
60
40
Phase @ 4A
100
50
Gain @ 4A
VIN - 5V
VIN = 3.3V, V OUT = 1.8V
200
20
0
VIN - 3.3V
90
60
100
50
Gain @ 4A
95
V IN = 3.3V, V OUT = 1.2V
200
40
100
VIN - 3.3V
0
-50
100
20
50
0
0
-20
Gain @ 4A
-60
1
-150
10
100
FREQUENCY (kHz)
6
-200
1,000
-50
-100
-100
-40
150
-40
-60
1
-150
10
100
FREQUENCY (kHz)
-200
1,000
M9999-061511-F
Micrel, Inc.
MIC22400
Functional Characteristics
June 2011
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Micrel, Inc.
MIC22400
Functional Characteristics (Continued)
June 2011
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Micrel, Inc.
MIC22400
Figure 1. Tracking Circuit and Waveform
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MIC22400
Functional Diagram
Figure 2. MIC22400 Block Diagram
June 2011
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MIC22400
Functional Description
PVIN, SVIN
PVIN is the input supply to the internal 60mΩ P-Channel
Power MOSFET. This should be connected externally to
the SVIN pin. The supply voltage range is from 2.6V to
5.5V. A 22µF ceramic is recommended for bypassing
each PVIN supply.
FB
The feedback pin provides the control path to control the
output. A resistor divider connecting the feedback to the
output is used to adjust the desired output voltage. Refer
to the “Feedback” section in Applications Information for
more detail.
EN/DLY
This pin is internally fed with a 1µA current source to
VIN. 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.
POR
This is an open drain output. A 47k resistor can be used
for a pull up to this pin. POR is asserted high when
output voltage reaches 90% of nominal set voltage and
after the delay set by CDELAY. POR is asserted low
without delay when enable is set low or when the output
goes below the -10% threshold. For a Power-on-Reset
(POR) function, the delay can be set to a minimum. This
can be done by removing the DELAY pin capacitor.
RC
RC allows the slew rate of the output voltage to be
programmed by the addition of a capacitor from RC to
ground. RC is internally fed with a 1µA current source
and VOUT slew rate is proportional to the capacitor and
the 1µA source.
SW
This is the connection to the drain of the internal PChannel 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.
DELAY
Adding a capacitor to this pin allows the delay of the
POR signal.
When VOUT reaches 90% of its nominal voltage, the
DELAY pin current source (1µA) starts to charge the
external capacitor. At 1.24V, POR is asserted high.
CF
Adding a
frequency
additional
range can
1).
COMP
The MIC22400 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 will add
the necessary pole and zero for voltage mode loop
stability using low value, low ESR ceramic capacitors.
June 2011
capacitor to this pin can adjust switching
from 800kHz to 4MHz. By adding an
resistor from CF to ground, the frequency
be extended down to 300KHz (refer to Table
SGND
Internal signal ground for all low power sections.
PGND
Internal ground connection to the source of the internal
N-Channel MOSFETs.
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MIC22400
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. 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 can represent a significant
efficiency loss. Refer to the “Efficiency Considerations”
section for a more detailed description.
Application Information
The MIC22400 is a 4A synchronous step-down regulator
IC with an adjustable switching frequency from 800kHz
to 4MHz, voltage-mode PWM control scheme. The other
features include tracking and sequencing control for
controlling multiple output power systems, power on
reset.
Component selection
Input Capacitor
A minimum 22µF ceramic is recommended on each of
the PVIN pins for bypassing. X5R or X7R dielectrics are
recommended for the input capacitor. Do not use Y5V
dielectrics. They lose most of their capacitance over
temperature and become resistive at high frequencies.
This reduces their ability to filter out high frequency
noise.
EN/DLY Capacitor
EN/DLY pin 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:
Output Capacitor
The MIC22400 was designed specifically for the use of
ceramic output capacitors. A 100µF can be increased to
improve transient performance. Since the MIC22400 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 MIC22400.
TEN/DLY =
Inductance
•
Rated current value
•
Size requirements
•
DC resistance (DCR)
CF Capacitor
56pF
68pF
82pF
100pF
150pF
180pF
220pF
270pF
330pF
390pF
470pF
The MIC22400 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 that
the peak current will not saturate the inductor. The ripple
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 MIC22400 to prevent overheating
in a fault condition.
June 2011
1.10 −6
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:
Inductor Selection
Inductor selection will be determined by the following
(not necessarily in the order of importance):
•
1.24 ⋅ C EN/DLY
Frequency
4.4MHz
4MHz
3.4MHz
2.8MHz
2.1MHz
1.7MHz
1.4MHz
1.2MHz
1.1MHz
1.05MHz
1MHz
Table 1. CF vs. Frequency
It is necessary to connect the CF capacitor between the
CF pin and power ground.
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Micrel, Inc.
MIC22400
300kHz to 800kHz Operation
Additionally, 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.:
⎛
1.0V
− RCF × CCF × ln⎜⎜1 +
μ
400
A × RCF
⎝
RCF > 2.9KΩ
⎞
⎟=t
⎟
⎠
Efficiency Considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power consumed:
⎛V
×I
Efficiency % = ⎜⎜ OUT OUT
V
IN × I IN
⎝
Figure 3. Efficiency Curve
The region, 0.2A 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, reducing the internal RDS(ON).
This improves efficiency by reducing 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:
⎞
⎟⎟ × 100
⎠
Maintaining high efficiency serves two purposes. 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 draw
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
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 in the frequency range from
800kHz to 4MHz and the switching transitions make up
the switching losses.
Figure 3 shows an efficiency curve. The portion, from 0A
to 0.2A, efficiency losses are dominated by quiescent
current losses, gate drive and transition 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.
June 2011
LPD = IOUT2 × DCR
From that, the loss in efficiency due to inductor
resistance can be calculated as follows:
Efficiency Loss =
⎡ ⎛
VOUT ⋅ I OUT
⎢1 − ⎜⎜
(
V
⎣⎢ ⎝ OUT ⋅ I OUT ) + LPD
⎞⎤
⎟⎥ × 100
⎟
⎠⎦⎥
Efficiency loss due to DCR is minimal at light loads and
gains significance as the load is increased. Inductor
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 may be desired. Larger inductances
reduce the peak-to-peak inductor ripple current, which
minimize losses. Figure 4 illustrates the effects of
inductance value at light load.
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MIC22400
94
92
Efficiency
vs. Inductance
Note: For compensation values for various output
voltages and inductor values refer to Table 4.
4.7µH
90
Feedback
The MIC22400 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:
88
86
84
1µH
82
80
78
76
0
VIN = 3.3V
0.2 0.4 0.6 0.8 1.0 1.2
OUTPUT CURRENT (A)
Figure 4. Efficiency vs. Inductance
R2 =
Compensation
The MIC22400 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 1MHz 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 100 − 200kHz, the MIC22400 is capable of
extremely fast transient responses.
The MIC22400 is designed to be stable with a typical
application using a 1µH inductor and a 47µF ceramic
(X5R) output capacitor. These values can be varied
dependant 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.
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
in Table 2.
CÆ
22-47µF
LÈ
47µF100µF
0*-10pF
22pF
33pF
1µH
0†-15pF
15-22pF
33pF
15-33pF
33-47pF
100-220pF
2.2µH
⎞
⎛ VOUT
⎜⎜
− 1⎟⎟
⎠
⎝ VREF
where VREF is 0.7V and VOUT is the desired output
voltage. A 10kΩ or lower resistor value from the output
to the feedback 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 pick-up by providing
a low impedance path to ground.
PWM Operation
The MIC22400 is a voltage mode, pulse width
modulation (PWM) controller. By controlling the ratio of
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 MIC22400 will run at 100% duty
cycle.
The MIC22400 provides constant switching from 800kHz
to 4MHz with synchronous internal MOSFETs. The
internal MOSFETs include a 60mΩ high-side P-Channel
MOSFET from the input supply to the switch pin and a
30mΩ N-Channel MOSFET from the switch pin-toground. Since the low-side N-Channel MOSFET
provides the current during the off cycle, a freewheeling
Schottky diode from the switch node-to-ground is not
required.
PWM control provides fixed-frequency 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.
100µF470µF
0.47µH
R1
†
* VOUT > 1.2V, VOUT > 1V
Table 2. Compensation Capacitor Selection
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MIC22400
is given by TRAMP =
0.7 ⋅ C RC
where TRAMP is the time
1.10 −6
from 0 to 100% nominal output voltage.
Sequencing and Tracking
The MIC22400 provides additional pins to provide
up/down sequencing and tracking capability for
connecting multiple voltage regulators together.
EN/DLY Pin
The EN/DLY pin contains a trimmed, 1µA current source
which can be used with a capacitor to implement a fixed
desired delay in some sequenced power systems. The
threshold level for power on is 1.24V with a hysteresis of
20mV.
Sequencing and Tracking Examples
There are four distinct variations which are easily
implemented using the MIC22400. The two sequencing
variations are Windowed and Delayed. The two tracking
variants are Normal and Ratio Metric. The following
diagrams illustrate methods for connecting two
MIC22400’s to achieve these requirements:
Sequencing:
DELAY Pin
The DELAY pin also has a 1µA trimmed current source
and a 1µA current sink which acts with an external
capacitor to delay the operation of the Power On Reset
(POR) output. This can be used also in sequencing
outputs in a sequenced system, but with the addition of a
conditional delay between supplies; allowing a first up,
last down power sequence.
After EN/DLY is driven high, VOUT will start to rise (rate
determined by RC capacitor). As the FB voltage goes
above 90% of its nominal set voltage, DELAY begins to
rise as the 1µA source charges the external capacitor.
When the threshold of 1.24V is crossed, POR is
asserted high and DELAY continues to charge to a
voltage VDD. When FB falls below 90% of nominal, POR
is asserted low immediately. However, if EN/DLY is
driven low, POR will fall immediately to the low state and
DELAY will begin to fall as the external capacitor is
discharged by the 1µA current sink. When the threshold
of VDD-1.24V is crossed, VOUT will begin to fall at a rate
determined by the RC capacitor. As the voltage change
in both cases is 1.24V, both rising and falling delays are
1.24 ⋅ C DELAY
.
matched at TPOR =
1.10 −6
RC Pin
The RC pin provides a trimmed 1µA current source/sink
similar to the DELAY pin for accurate ramp up (soft start)
and ramp down control. This allows the MIC22400 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 ramp
up/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.
In the second case, the external capacitor sets the ramp
up and ramp down time of the output voltage. The time
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MIC22400
Normal Tracking:
June 2011
Ratio Metric Tracking:
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Micrel, Inc.
MIC22400
An alternative method here shows an example of a VDDQ
& VTT solution for a DDR memory power supply. Note
that POR is taken from VO1 as POR2 will not go high.
This is because POR is set high when FB > 0.9⋅VREF. In
this example, FB2 is regulated to ½⋅VREF.
Current Limit
The MIC22400 is protected against overload in two
stages. The first 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.
Figure 5 describes the operation of the current limit
circuit. Since the actual RDSON of the P-Channel
MOSFET varies part-to-part, over 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 6A nominal. 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.
Figure 5. Current-Limit Detail
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MIC22400
•
Thermal Considerations
The MIC22400 is packaged in the 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:
TAMB is the Operating Ambient temperature.
Example:
To calculate the junction temperature for a 50°C
ambient:
TJ = TAMB+PDISS . RθJA
TJ = 50 + 0.894 x 45
TJ = 90.2°C
This is below the maximum of 125°C.
TJ = TAMB + PDISS · RθJA
where:
•
PDISS is the power dissipated within the MLF®
package and is typically 0.89W at 3A load. This has
been calculated for a 1µH inductor and details can
be found in Table 3 for reference.
•
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.
VINÆ
VOUT
@3AÈ
3
3.5
4
4.5
5
1
0.732
0.689
0.672
0.668
0.670
1.2
0.741
0.691
0.668
0.662
0.665
1.8
0.825
0.764
0.732
0.720
0.720
2.5
0.894
0.813
0.776
0.762
0.765
3.3
–
0.817
0.816
0.801
0.800
Table 3. Power Dissipation (W) for 4A Output
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MIC22400
VIN = 5V
VOUT
L
COUT
CCOMP
RCOMP
CFF
RFF
CFB
RFB
4.2V
1.5µH
2 x 47µF
100pF
20kΩ
1nF
4.7kΩ
100pF
953Ω
Table 4. Compensation Selection
Figure 6. Table 4 Schematic Reference
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MIC22400
Evaluation Board Schematic
Figure 7. MIC22400YML Evaluation Board Schematic
(R7 is for testing purposes)
Bill of Materials
Item
C1, C2
Part Number
AVX
C2012X5R0J226M
TDK(2)
06036D225TAAT2A
GRM188R7160J225M
C1608X5R0J225M
GRM188R71H102KA01D
C4, C5, C12
C1608C0G1H102J
06035C102KAT2A
GRM188R71H103KA01D
C6
C7
C8
Capacitor, 2.2µF, 6.3V, X5R, Size 0805
Murata(3)
TDK
AVX
2
Murata(3)
Capacitor, 10nF, 50V, X7R, Size 0603
1
Capacitor, 39pF, 50V, Size 0603
1
Capacitor, 390pF, 50V, Size 0603
1
Capacitor, 100pF, 50V, Size 0603
1
AVX
Murata(3)
TDK(2)
(1)
AVX
Murata(3)
06035A391JAT2A
(1)
C1608COG1H101J
Capacitor, 1nF, 50V, COG, Size 0603
(1)
1
Capacitor, 1nF, 50V, X7R, Size 0603
(2)
TDK(2)
06035A101JT2A
June 2011
Capacitor, 2.2µF, 6.3V, X7R, Size 0805
TDK(2)
1608COG1H391J
GRM188R71H101JA01
C9
Murata
06035C103KAT2A
GRM188R71H391JA01
2
Capacitor, 2.2µF, 6.3V, X5R, Size 0805
(3)
(1)
06035A390JAT2A
Capacitor, 22µF, 6.3V, X5R, Size 0805
AVX(1)
TDK(2)
C1608COG1H390J
Qty.
Murata(3)
C1608X7R1H103K
GRM188R71H390JA01
Description
(1)
08056D226MAT
GRM21BR60J226ME39L
C3
Manufacturer
AVX
Murata(3)
TDK(2)
(1)
AVX
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MIC22400
Bill of Materials (Continued)
Item
Part Number
GRM31CR60J476ME19
C10, C11
CIN
L1
Manufacturer
Description
Qty.
(3)
Murata
C3216X5R0J476M
TDK(2)
12066D476MAT2A
(1)
AVX
B41125A3477M
Epcos
Capacitor, 47µF, 6.3V, X5R, Size 1206
2
470µF, 10V, Electrolytic, 8x10-case
(5)
FP3-1R0-R( 7.2x6.7x3mm )
Cooper
Inductor, 1µH, 6.26A
1
CDRH8D28NP-1R0NC ( 8x6x3mm )
Sumida(6)
Inductor, 1µH, 8A
1
Inductor, 1µH, 12A
1
SPM6530T-1R0M120 ( 7x6.5x3mm )
(2)
TDK
(4)
R1
CRCW06031101FKEYE3
Vishay
Resistor, 1.1k, 1%, Size 0603
1
R2
CRCW06036980FKEYE3
Vishay(4)
Resistor, 698, 1%, Size 0603
1
R3
CRCW06032002FKEYE3
Vishay(4)
Resistor, 20k, 1%, Size 0603
1
R4
CRCW06034752FKEYE3
(4)
Vishay
Resistor, 47.5k, 1%, Size 0603
1
R5
CRCW06031003FKEYE3
Vishay(4)
Resistor, 100k, 1%, Size 0603
1
(4)
Resistor, 2.2Ω, 1%, Size 0603
1
(4)
Resistor, 49.9Ω, 1%, Size 0603
1
(4)
R6
CRCW06032R20FKEA
R7
CRCW060349R9FKEA
Vishay
Vishay
Q1
2N7002E
Vishay
Open
1
U1
MIC22400YML
Micrel(7)
Integrated 4A Synchronous Buck Regulator
1
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.
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MIC22400
PCB Layout Recommendations
Top Silk
Top Layer
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MIC22400
PCB Layout Recommendations (Continued)
Mid Layer 1
Mid Layer 2
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MIC22400
PCB Layout Recommendations (Continued)
Bottom Silk
Bottom Layer
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MIC22400
Package Information
20-Pin 3mm x 4mm MLF® (ML)
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MIC22400
Package Information (Continued)
20-Pin ePad TSSOP (TS)
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MIC22400
Recommended Landing Pattern
20-Pin 3mm x 4mm MLF® (ML)
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MIC22400
Recommended Landing Pattern (Continued)
20-Pin ePad TSSOP (TS)
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.
© 2008 Micrel, Incorporated.
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