MIC22601 DATA SHEET (11/05/2015) DOWNLOAD

MIC22601
4 MHz, 6A Integrated Switch
Synchronous Buck Regulator
General Description
Features
The Micrel MIC22601 is a high efficiency 6A Integrated
switch synchronous buck (step-down) regulator. The
MIC22601 is optimized for highest efficiency (greater than
90%), while still switching at 4MHz over a broad load
range with only 0.22µH inductor and down to 22µF output
capacitor. The ultra-high speed control loop keeps the
output voltage within regulation even under extreme
transient load swings commonly found in FPGAs and low
voltage ASICs. The output voltage can be adjusted down
to 0.7V to address all low voltage power needs. A full
range of sequencing and tracking options is available with
the MIC22601. The enable/delay pin, combined with the
power good PG/POR pin, allows multiple outputs to be
sequenced in any way during turn on and turn off. The RC
(Ramp Control™) 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 ΔV on start up.
The MIC22601 is available in a 24-pin 4mm x 4mm MLF®
package with a junction operating temperature 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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•
•
•
•
•
•
•
•
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Input voltage range: 2.6V to 5.5V
4MHz PWM frequency
Adjustable output voltage option down to 0.7V
Output current to 6A
Small Passive components: 0.22µH and 22µF
Full sequence and tracking ability
Power On Reset/Power Good
Ultra fast transient response
– Easy RC compensation
100% maximum duty cycle
Fully integrated MOSFET switches
Micro power shutdown
Thermal shutdown and current limit protection
24-pin 4mmx4mm MLF® package
–40°C to +125°C junction temperature range
Applications
•
•
•
•
•
•
High power density point of load conversion
Servers and routers
Blu-ray/DVD players and recorders
Computer peripherals
Base stations
FPGA, DSP and low voltage ASIC power
_____________________________________________________________________________________________________________________________________
Typical Application
100
Efficiency
vs. Load Current
90
80
VIN = 3.6V
VIN = 5V
70
60
50
40
0
VOUT = 3.3V
TA = 25°C
L = 470nF
1
2
3
4
5
OUTPUT CURRENT (A)
6
Figure 1. Typical Application Circuit, 6A 4MHz Synchronous Output Converter
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
May 2009
M9999-050509-A
Micrel, Inc.
MIC22601
Ordering Information
Part Number
Voltage
Junction Temp. Range
Package
Lead Finish
MIC22601YML
Adj.
–40° to +125°C
24-Pin 4x4 MLF®
Pb-Free
®
Note: MLF is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
PGND
SW
SW
SW
SW
PGND
Pin Configuration
PVIN
PVIN
EN
SVIN
DELAY
SGND
EP
RC
COMP
PGND
SW
SW
SW
PVIN
SW
FB
PGND
POR
PVIN
24-Pin 4mm x 4mm MLF® (ML)
Pin Description
May 2009
Pin Number
Pin Name
1, 6, 13, 18
PVIN
Power Supply Voltage (Input): Requires bypass capacitor to GND.
Pin Name
17
SVIN
Signal Power Supply Voltage (Input): Requires bypass capacitor-toGND.
2
EN
Enable/Delay (Input): This pin has a 1.24V band gap reference. When
the pin is pulled higher than this 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 VIN. 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.
4
RC
Ramp Control: A capacitor-to-ground from this pin determines the slew
rate of the output voltage during start-up. This can be used for tracking
capability as well as soft start.
14
FB
Feedback: Input to the error amplifier, connect to the external resistor
divider network to set the output voltage.
15
COMP
5
POR/PG
7, 12, 19, 24
PGND
Compensation pin (Input): Place a RC-to-GND to compensate the
device, refer to the applications section.
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. High when the Power is Good
Power Ground (Signal): Ground
16
SGND
Signal Ground (Signal): Ground
3
DELAY
Delay (Input): Add a capacitor to set the delay from FB reaching 90%
nominal to POR asserting high.
8, 9, 10, 11,
20, 21, 22, 23
SW
EP
GND
Switch (Output): Internal power MOSFET output switches.
Exposed Pad (Power): Must make a full connection to a GND plane for
full output power to be realized.
2
M9999-050509-A
Micrel, Inc.
MIC22601
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VIN) .........................................................6V
Output Switch Voltage (VSW) ............................................6V
Output Switch Current (ISW).......................Internally Limited
Logic Input Voltage (VEN, VLQ)........................... VIN to –0.3V
Storage Temperature (Ts) .........................–65°C to +150°C
Lead Temperature (soldering 10sec.)........................ 260°C
EDS Rating(3) ................................................................+2kV
Supply Voltage (VIN)......................................... 2.6V to 5.5V
Junction Temperature (TJ) ..................–40°C ≤ TJ ≤ +125°C
Thermal Resistance
4mm x 4mm MLF-24 (θJC) ................................. 14ºC/W
4mm x 4mm MLF-24 (θJA) .................................40°C/W
Electrical Characteristics(4)
TA = 25°C with VIN = VEN = 3.3V; VOUT = 1.8V, unless otherwise specified. Bold values indicate –40°C≤ TJ ≤ +125°C.
Parameter
Supply Voltage Range
Under-Voltage Lockout Threshold
UVLO Hysteresis
Quiescent Current, PWM Mode
Shutdown Current
[Adjustable] Feedback Voltage
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
Oscillator Frequency 22601
EN/DLY Threshold Voltage
EN/DLY Source Current
Condition
Min
(turn-on)
2.6
2.4
VEN =>1.34V; VFB = 0.9V (not switching)
VEN = 0V
± 2% (over temperature)
VFB = 0.9*VNOM
VOUT 1.8V; VIN = 2.6 to 5.5V, ILOAD= 100mA
100mA < ILOAD < 6000mA, Vin = 3.3V
VFB ≤ 0.5V
ISW = 1000mA; VFB=0.5V
ISW = -1000mA; VFB=0.9V
6
VIN = 2.6 to VIN = 5.5V
Ramp Control Current
0.7
Power On Reset IPG(LEAK)
VPORH = 5.5V; POR = High
Power On Reset VPG(LO)
Output Logic-Low Voltage (undervoltage condition),
IPOR = 5mA
Threshold, % of VOUT below nominal
Over-Temperature Shutdown
Over-Temperature Shutdown
Hysteresis
Units
5.5
2.6
0.03
0.025
4
1.24
1
4.8
1.34
1.3
1
1.3
µA
1
2
µA
µA
1
10
0.2
0.2
1300
10
0.714
14
100
RC Pin IRAMP
Hysteresis
Max
V
V
mV
µA
µA
V
nA
A
%
%
%
Ω
Ω
MHz
V
µA
2.5
280
850
5
0.686
3.2
1.14
0.7
Power On Reset VPG
Typ
130
7.5
10
mV
12.5
%
2
%
160
20
°C
°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.
May 2009
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M9999-050509-A
Micrel, Inc.
MIC22601
Typical Characteristics
RDSON (mO)
3.8
3.6
120
80
100
60
40
REFERENCE VOLTAGE (V)
120
25
20
15
5
120
100
40
20
0
4.2
4
3.8
3.6
2.0
30
0
2.5
Switching Frequency
vs. Input Voltage
4.4
3.2
2.5
vs. Input Voltage
10
VIN = 3.3V
VIN = 3.3V
3.4
OUTPUT VOLTAGE (V)
45
4.0
-20
0.690
P-Channel RDSON
4.2
-40
0.692
VIN = 5.5V
TEMPERATURE (°C)
35
May 2009
0.696
0.694
FREQUENCY (MHz)
1.14
1.12
4.4
TEMPERATURE (°C)
0.698
4.6
1.18
1.16
40
3.4
0.702
0.700
4.8
1.20
Switching Frequency
vs. Temperature
Reference Voltage
vs. Temperature
TEMPERATURE (°C)
1.24
1.22
1.10
5.5
0.704
Enable Voltage
vs. Temperature
80
5.5
6
1.28
1.26
4.6
3.2
3.5 4 4.5 5 5.5
INPUT VOLTAGE (V)
100
3.5
4
4.5
5
INPUT VOLTAGE (V)
80
FREQUENCY (MHz)
4.8
TA = 25°C
3
3
TA = 25°C
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
0.708
0.706
-40
0.690
2.5
60
1.1
2.5
TA = 25°C
0.692
40
1.14
120
0.694
0
1.16
80
0.696
-40
1.2
1.18
60
0.698
ENABLE VOLTAGE (V)
1.22
60
ENABLE VOLTAGE (V)
1.24
40
0.700
1.30
1.26
20
0.702
1.28
1.12
0
0.704
Enable Level
vs. Input Voltage
1.3
0.710
0.706
-20
TEMPERATURE (°C)
120
80
40
20
0
-20
-40
0
100
VIN = 3.3V
0.1
0.2
0
2.5
Reference Voltage
vs. Input Voltage
20
REFERENCE VOLTAGE (V)
0.708
60
INPUT CURRENT (mA)
0.710
0.3
0.2
0.4
TEMPERATURE (°C)
0.9 Not Switching FB = 1V
0.8
0.4
-20
-40
0
VIN = 3.3V
0.6
20
3
2
0.8
0
4
1.0
-20
6
5
1.0
0.6
0.5
INPUT CURRENT (mA)
7
Quiescent Current
vs. Temperature
0.7
Not Switching FB = 1V
1
1
TA = 25°C
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
INPUT VOLTAGE (V)
1.2
9
8
100
5
4
3
2
Quiescent Current
vs. Input Voltage
Shutdown Current
vs. Temperature
10
9
8
7
6
INPUT CURRENT (µA)
INPUT CURRENT (µA)
10
Shutdown Current
vs. Input Voltage
TCASE = 90°C
3
3.5
4
4.5
5
INPUT VOLTAGE (V)
4
5.5
TCASE = 25°C
3
3.5
4
4.5
5
INPUT VOLTAGE (V)
5.5
Output Voltage
vs VRC
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
V
0.2
0.4
0.6
VRC (V)
OUT
= 1.8V
0.8
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M9999-050509-A
Micrel, Inc.
MIC22601
Typical Characteristics (continued)
100
Efficiency
vs. Output Current
VIN = 2.5V
90
80
60
60
VOUT = 3.3V
TA = 25°C
L = 470nF
Bode (5V to 1.8V - 6A)
470nH and 47µF
40
30
Phase
20
10
Gain
0
40
0
6
180
50
144
40
30
108
72
36
0
20
10
0
100µF OSCON on VIN
1
May 2009
10
100
1000 10000
FREQUENCY (kHz)
70
VIN = 3.3V
VIN = 5V
60
VOUT = 1.8V
TA = 25°C
L = 470nF
1
2
3
4
5
OUTPUT CURRENT (A)
Bode (3.3V to 1.8V - 6A)
470nH and 47µF
Phase
50
180
50
144
40
30
108
72
36
0
Gain
40
0
6
20
10
0
100µF OSCON on VIN
1
Efficiency
vs. Output Current
80
VIN = 5V
50
GAIN (dB)
50
1
2
3
4
5
OUTPUT CURRENT (A)
90
80
70
50
GAIN (dB)
VIN = 5V
70
40
0
VIN = 3.6V
90
VIN = 3.6V
100
GAIN (dB)
100
Efficiency
vs. Load Current
10
100
1000 10000
FREQUENCY (kHz)
5
VOUT = 1V
L = 470nF
1
2
3
4
5
OUTPUT CURRENT (A)
Bode (5V to 3.3V - 6A)
470nH and 47µF
6
180
144
Phase
108
72
36
Gain
0
100µF OSCON on VIN
1
10
100
1000 10000
FREQUENCY (kHz)
M9999-050509-A
Micrel, Inc.
MIC22601
Functional Characteristics
May 2009
6
M9999-050509-A
Micrel, Inc.
MIC22601
Typical Circuits and Waveforms
Sequencing Circuit and Waveform
Tracking Circuit and Waveform
May 2009
7
M9999-050509-A
Micrel, Inc.
MIC22601
Functional Diagram
Figure 2. IC Block Diagram
May 2009
8
M9999-050509-A
Micrel, Inc.
MIC22601
FB
The feedback pin provides a 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 the “Applications Information”
for more detail.
Functional Description
PVIN
PVIN is the input supply to the internal 30mΩ 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 10µF ceramic is recommended for bypassing
each PVIN supply.
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 Good (PG)
function, the delay can be set to a minimum. This can be
done by removing the Delay capacitor.
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.
RC
RC allows the slew rate of the output voltage to be
programmed by the addition of a capacitor from RC-toground. 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 source 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. In order to achieve the highest efficiency and
reduce internal losses, connect a Schottky diode directly
from this pin-to-ground as close to the package as
possible.
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.
SGND
Internal signal ground for all low power sections.
PGND
Internal ground connection to the source of the internal
N-Channel MOSFETs.
Comp
The MIC22601 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 when using low value, low ESR ceramic
capacitors.
May 2009
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M9999-050509-A
Micrel, Inc.
MIC22601
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, which 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”
below for a more detailed description.
Application Information
The MIC22601 is a 6A Synchronous step down regulator
IC with a fixed 4MHz, voltage mode PWM control
scheme. The other features include tracking and
sequencing control for controlling multiple output power
systems. Power-on-reset and easy RC compensation
are other features as well.
Component selection
Input Capacitor
A minimum 10µF ceramic is recommended on each of
the PVIN pins for bypassing. X5R or X7R dielectrics are
recommended for the input capacitor. Y5V dielectrics,
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.
Enable/DLY Capacitor
Enable/DLY sources 1uA out of the IC to allow a startup
delay to be implemented. The delay time is simply the
time it takes 1uA to charge CDLY to 1.24V. Therefore:
Output Capacitor
The MIC22601 was designed specifically for the use of
ceramic output capacitors. 47µF can be increased to
improve transient performance. Since the MIC22601 is
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
MIC22601.
TDLY =
Inductance
•
Rated current value
•
Size requirements
⎛V
×I
Efficiency % = ⎜⎜ OUT OUT
⎝ VIN × IIN
⎞
⎟⎟ × 100
⎠
Maintaining high efficiency serves two purposes. It
reduces power dissipation in the power supply, reducing
the need for heat sinks and thermal design
considerations and it reduces 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 V.I (during flywheel diode
conduction time) or I2R (during MOSFET conduction
time). 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 off at a
constant 4Mhz frequency and the switching transitions
make up the switching losses.
Although one is not required, a Schottky diode rated for
2A continuous current, connected between SW and
GND can add up to 5% to efficiency. This is achieved by
preventing forward biasing of the internal MOSFET body
•
DC resistance (DCR)
The MIC22601 is designed for use with a 0.22µH 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 1A to the output current level. The
RMS rating should be chosen to be equal or greater than
the Current Limit of the MIC22601 to prevent
overheating in a fault condition. For best electrical
May 2009
1 ⋅ 10 -6
Efficiency considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power consumed.
Inductor Selection
Inductor selection will be determined by the following
(not necessarily in the order of importance):
•
1.24 ⋅ C DLY
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M9999-050509-A
Micrel, Inc.
MIC22601
diodes between switching transitions. The MOSFET
body diode is less efficient for these short current pulses.
Figure 3 shows an efficiency curve. The non-shaded
portion, from 0A to 1A, 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.
Compensation
The MIC22601 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 4Mhz ramp
signal and using the output of the error amplifier to
modulate the pulse width of the switch node, maintaining
output voltage regulation. With a typical gain bandwidth
of 100-200 kHz, the MIC22601 is capable of extremely
fast transient responses.
The MIC22601 is designed to be stable with a typical
application using a 0.22µH inductor and a 47µF ceramic
(X5R) output capacitor. These values can be varied
dependant on the tradeoff between size, cost and
efficiency, keeping the LC natural frequency
1
(
) ideally less than 34kHz to ensure stability
2⋅Π ⋅ L⋅C
can be achieved. The minimum recommended inductor
value is 0.22µH 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
below.
Efficiency 3.6V to 1.8V
L = 470nH (3mm x 3mm)
100
90
80
70
60
50
40
0
1
2
3
4
5
OUTPUT CURRENT (A)
6
Figure 3. Efficiency Curve
The dashed region, 1A to 6A, efficiency loss is
dominated by MOSFET RDS(ON) and inductor DC losses.
Higher input supply voltages will increase the Gate-toSource threshold 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;
LPD = IOUT2 × DCR
From that, the loss in efficiency due to inductor
resistance can be calculated as follows:
⎡
CÆ
22-47µF
47µF100µF
100µF470µF
4.7pF
0*-10pF
0†-15pF
15-33pF
10pF
22pF
15-22pF
33-47pF
15pF
33pF
33pF
100-220pF
LÈ
0.22µH
0.47µH
1µH
2.2µH
⎞⎤
VOUT ⋅ IOUT
⎟⎥ × 100
⎟
⎝ (VOUT ⋅ IOUT ) + LPD ⎠⎦⎥
⎛
Efficiency Loss = ⎢1 − ⎜⎜
* VOUT > 1.2V, VOUT > 1V
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 maybe desired. Larger inductances
reduce the peak-to-peak inductor ripple current, which
minimize losses.
Feedback
The MIC22601 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. To calculate the resistor divider
network for the desired output is as follows:
⎣⎢
May 2009
†
R2 =
11
R1
⎛ VOUT
⎞
⎜⎜
− 1⎟⎟
⎝ VREF
⎠
M9999-050509-A
Micrel, Inc.
MIC22601
After Enable 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 enable 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 VDD1.24V 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
Where VREF is 0.7V, R1 is the upper resistor, R2 is the
lower resistor 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 decoupling capacitor (50pF – 100pF)
across the lower resistor (R2) can reduce noise pick-up
by providing a low impedance path to the ground.
PWM Operation
The MIC22601 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 MIC22601 will run at 100% duty
cycle.
The MIC22601 provides constant switching at 4MHz with
synchronous internal MOSFETs. The internal 30mΩ
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 lowside 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.
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 MIC22601 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 rate of the output voltage. The rate is
0.7 ⋅ C RC
where TRAMP is the time
given by TRAMP =
1 ⋅ 10 -6
from 0% to 100% nominal output voltage.
Sequencing and tracking
The MIC22601 provides additional pins to provide
up/down sequencing and tracking capability for
connecting multiple voltage regulators together.
Tracking & Sequencing examples
There 4 distinct variations which are easily implemented
using the MIC22601. The 2 Sequencing variations are
Delayed and windowed. The 2 tracking variants are ratio
metric and Normal. The following diagrams illustrate
methods for connecting two MIC22601’s to achieve
these requirements.
Enable/DLY pin
The Enable 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.
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 1st up,
last down power sequence.
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MIC22601
Normal Tracking
Sequencing
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Micrel, Inc.
MIC22601
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.
Ratio Metric Tracking
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MIC22601
Where
Current limit
The MIC22601 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.
The circuit in Figure 4 describes the operation of the
current limit circuit. Since the actual RDSON of the PChannel MOSFET varies part-to-part, over temperature
and with input voltage, simple I.R 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 on the RDSON value. Current limit
is set to 9A 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.
•
PDISS is the power dissipated within the MLF®
package and is typically 1.8W at 6A load. This
has been calculated for a 0.47µH inductor and
details can be found in table 1 below for
reference.
VINÆ
VOUT
@5AÈ
1
1.2
1.8
2.5
3.3
3
3.5
4
4.5
5
1.67
1.68
1.70
1.72
1.71
1.72
1.74
1.76
1.78
1.76
1.77
1.79
1.80
1.82
1.81
1.81
1.74
1.85
1.86
1.85
1.86
1.84
1.89
1.91
Table 1. Power dissipation (W) for 5A output
•
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.
• TA is the Operating Ambient temperature.
Example
The Evaluation board has 2 copper planes contributing
to an RθCA of approximately 25°C/W. The worst case
RθJC of the MLF® 4x4 is 14°C/W.
RθJA = RθJC + RθCA
RθJA = 14 + 25 = 39°C/W
Figure 4. Current Limit Detail
Thermal considerations
The MIC22601 is packaged in the MLF® 4mm 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:
To calculate the junction temperature for a 50°C
ambient:
TJ = TAMB+PDISS. RθJA
TJ = 50 + (1.8 x 39)
TJ = 120°C
This is below our maximum of 125°C.
TJ = TA + PD · RθJA
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MIC22601
Schematic
U1
MIC22601YML
SVIN
J1
+VIN
C1
22µF
C3
22µF/6.3V
J2
GND
C2
22µF
C4
22µF
SVIN
C5
J3
EN
1
6
13
18
PVIN
PVIN
PVIN
PVIN
17
SVIN
22µF/6.3V
C6
1nF
SVIN
7
12
19
SGND
EP
POR
5
PGND
Delay
C8
1nF
PGND
RC
3
PGND
EN
4
PGND
C7
10nF
2
24
16
SW
SW
SW
SW
SW
SW
SW
SW
8
9
10
11
20
21
22
23
FB
14
Comp
15
L1
0.22µH
D1
C10
C11
47µF/6.3V
J7
+VOUT
1.8V@6A
47µF/6.3V
R1
C9
15pF
R4
20k
R2
698
1.1k
C12
100pF
J8
GND
R3
47.5k
J11
POR
Bill of Materials
Item
C1, C2, C3,
C4, C5
Part Number
C2012X5R0J226M
08056D226MAT
GRM21BR60J226ME39L
C6
Open
Manufacturer
TDK
Description
Qty
22µF/6.3V, 0805 Ceramic Capacitor
5
Open, 0603 Ceramic Capacitor
NA
(1)
AVX(2)
(3)
Murata
NA
(3)
C7
GRM188R71H103KA01D
Murata
10nF, 0603 Ceramic Capacitor
1
C8
VJ0603Y102KXQCW1BC
Vishay(4)
1nF, 0603 Ceramic Capacitor
1
C9
C1005COG1H150J
TDK(1)
15pF, 0402 Ceramic Capacitor
1
C3216X5R0J476M
(1)
TDK
GRM31CR60J476ME19
Murata
47µF/6.3V, 1206 Ceramic Capacitor
2
100pF, 0603 Ceramic Capacitor
1
2A, 20V Schottky Diode
1
0.22µH, 9.5A
1
1.1k, 0603 Resistor
1
C10, C11
C12
R1
(3)
GRM31CC80G476ME19L
Murata
VJ0402A101KXQCW1BC
Vishay(4)
D1
L1
(3)
(4)
SS2P2L
Visyay
DFLS220
Diodes, Inc.
IHLP1616ABERR22M01
CRCW06031101FKEYE3
(5)
Vishay(4)
(4)
Vishay
(4)
R2
CRCW04026980FKEYE3
Vishay
698Ω, 0603 Resistor
1
R3
CRCW06034752FKEYE3
Vishay(4)
47.5k, 0603 Resistor
1
R4
CRCW04022002FKEYE3
Vishay(4)
20k, 0402 Resistor
1
Integrated 6A Synchronous Buck Regulator
1
U1
MIC22601YML
Micrel
(6)
Notes:
1. TDK: www.tdk.com
2. AVX: www.avx.com
3. Murata: www.murata.com
4. Vishay: www.vishay.com
5. Diodes, Inc.: www.diodes.com
6. Micrel: www.micrel.com
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MIC22601
PCB Layout Recommendation
Top Assembly
Top Layer
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Micrel, Inc.
MIC22601
Package Information
24-Pin 4mm x 4mm MLF® (ML)
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
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
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.
© 2009 Micrel, Incorporated.
May 2009
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