MIC22705

MIC22705
1MHz, 7A Integrated Switch High-Efficiency
Synchronous Buck Regulator
General Description
Features
The Micrel MIC22705 is a high-efficiency, 7A integrated
switch synchronous buck (step-down) regulator. The
MIC22705 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 MIC22705 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 MIC22705 is available in a 24-pin 4mm 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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•
•
•
•
•
•
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Input voltage range: 2.9V to 5.5V
Output voltage adjustable down to 0.7V
Output load current up to 7A
Safe start-up into a pre-biased output load
Full sequencing and tracking capability
Power Good output
Efficiency >95% across a broad load range
Ultra-fast transient response
Easy RC compensation
100% maximum duty cycle
Fully-integrated MOSFET switches
Thermal-shutdown and current-limit protection
24-pin 4mm x 4mm MLF®
–40°C to +125°C junction temperature range
Applications
•
•
•
•
•
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
95
EFFICIENCY (%)
90
2.5V
85
80
75
70
65
VIN = 5.0V
60
55
50
0
MIC22705 7A 1MHz Synchronous Output Converter
1
2
3
4
5
6
7
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
November 12, 2013
111213-1.1
Micrel, Inc.
MIC22705
Ordering Information
Part Number
Voltage
MIC22705YML
Adjustable
Junction Temperature Range
–40°C to +125°C
Package
24-Pin 4mm x 4mm MLF
Lead Finish
®
Pb-Free
Note:
MLF is a GREEN RoHs-compliant package. Lead finish is NiPdAu. Mold component is Halogen free.
Pin Configuration
24-Pin 4mm × 4mm MLF® (ML)
Pin Description
Pin Number
Pin Name
1, 6, 13, 18
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.
2
EN/DLY
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.
3
NC
4
RC
5
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.
14
FB
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.
November 12, 2013
Description
No Connect: Leave this pin open. Do not connect to ground or route other signals through this
pin.
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.
2
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Micrel, Inc.
MIC22705
Pin Description (Continued)
Pin Number
Pin Name
Description
15
COMP
Compensation Pin (Input): The MIC22705 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.
16
SGND
Signal Ground: Internal signal ground for all low power circuits.
17
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.
7, 12, 19, 24
PGND
Power Ground: Internal ground connection to the source of the internal N-Channel MOSFETs.
8, 9, 10, 11,
20, 21, 22, 23
SW
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.
EP
GND
Exposed Pad (Power): Must be connected to the GND plane for full output power to be realized.
November 12, 2013
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111213-1.1
Micrel, Inc.
MIC22705
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
Supply Voltage ................................................. 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
4mm x 4mm MLF®-24 (θJC)................................ 14°C/W
4mm x 4mm MLF®-24 (θJA) ................................ 40°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)
Undervoltage 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
VFB = 0.9V (not switching)
VEN/DLY = 0V
2.75
420
0.85
5
1.3
10
0.686
0.7
0.2
0.2
10
0.714
V
%
%
nA
1.14
1.34
1.3
V
mV
µA
IOUT = 100mA to 7A
VIN = 2.9V to 5.5V; IOUT = 100mA
VFB = 0.5V
VEN/DLY = 0.5V; VIN = 2.9V and VIN = 5.5V
0.7
1.24
10
1.0
VRC = 0.35V
0.7
1.0
1.3
µA
1.0
1.2
VFB ≤ 0.5V
0.8
100
MHz
%
VFB = 0.5V
7
11
21
A
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.
November 12, 2013
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MIC22705
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
Internal FETs
Condition
Min.
Typ.
Max.
Top MOSFET RDS(ON)
VFB = 0.5V, ISW = 1A
30
Bottom MOSFET RDS(ON)
VFB = 0.9V, ISW = -1A
25
SW Leakage Current
PVIN = 5.5V, VSW = 5.5V, VEN = 0V
60
VIN Leakage Current
PVIN = 5.5V, VSW = 0V, VEN = 0V
25
Units
mΩ
mΩ
µA
Power Good (PG)
PG Threshold
Threshold % of VFB from VREF
Hysteresis
−7.5
−10
−12.5
%
2.0
%
mV
PG Output Low Voltage
IPG = 5mA (sinking), VEN/DLY = 0V
144
PG Leakage Current
VPG = 5.5V; VFB = 0.9V
1.0
Thermal Protection
Over-temperature Shutdown
Over-temperature Shutdown
Hysteresis
TJ Rising
160
°C
20
°C
November 12, 2013
5
2.0
μA
111213-1.1
Micrel, Inc.
MIC22705
Typical Characteristics
20
10
5
VOUT = 1.8V
0.707
FEEDBACK VOLTAGE (V)
15
IOUT = 0A
SWITCHING
16
12
8
4
0
2.5
3.0
3.5
4.0
4.5
5.0
3.0
4.0
4.5
5.0
5.5
2.5
IOUT = 0A to 7A
0.6%
0.4%
10
5
VOUT = 1.8V
0
4.5
5.0
2.5
5.5
3.0
3.5
4.0
4.5
5.0
5.5
1.2
1.1
1.0
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
November 12, 2013
900
800
3.0
5.0
5.5
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
Power Good Threshold/VREF Ratio
vs. Input Voltage
4
100%
3
2
1
95%
90%
85%
VREF = 0.7V
VEN/DLY = 0V
80%
0
2.5
5.5
1000
2.5
VPG THRESHOLD/VREF (%)
ENABLE INPUT CURRENT (µA)
RISING
1.3
5.0
VOUT = 1.8V
Enable Input Current
vs. Input Voltage
Enable Threshold
vs. Input Voltage
1.4
4.5
IOUT = 0A
1100
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1.5
4.0
Switching Frequency
vs. Input Voltage
15
0.0%
3.5
1200
0.2%
4.0
3.0
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (kHz)
VOUT = 1.8V
CURRENT LIMIT (A)
TOTAL REGULATION (%)
3.5
20
3.5
VOUT = 1.8V
Current Limit
vs. Input Voltage
1.0%
3.0
0.697
INPUT VOLTAGE (V)
Load Regulation
vs. Input Voltage
2.5
0.700
0.693
2.5
5.5
INPUT VOLTAGE (V)
0.8%
0.704
VEN/DLY = 0V
0
ENABLE THRESHOLD (V)
Feedback Voltage
vs. Input Voltage
20
SHUTDOWN CURRENT (µA)
SUPPLY CURRENT (mA)
VIN Shutdown Current
vs. Input Voltage
VIN Operating Supply Current
vs. Input Voltage
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)
111213-1.1
Micrel, Inc.
MIC22705
Typical Characteristics (Continued)
VIN Operating Supply Current
vs. Temperature
15.0
10.0
VIN = 5.0V
VOUT = 1.8V
5.0
IOUT = 0A
SWITCHING
15
10
VIN = 5.0V
5
IOUT = 0A
-20
10
40
70
100
130
-50
-20
40
70
100
130
-50
IOUT = 0A
0.700
0.697
0.693
40
70
100
0.8%
VOUT = 1.8V
IOUT = 0A to 7A
0.6%
0.4%
0.2%
130
-20
TEMPERATURE (°C)
Switching Frequency
vs. Temperature
10
40
70
100
1000
900
800
10
40
70
100
TEMPERATURE (°C)
November 12, 2013
0.1%
-20
130
10
40
70
100
130
TEMPERATURE (°C)
Current Limit
vs. Temperature
20
VIN = 5.0V
1.4
RISING
1.3
1.2
1.1
VOUT = 1.8V
15
10
5
VIN = 5V
0
1.0
-20
0.2%
-50
CURRENT LIMIT (A)
ENABLE THRESHOLD (V)
IOUT = 0A
-50
IOUT = 0A
0.3%
130
1.5
1100
VOUT = 1.8V
Enable Threshold
vs. Temperature
VOUT = 1.8V
130
VIN = 2.9V to 5.0V
0.4%
TEMPERATURE (°C)
VIN = 5.0V
100
0.0%
-50
1200
70
0.5%
VIN = 5.0V
0.0%
10
40
Line Regulation
vs. Temperature
LINE REGULATION (%)
LOAD REGULATION (%)
VOUT = 1.8V
10
TEMPERATURE (°C)
1.0%
VIN = 5.0V
-20
-20
Load Regulation
vs. Temperature
0.707
FEEDBACK VOLTAGE (V)
10
TEMPERATURE (°C)
Feedback Voltage
vs. Temperature
-50
2.4
2.2
TEMPERATURE (°C)
0.704
RISING
2.6
FALLING
0
-50
2.8
VEN/DLY = 0V
0.0
SWITCHING FREQUENCY (kHz)
3.0
VIN THRESHOLD (V)
20
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
20.0
VIN UVLO Threshold
vs. Temperature
VIN Shutdown Current
vs. Temperature
-50
-20
10
40
70
TEMPERATURE (°C)
7
100
130
-50
-20
10
40
70
100
130
TEMPERATURE (°C)
111213-1.1
Micrel, Inc.
MIC22705
Typical Characteristics (Continued)
Feedback Voltage
vs. Output Current
Efficiency
vs. Output Current
100
0.5%
95
5.0VIN
90
85
VOUT = 1.8V
LINE REGULATION (%)
FEEDBACK VOLTAGE (V)
0.707
3.3VIN
EFFICIENCY (%)
Line Regulation
vs. Output Current
0.704
0.700
0.697
VIN = 5.0V
VIN = 2.9V to 5.5V
0.4%
VOUT = 1.8V
0.3%
0.2%
0.1%
VOUT = 1.8V
80
0.0%
0.693
0
1
2
3
4
5
6
7
0
1
OUTPUT CURRENT (A)
3
4
5
6
VIN = 3.3V
VIN = 5.0V
VOUT = 1.8V
IOUT = 0A
800
3.2
3.1
3.0
2.9
2.8
0
1
2
3
4
5
6
7
1
OUTPUT CURRENT (A)
2
3
4
5
6
1.8V
1.5V
80
VIN = 3.3V
1.2V
1.0V
0.9V
0.8V
75
70
2
3
4
5
6
7
OUTPUT CURRENT (A)
November 12, 2013
4.8
4.7
0
1
8
3
4
5
6
7
100
VOUT = 0.8V, 1.0V, 1.2V, 1.5V, 1.8V, 2.5V
1.5
1
0.5
0
9
2
Case Temperature* (VIN = 3.3V)
vs. Output Current
CASE TEMPERATURE (°C)
POWER DISSIPATION (W)
2.5V
1
4.9
OUTPUT CURRENT (A)
VIN = 3.3V
0
5.0
7
2
85
7
VIN = 5.0V
IC Power Dissipation vs. Output
Current (VIN = 3.3V)
Efficiency (VIN = 3.3V)
vs. Output Current
90
6
VFB < 0.7V
OUTPUT CURRENT (A)
95
5
4.6
0
100
4
5.1
VFB < 0.7V
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1000
3
5.2
3.3
1100
2
Output Voltage (VIN = 5.0V)
vs. Output Current
3.4
900
1
OUTPUT CURRENT (A)
Output Voltage (VIN = 3.3V)
vs. Output Current
1200
EFFICIENCY (%)
0
7
OUTPUT CURRENT (A)
Switching Frequency
vs. Output Current
SWITCHING FREQUENCY (kHz)
2
80
60
40
VIN = 3.3V
20
VOUT = 1.8V
0
0
2
4
OUTPUT CURRENT (A)
8
6
0
1
2
3
4
5
6
7
OUTPUT CURRENT (A)
111213-1.1
Micrel, Inc.
MIC22705
Typical Characteristics (Continued)
IC Power Dissipation vs. Output
Current (VIN = 5V)
Efficiency (VIN = 5.0V)
vs. Output Current
Case Temperature* (VIN = 5.0V)
vs. Output Current
2
100
100
EFFICIENCY (%)
95
90
3.3V
2.5V
85
1.8V
1.5V
80
1.2V
VIN = 5.0V
75
1.0V
0.9V
0.8V
1.5
1
0.5
0
70
0
1
2
3
4
5
6
7
OUTPUT CURRENT (A)
8
9
CASE TEMPERATURE (°C)
POWER DISSIPATION (W)
VIN = 5V
VOUT = 0.8V, 1.0V, 1.2V, 1.5V, 1.8V, 2.5V, 3.3V
80
60
40
VIN = 5V
20
VOUT = 1.8V
0
0
2
4
OUTPUT CURRENT (A)
6
0
1
2
3
4
6
5
7
OUTPUT CURRENT (A)
Die Temperature* : The temperature measurement was taken at the hottest point on the MIC22705 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.
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Micrel, Inc.
MIC22705
Functional Characteristics
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Micrel, Inc.
MIC22705
Functional Characteristics (Continued)
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Micrel, Inc.
MIC22705
Functional Characteristics (Continued)
November 12, 2013
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Micrel, Inc.
MIC22705
Functional Diagram
Figure 1. MIC22705 Functional Diagram
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Micrel, Inc.
MIC22705
Inductor Selection
Inductor selection will be determined by the following
(not necessarily in the order of importance):
Application Information
The MIC22705 is a 7A synchronous step-down regulator
IC with a fixed 1MHz, voltage-mode PWM control
scheme. The other features include tracking and
sequencing control for controlling multiple output power
systems, and power-on-reset (POR).
The MIC22705 is a voltage mode, pulse-width
modulation (PWM) regulator. 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 MIC22705 will run at 100% duty
cycle.
The MIC22705 provides constant switching at 1MHz with
synchronous internal MOSFETs. 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 NChannel MOSFET provides the current during the off
cycle, very-low amount of power is dissipated during the
off period.
The 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.
Inductance
•
Rated current value
•
Size requirements
•
DC resistance (DCR)
The MIC22705 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
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 MIC22705 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 (in such cases,
the case temperature is not the real dissipation in the
regulator), 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”
sub-section for a more detailed description.
Component Selection
Input Capacitor
A 22µF X5R or X7R dielectrics ceramic capacitor is
recommended on each of the PVIN pins for bypassing. A
Y5V dielectrics 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 MIC22705 was designed specifically for the use of
ceramic output capacitors. The 100µF output capacitor
can be increased to improve transient performance.
Since the MIC22705 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 MIC22705.
November 12, 2013
•
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.
14
111213-1.1
Micrel, Inc.
MIC22705
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
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 an efficiency curve. The portion, from
0A to 0.4A, 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.
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− 
(
V
  OUT × IOUT ) + L PD
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.
Efficiency (VIN = 3.3V)
vs. Output Current
Compensation
The MIC22705 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 100kHz − 200kHz, the MIC22705 is
capable of extremely fast transient responses.
The MIC22705 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.
100
EFFICIENCY (%)
95
90
85
80
VIN = 3.3V
75
IOUT = 1.8V
70
0
1
2
3
4
5
6
7
OUTPUT CURRENT (A)
Figure 2. Efficiency Curve
The region, 1A to 7A, 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.
November 12, 2013

 × 100


15
111213-1.1
Micrel, Inc.
MIC22705
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.
C
22µF ̶ 47µF
47µF ̶ 100µF
100µF ̶ 470µF
0.47µH
0* ̶ 10pF
22pF
33pF
1µH
0 ̶ 15pF
15 ̶ 22pF
33pF
2.2µH
15 ̶ 33pF
33 ̶ 47pF
100 ̶ 220pF
L
†
RC Pin (Soft-Start)
The RC pin provides a trimmed 1µA current source/sink
for accurate ramp up (soft-start). This allows the
MIC22705 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 (as shown in Figure 3).
In the second case, the external capacitor sets the ramp
up and ramp down time of the output voltage. The time
0.7 × C RC
where tRAMP is the time
is given by t RAMP =
1× 10 − 6
from 0 to 100% nominal output voltage.
†
* VOUT > 1.2V, VOUT > 1V
Feedback
The MIC22705 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 =
R1
 VOUT


− 1
V

 REF

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
1.24V. Therefore:
t EN/DLY =
1.24 × C EN/DLY
November 12, 2013
1× 10 − 6
16
111213-1.1
Micrel, Inc.
MIC22705
Pre-Bias Start-Up
The MIC22705 is designed to start-up into a pre-biased
output. This prevents large negative inductor currents
and excessive output voltage oscillations. The
MIC22705 starts with the low-side MOSFET turned off,
preventing reverse inductor current flow. The
synchronous MOSFET stays off until the end of the startup sequence.
If the load current demand is zero or very small at the
time the synchronous MOSFET is enabled, the inductor
current could be discontinuous. In this case, when the
synchronous MOSFET is enabled, the regulator will
transition abruptly from DCM to CCM. This may cause
some small reverse current. If load is applied to keep the
inductor current in CCM, then the transition will be
seamless.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 MIC22705 could be pulled
up or pre-biased 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 MIC22705 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
7A 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
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 theSoft-Start has completed,
the low-side MOSFET will begin switching.
November 12, 2013
17
111213-1.1
Micrel, Inc.
MIC22705
Thermal Considerations
The MIC22705 is packaged in a 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:
TJ = TAMB + PDISS × RθJA
Figure 6. EN Turn-Off − 200mA Load
where:
Current Limit
The MIC22705 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 7 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 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 7A 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 25°C/W. The worst case
RθJC of the MLF® 4mm x 4mm is 14oC/W.
RθJA = RθJC + RθCA
RθJA = 14 + 25 = 39°C/W
To calculate the junction temperature for a 50°C
ambient:
TJ = TAMB + PDISS × RθJA
TJ + 50 + (1.8 × 39)
TJ = 120°C
Figure 7. Current-Limit Detail
November 12, 2013
18
111213-1.1
Micrel, Inc.
MIC22705
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 heatsink, resulting in a
lower case measurement.
Two 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-K-36-36)
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, a 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.
November 12, 2013
Sequencing and Tracking
There are four variations which are easily implemented
using the MIC22705. 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 MIC22705’s to
achieve these requirements.
19
111213-1.1
Micrel, Inc.
MIC22705
Window Sequencing:
Time (4.0ms/div)
Delayed Sequencing:
Time (4.0ms/div)
November 12, 2013
20
111213-1.1
Micrel, Inc.
MIC22705
Normal Tracking:
Time (4.0ms/div)
Ratio Metric Tracking:
Time (4.0ms/div)
November 12, 2013
21
111213-1.1
Micrel, Inc.
MIC22705
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 MIC22705 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.
November 12, 2013
•
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
•
22
Place the RC snubber on either side of the board
and as close to the SW pin as possible.
111213-1.1
Micrel, Inc.
MIC22705
Evaluation Board Schematic
Bill of Materials
Item
C1, C2,
C3, C4
Part Number
TDK
08056D226MAT
AVX(2)
GRM21BR60J226ME39L
GRM188R7160J225M
C1608X5R0J225M
C13
GRM188R71H103KA01D
Open(06035C102KAT2A)
C6
Open(GRM188R71H102KA01D)
Open(C1608C0G1H102J)
06035C471KAT2A
C7
GRM188R71H471KA01D
C1608X7RH471K
C9
C10, C11
GRM1555C1H390JZ01D
5
2.2µF/6.3V, Ceramic Capacitor, X5R, Size 0805
1
10nF, 0603, Ceramic Capacitor
1
AVX(2)
Murata(3)
(1)
TDK
Murata(3)
(2)
AVX
1nF/50V, X7R, 0603, Ceramic Capacitor
Murata(3)
(1)
TDK
1
1nF/50V, COG, 0603, Ceramic Capacitor
(2)
AVX
Murata(3)
470pF/50V, X7R, 0603, Ceramic Capacitor
(1)
TDK
Murata(3)
C3216X5R0J476M
TDK(1)
November 12, 2013
22µF/6.3V, 0805, Ceramic Capacitor
Murata
TDK(1)
GRM31CC80G476ME19L
Qty.
(3)
C1005COG1H390J
GRM31CR60J476ME19
Description
(1)
C2012X5R0J226M
06036D225TAAT2A
C5
Manufacturer
39pF/50V, COG, 0402, Ceramic Capacitor
1
47µF/6.3V, X5R, 1206, Ceramic Capacitor
(3)
47µF/6.3V, X5R, 1206, Ceramic Capacitor
(3)
47µF/4V, X6S, 1206, Ceramic Capacitor
Murata
Murata
23
2
111213-1.1
Micrel, Inc.
MIC22705
Bill of Materials (Continued)
Item
C12
L1
CIN
Part Number
C1608C0G1H101J
GRM1555C1H101JZ01D
SPM6530T-1R0M120
Manufacturer
Description
Qty.
(1)
TDK
100pF/50V, COG, 0402, Ceramic Capacitor
Murata(3)
TDK(1)
HCP0704-1R0-R
Coiltronics
BA1851A3477M
Epcos(6)
1µH, 12A, size 7x6.5x3mm
(5)
1µH, 12A, size 6.8x6.8x4.2mm
(4)
1
1
470µF/10V, Elect., 8×11.5
1
R1
CRCW06031101FKEYE3
Vishay
Resistor, 1.1k, 0603, 1%
1
R2
CRCW04026980FKEYE3
Vishay(4)
Resistor, 698Ω, 0603, 1%
1
CRCW06034752FKEYE3
(4)
Resistor, 47.5k, 0603, 1%
1
(4)
Resistor, 20k, 0402, 1%
1
(4)
R3
R4
CRCW04022002FKEYE3
Vishay
Vishay
R5
Open(CRCW06031003FRT1)
Vishay
Resistor, 100k, 0603, 1%
1
R6
CRCW060349R9FKEA
Vishay(4)
49.9Ω Resistor, 1%, Size 0603
1
CRCW06032R20FKEA
(4)
2.2Ω Resistor, 1%, Size 0603
1
Signal MOSFET − SOT23-6
1
1MHz, 7A Integrated Switch High-Efficiency
Synchronous Buck Regulator
1
R7
Open(2N7002E)
Q1
U1
Open(CMDPM7002A)
MIC22705YML
Vishay
(4)
Vishay
Central
(7)
Semiconductor
Micrel, Inc.(8)
Notes:
1. TDK: www.tdk.com.
2. AVX.: www.avx.com.
3. Murata: www.murata.com.
4. Vishay Tel: www.vishay.com.
5. Coiltronics: www.coiltronics.com.
6. Epcos: www.epcos.com.
7. Central Semiconductor: www.centralsemi.com.
8. Micrel, Inc.: www.micrel.com.
November 12, 2013
24
111213-1.1
Micrel, Inc.
MIC22705
PCB Layout Recommendations
MIC22705 Evaluation Board Top Layer
MIC22705 Evaluation Board Top Silk
November 12, 2013
25
111213-1.1
Micrel, Inc.
MIC22705
PCB Layout Recommendations (Continued)
MIC22705 Evaluation Board Mid-Layer 1 (Ground Plane)
MIC22705 Evaluation Board Mid-Layer 2
November 12, 2013
26
111213-1.1
Micrel, Inc.
MIC22705
PCB Layout Recommendations (Continued)
MIC22705 Evaluation Board Bottom Layer
MIC22705 Evaluation Board Bottom Silk
November 12, 2013
27
111213-1.1
Micrel, Inc.
MIC22705
Package Information
24-Pin 4mm × 4mm MLF® (ML)
November 12, 2013
28
111213-1.1
Micrel, Inc.
MIC22705
Recommended Landing Pattern
Red circle indicates Thermal Via. Size should be .300mm − .350mm in diameter, 1.00mm pitch, and it should
be connected to GND plane for maximum thermal performance.
Green rectangle (with shaded area) indicates Solder Stencil Opening on exposed pad area. Size should be
1.00mm × 1.00mm in size, 1.20mm pitch.
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.
November 12, 2013
29
111213-1.1