MIC4782YMLTR [MICROCHIP]
SWITCHING CONTROLLER, PQCC16, 3 X 3 MM, GREEN, MLF-16;
| 型号： | MIC4782YMLTR |
| 厂家： | 
MICROCHIP |
| 描述： | SWITCHING CONTROLLER, PQCC16, 3 X 3 MM, GREEN, MLF-16 开关 |
| 文件： | 总23页 (文件大小：660K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC4782
1.8 MHz Dual 2A Integrated Switch
Buck Regulator
General Description
Features
The Micrel MIC4782 is a high efficiency dual PWM buck
(step-down) regulator that provides dual 2A output current.
The MIC4782 operates at 1.8MHz. A proprietary internal
compensation technique allows a closed loop bandwidth of
over 200kHz.
•
•
•
•
•
•
•
•
•
3.0 to 6.0V supply voltage
1.8MHz PWM mode
2A dual output
Greater than 92% efficiency
100% maximum duty cycle
Adjustable output voltage option down to 0.6V
Ultra-fast transient response
Ultra-small external components
The low on-resistance internal P-Channel MOSFET of the
MIC4782 allows efficiencies over 92%, reduces external
components count and eliminates the need for an
expensive current sense resistor.
Stable with a 1µH inductor and a 4.7µF output
capacitor
The MIC4782 operates from 3.0V to 6.0V input and the
output can be adjusted down to 0.6V. The device can
operate with a maximum duty cycle of 100% for use in low-
dropout conditions.
•
•
•
•
•
Fully integrated 2A MOSFET switches
Micro-power shutdown
The MIC4782 is available in the exposed pad 16-pin
3mm x 3mm MLF® with a junction operating range from
–20°C to +125°C.
Thermal shutdown and current limit protection
Available in a 3mm × 3mm 16-pin MLF®
–20°C to +125°C junction temperature range
All support documentation can be found on Micrel’s web
site at: www.micrel.com.
Applications
•
•
•
•
•
•
Broadband: xDSL modems
Automotive satellite radios
HD STB, DVD/TV recorder
Computer peripherals: printers and graphic cards
FPGA/ASIC
General point-of-load
Typical Application
5.0VIN, 3.3VOUT Efficiency
100
98
96
94
92
90
88
86
84
82
80
0
0.4
0.8
1.2
1.6
2
OUTPUT CURRENT (A)
2A, 1.8MHz Dual Buck Regulator
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
M9999-081709-D
August 2009
1
Micrel, Inc.
MIC4782
Ordering Information
Part Number
MIC4782YML
Note:
Voltage
Junction Temp. Range
Package
16-Pin 3mm x 3mm MLF®
Lead Finish
Adj.
–20° to +125°C
Pb-Free
MLF® is a GREEN RoHS-compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configuration
16-Pin 3mm x 3mm MLF® (YML)
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MIC4782
Pin Description
Pin Number
Pin Name
Pin Function
1
FB2
Feedback for output 2 (Input). Input to the error amplifier, connect to the external resistor
divider network to set the output voltage.
2(1)
EN2
Enable for output 2 (Input). Logic level low, will shutdown the device, reducing the current
draw to 1.6µA typical. (both EN1 and EN2 are low).
3,4
5
SW2
Switch for output 2 (Output): Internal power P-Channel MOSFET output switch
Power Ground for output 2. Provides the ground return path for the high-side drive current.
PGND1 pin and PGND2 pin are internally connected by anti-parallel diodes.
PGND2
6,15
7,14
8
VIN2
VIN1
Supply Voltage for output 2 (Input): Supply voltage for the source of the internal P-channel
MOSFET and driver. Requires bypass capacitor-to-GND.
VIN1 pins and VIN2 pins are internally connected by anti-parallel diodes.
Supply Voltage for output 1 (Input): Supply voltage for the source of the internal P-channel
MOSFET and driver. Requires bypass capacitor-to-GND.
VIN1 pins and VIN2 pins are internally connected by anti-parallel diodes.
PGND1
Power Ground for output 1. Provides the ground return path for the high-side drive
current.
PGND1 pin and PGND2 pin are internally connected by anti-parallel diodes.
Switch for output 1 (Output): Internal power P-Channel MOSFET output switch
9,10
11(1)
SW1
EN1
Enable for output 1 (Input). Logic level low, will shutdown the device, reducing the current
draw to 1.6µA typical. (both EN1 and EN2 are low).
12
FB1
Feedback for output 1 (Input). Input to the error amplifier, connect to the external resistor
divider network to set the output voltage.
13
16
SGND
BIAS
Signal (Analog) Ground. Provides return path for control circuitry and internal reference.
Internal circuit bias supply. Must be bypassed with a 0.1µF ceramic capacitor-to-SGND.
Biased through a 10Ω resistor to VIN.
EPAD
GND
Connect to ground.
Note:
1. Do not float Enable Input.
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MIC4782
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VIN)..................................... –0.3V to +6.5V
Output Switch Voltage (VSW1, VSW2).............. –0.3V to +6.5V
Output Switch Current (ISW1, ISW2)………...Internally Limited
Input Voltage (VEN), (VFB), (VBIAS).......................-0.3V to VIN
Storage Temperature (Ts) .........................–60°C to +150°C
Junction Temperature ................................................ 150°C
Lead Temperature (soldering, 10sec.)....................... 260°C
ESD Rating(3)................................................................. 2KV
Supply Voltage (VIN)........................................... +3V to +6V
Logic Input Voltage (VEN) ....................................... 0V to VIN
Junction Temperature (TJ) ........................–20°C to +125°C
Junction Thermal Resistance
3mm x 3mm MLF® (θJA).....................................60°C/W
Electrical Characteristics(4)
VIN = VEN = 3.6V; L = 1.0µH; COUT = 4.7µF; TA = 25°C, unless noted. Bold values indicate –20°C< TJ < +125°C.
Parameter
Condition
Min
3.0
Typ
Max
6.0
Units
V
Supply Voltage Range
Under-Voltage Lockout Threshold
UVLO Hysteresis
Turn-on
2.45
2.6
100
1.4
1.0
1.6
607
1
2.7
V
mV
mA
mA
µA
mV
nA
A
Quiescent Current
VFB = 0.9 * VNOM (not switching); VIN = 6V
VFB = 0.9 * VNOM (not switching); VIN = 3.6V
VEN = 0V
3.0
Shutdown Current
589
625
[Adjustable] Feedback Voltage
FB pin input current
± 3%, ILOAD = 100µA
Current Limit
VFB = 0.9 * VNOM
2.5
4.3
0.07
0.2
Output Voltage Line Regulation
Output Voltage Load Regulation
Maximum Duty Cycle
VIN = 3V to 6V; ILOAD= 100 µA
20mA < ILOAD < 2A
%
%
100
%
VFB ≤ 0.9 * VNOM
ISW = 50mA VFB =GND
Switch ON-Resistance
155
mΩ
Oscillator Frequency
Switching Phase
1.8
180
0.9
55
MHz
Deg
V
Enable Threshold
0.5
1.3
Enable Hysteresis
mV
µA
°C
Enable Input Current
Over-Temperature Shutdown
Over-Temperature Hysteresis
Notes:
0.1
153
18
°C
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. Human body model, 1.5k in series with 100pF.
4. Specification for packaged product only.
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MIC4782
Typical Characteristics
3.3VIN, 1.0VOUT Efficiency
5.0VIN, 1.0VOUT Efficiency
3.3VIN, 1.2VOUT Efficiency
80
78
76
74
72
70
68
66
64
62
60
84
82
80
78
76
74
72
70
68
66
64
80
78
76
74
72
70
68
66
4.5Vin
5.0Vin
5.5Vin
3.0Vin
3.3Vin
3.6Vin
3.0Vin
3.3Vin
3.6Vin
64
62
60
0
0
0
0.4
0.8
1.2
1.6
2
0
0.4
0.8
1.2
1.6
2
0
0.4
0.8
1.2
1.6
2
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
5.0VIN, 1.2VOUT Efficiency
3.3VIN, 1.5VOUT Efficiency
5.0VIN, 1.5VOUT Efficiency
84
82
80
78
76
74
72
70
68
66
64
88
86
84
82
80
78
76
74
72
70
68
88
86
84
82
80
78
76
74
72
70
68
3.0Vin
3.3Vin
3.6Vin
4.5Vin
5.0Vin
5.5Vin
4.5Vin
5.0Vin
5.5Vin
0
0.4
0.8
1.2
1.6
2
0.4
0.8
1.2
1.6
2
0
0.4
0.8
1.2
1.6
2
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
3.3VIN, 1.8VOUT Efficiency
5.0VIN, 1.8VOUT Efficiency
3.3VIN, 2.5VOUT Efficiency
92
90
88
86
84
82
80
78
76
74
72
92
90
88
86
84
82
80
78
76
74
72
96
94
92
90
88
86
84
82
80
78
76
4.5Vin
5.0Vin
5.5Vin
3.0Vin
3.3Vin
3.6Vin
3.0Vin
3.3Vin
3.6Vin
0
0.4
0.8
1.2
1.6
2
0.4
0.8
1.2
1.6
2
0
0.4
0.8
1.2
1.6
2
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Load Regulation
5.0VIN, 2.5VOUT Efficiency
5.0VIN, 3.3VOUT Efficiency
96
94
92
90
88
86
84
82
80
78
76
100
98
96
94
92
90
88
86
84
82
80
0.615
0.610
0.605
0.600
0.595
4.5Vin
5.0Vin
5.5Vin
4.5Vin
5.0Vin
5.5Vin
Vin=3.3V
1.6 2
0
0.4
0.8
1.2
0
0.4
0.8
1.2
1.6
2
0
0.4
0.8
1.2
1.6
2
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
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August 2009
Micrel, Inc.
MIC4782
Typical Characteristics (continue)
Feedback Voltage
vs. Temperature
Frequency
vs. Temperature
Feedback Voltage
0.6080
0.610
0.609
0.608
0.607
0.606
0.605
0.604
0.603
0.602
0.601
0.600
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
0.6078
0.6076
0.6074
0.6072
0.6070
0.6068
0.6066
0.6064
0.6062
0.6060
-20
0
20
40
60
80
100
120
3
3.6
4.2
4.8
5.4
6
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
Feedback Voltage
vs. Supply Voltage
Quiescent Current
vs. Supply Voltage
Rdson
vs. Supply Voltage
0.8
0.6
0.4
0.2
0.0
1.6
1.2
0.8
0.4
0.0
190
180
170
160
150
140
130
120
110
3
3.6
4.2
4.8
5.4
6
0
1
2
3
4
5
6
0
1
2
3
4
5
6
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
Rdson
vs. Temperature
Enable Threshold
vs. Supply Voltage
Enable Threshold
vs. Temperature
1.2
1.0
0.8
0.6
0.4
0.2
0.0
200
190
180
170
160
150
140
130
120
1.20
1.00
0.80
0.60
0.40
0.20
0.00
3
3.6
4.2
4.8
5.4
6
-20
0
20
40
60
80
100
120
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
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Micrel, Inc.
MIC4782
Functional Characteristics
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MIC4782
Functional Diagram
MIC4782 Block Diagram
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Micrel, Inc.
MIC4782
Pin Description
VIN1/VIN2
SW1/SW2
VIN pins (two pins for VIN1 and two pins for VIN2)
provide power to the source of the internal P-Channel
MOSFET along with the current limiting sensing. VIN1
pins and VIN2 pins are internally connected by anti-
parallel diodes. The VIN operating voltage range is from
3.0V to 6.0V. Due to the high switching speeds, a 10µF
capacitor is recommended close to VIN and the power
ground (PGND) for each pin for bypassing. Please refer
to layout recommendations for more details.
The switch pins (SW1 and SW2) connect directly to the
inductor and provide the switching current necessary to
operate in PWM mode. Due to the high speed switching
on these pins, the switch nodes should be routed away
from sensitive nodes. These pins also connect to the
cathodes of the free-wheeling diodes.
PGND1/PGND2
Power ground pins (PGND1 and PGND2) are the ground
paths for the MOSFET drive current. PGND1 pin and
PGND2 pin are internally connected by anti-parallel
diodes. The current loop for the power ground should be
as small as possible and separate from the Signal
BIAS
The bias (BIAS) provides power to the internal reference
and control sections of the MIC4782. A 10ꢀ resistor
from VIN to BIAS and a 0.1µF from BIAS to SGND are
required for clean operation.
ground (SGND)
loop.
Refer
to
the
layout
recommendation for more details.
EN1/EN2
SGND
The enable pins (EN1 and EN2) provides a logic level
control of the outputs 1 and 2. In the off state, supply
current of the device is greatly reduced (typically <2µA).
Do not drive the enable pin above the supply voltage.
Signal ground (SGND) is the ground path for the biasing
and control circuitry. The current loop for the signal
ground should be separate from the power ground
(PGND) loop. Refer to the layout recommendation for
more details.
FB1/FB2
EPAD
The feedback pins (FB1 and FB2) provides the control
path to control the outputs 1 and 2. A resistor divider
connecting the feedback to the output is used to adjust
the desired output voltage. The output voltage is
calculated as follows:
The exposed pad on the bottom of the part must be
connected to ground.
R1
R2
⎛
⎜
⎞
VOUT = VREF
×
+ 1
⎟
⎝
⎠
where VREF is equal to 0.6V.
A feed-forward capacitor is recommended for most
designs. To reduce current draw, 10Kꢀ feedback
resistors are recommended from the outputs to the FB
pins (R1 in the equation). The large resistor value and
the parasitic capacitance of the FB pin can cause a high
frequency pole that can reduce the overall system phase
margin. By placing a feed-forward capacitor (across R1),
these effects can be significantly reduced. Feed-forward
capacitance (CFF) can be calculated as follows:
1
CFF
=
2π × R1× 200kHz
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Micrel, Inc.
MIC4782
modulating (PWM) the switch voltage to the average
required output voltage. The switching can be broken up
into two cycles; On and Off.
Application Information
The MIC4782 is a dual 2A PWM non-synchronous buck
regulator. By switching an input voltage supply, and
filtering the switched voltage through an inductor and
capacitor, a regulated DC voltage is obtained. Figure 1
shows a simplified example of a non-synchronous buck
converter.
During the On-Time, Figure 3 illustrates the high-side
switch is turned on, current flows from the input supply
through the inductor and to the output. The inductor
current is charged at the rate;
V
− V
)
IN
OUT
L
Figure 1. Example of Non-synchronous Buck Converter
For a non-synchronous buck converter, there are two
modes of operation; continuous and discontinuous.
Continuous or discontinuous refer to the inductor
current. If current is continuously flowing through the
inductor throughout the switching cycle, it is in
continuous operation. If the inductor current drops to
zero during the off time, it is in discontinuous operation.
Critically continuous is the point where any decrease in
output current will cause it to enter discontinuous
operation. The critically continuous load current can be
calculated as follows;
Figure 3. On-Time
To determine the total on-time, or time at which the
inductor charges, the duty cycle needs to be calculated.
The duty cycle can be calculated as;
2
⎡
⎢
⎤
⎥
VOUT
V
−
OUT
V
⎢
⎣
⎥
⎦
IN
IOUT
=
fsw × 2×L
V
OUT
D =
Continuous or discontinuous operation determines how
we calculate peak inductor current.
V
IN
and the On time is;
Continuous Operation
D
TON
=
Figure 2 illustrates the switch voltage and inductor
current during continuous operation.
fsw
Therefore, peak-to-peak ripple current is;
VOUT
(
VIN−VOUT ×
)
V
IN
Ipk−pk
=
fsw ×L
Since the average peak-to-peak current is equal to the
load current. The actual peak (or highest current the
inductor will see in a steady-state condition) is equal to
the output current plus ½ the peak-to-peak current.
VOUT
Figure 2. Continuous Operation
(
V
− VOUT ×
)
IN
V
IN
Ipk = IOUT
+
The output voltage is regulated by pulse width
2× fsw ×L
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MIC4782
Figure 4 demonstrates the off-time. During the off-time,
the high-side internal P-channel MOSFET turns off.
Since the current in the inductor has to discharge, the
current flows through the free-wheeling Schottky diode
to the output. In this case, the inductor discharge rate is
(where VD is the diode forward voltage);
(
V
+ V
)
OUT
D
−
L
The total off time can be calculated as;
1− D
fsw
TOFF
=
Figure 5. Discontinuous Operation
Discontinuous mode of operation has the advantage
over full PWM in that at light loads, the MIC4782 will skip
pulses as necessary, reducing gate drive losses,
drastically improving light load efficiency.
Efficiency Considerations
Calculating the efficiency is as simple as measuring
power out and dividing it by the power in;
P
OUT
Efficiency =
×100
P
IN
Where input power (PIN) is;
P
= V ×I
IN
IN
IN
Figure 4. Off-Time
and output power (POUT) is calculated as;
Discontinuous Operation
P
= V ×I
OUT
OUT
OUT
Discontinuous operation is when the inductor current
discharges to zero during the off cycle. Figure 5
demonstrates the switch voltage and inductor currents
during discontinuous operation.
The Efficiency of the MIC4782 is determined by several
factors.
•
•
•
•
RDSON (Internal P-channel Resistance)
Diode conduction losses
Inductor Conduction losses
Switching losses
When the inductor current (IL) has completely
discharged, the voltage on the switch node rings at the
frequency determined by the parasitic capacitance and
the inductor value. In Figure 5, it is drawn as a DC
voltage, but to see actual operation (with ringing) refer to
the functional characteristics.
RDSON losses are caused by the current flowing through
the high side P-Channel MOSFET. The amount of power
loss can be approximated by;
2
P
= R
×I
× D
SW
DSON
OUT
Where D is the duty cycle.
Since the MIC4782 uses an internal P-Channel
MOSFET, RDSON losses are inversely proportional to
supply voltage. Higher supply voltage yields a higher
gate to source voltage, reducing the RDSON, reducing the
MOSFET conduction losses. A graph showing typical
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MIC4782
RDSON vs. input supply voltage can be found in the typical
characteristics section of this datasheet.
Switching losses occur twice each cycle, when the
switch turns on and when the switch turns off. This is
caused by a non-ideal world where switching transitions
are not instantaneous, and neither are currents. Figure 6
demonstrates how switching losses due to the
transitions dissipate power in the switch.
Diode conduction losses occur due to the forward
voltage drop (VF) and the output current. Diode power
losses can be approximated as follows;
P
= V ×I ×
OUT
(
1− D
)
D
F
For this reason, the Schottky diode is the rectifier of
choice. Using the lowest forward voltage drop will help
reduce diode conduction losses, and improve efficiency.
Duty cycle, or the ratio of output voltage-to-input voltage,
determines whether the dominant factor in conduction
losses will be the internal MOSFET or the Schottky
diode. Higher duty cycles place the power losses on the
high side switch, and lower duty cycles place the power
losses on the Schottky diode.
Inductor conduction losses (PL) can be calculated by
multiplying the DC resistance (DCR) times the square of
the output current;
Figure 6. Switching Transition Losses
Normally, when the switch is on, the voltage across the
switch is low (virtually zero) and the current through the
switch is high. This equates to low power dissipation.
When the switch is off, voltage across the switch is high
and the current is zero, again with power dissipation
being low. During the transitions, the voltage across the
switch (VS-D) and the current through the switch (IS-D) are
at middle, causing the transition to be the highest
instantaneous power point. During continuous mode,
these losses are the highest. Also, with higher load
currents, these losses are higher. For discontinuous
operation, the transition losses only occur during the “off”
transition since the “on” transitions there is no current
flow through the inductor.
2
P = DCR ×I
L
OUT
Also, be aware that there are additional core losses
associated with switching current in an inductor. Since
most inductor manufacturers do not give data on the
type of material used, approximating core losses
becomes very difficult, so verify inductor temperature
rise.
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MIC4782
minimize switching noise.
Component Selection
Input Capacitor
Feedback Resistors
A 10µF ceramic is recommended on each VIN pin for
bypassing. X5R or X7R dielectrics are recommended for
the input capacitor. Y5V dielectrics lose most of their
capacitance over temperature and are therefore, not
recommended. Also, tantalum and electrolytic capacitors
alone are not recommended due to their reduced RMS
current handling, reliability, and ESR increases.
The feedback resistor set the output voltage by dividing
down the output and sending it to the feedback pin. The
feedback voltage is 0.6V. Calculating the set output
voltage is as follows;
R1
R2
⎛
⎜
⎞
V
= V
+ 1
⎟
OUT
FB
⎝
⎠
An additional 0.1µF is recommended close to the VIN
and PGND pins for high frequency filtering. Smaller case
size capacitors are recommended due to their lower
ESR and ESL. Please refer to layout recommendation
for proper layout of the input capacitor.
Where R1 is the resistor from VOUT to FB and R2 is the
resistor from FB-to-GND. The recommended feedback
resistor values for common output voltages are available
in the bill of materials on page 19 of this data sheet.
Although the range of resistance for the FB resistors is
very wide, R1 is recommended to be 10Kꢀ. This
minimizes the parasitic capacitance effect of the FB
node.
Output Capacitor
The MIC4782 is designed to be stable with a 4.7µF
output capacitor. X5R or X7R dielectrics are
recommended for the output capacitor. Y5V dielectrics
lose most of their capacitance over temperature and are
therefore not recommended.
Feedforward Capacitor (CFF)
A capacitor across the resistor from the output to the
feedback pin (R1) is recommended for most designs.
This capacitor can give a boost to phase margin and
increase the bandwidth for transient response. Also,
large values of feedforward capacitance can slow down
the turn-on characteristics, reducing inrush current. For
maximum phase boost, CFF can be calculated as follows;
In addition to a 4.7µF or larger value output capacitor, a
small 0.1µF is recommended close to the load for high
frequency filtering. Smaller case size capacitors are
recommended due to there lower equivalent series ESR
and ESL.
The MIC4782 utilizes type III voltage mode internal
compensation and utilizes an internal zero to
compensate for the double pole roll off of the LC filter.
1
CFF
=
2π × 200kHz × R1
Large values of feedforward capacitance may introduce
negative FB pin voltage during load shorting, which will
cause latch-off. In that case, a Schottky diode from FB
pin to the ground is recommended.
Inductor Selection
The MIC4782 is designed for use with a 1µH inductor.
Proper selection should ensure the inductor can handle
the maximum average and peak currents required by the
load. 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% to 20%
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.
Bias Filter
A small 10ꢀ resistor is recommended from the input
supply to the bias pin along with a small 0.1µF ceramic
capacitor from bias-to-ground. This will bypass the high
frequency noise generated by the violent switching of
high currents from reaching the internal reference and
control circuitry. Tantalum and electrolytic capacitors are
not recommended for the bias, these types of capacitors
lose their ability to filter at high frequencies.
Diode Selection
Voltage Derating of Ceramic Capacitors
Since the MIC4782 is non-synchronous, a free-wheeling
diode is required for proper operation. A Schottky diode
is recommended due to the low forward voltage drop
and their fast reverse recovery time. The diode should
be rated to be able to handle the average output current.
Also, the reverse voltage rating of the diode should
exceed the maximum input voltage. The lower the
forward voltage drop of the diode the better the
efficiency. Please refer to the layout recommendation to
The capacitance of ceramic capacitors drops at high
voltage. Figure 7 shows typical voltage derating curves
of X5R 6.3V ceramic capacitors. At half of the rating
voltage and room temperature, the capacitance of 0603
X5R capacitors can drop about 30%, while the 0805
package only drops by 5%. Therefore, 0805 package
ceramic capacitors are preferred if the application
voltage is close to half of the capacitor rating voltage or
13
M9999-081709-D
August 2009
Micrel, Inc.
higher.
MIC4782
20
0
-20
-40
-60
-80
-100
0603 X5R 6.3V Ceramic Capacitor
0805 X5R 6.3V Ceramic Capacitor
0
1
2
3
4
5
6
7
VOLT AGE APPLIED (V)
Figure 7. Voltage Derating of Ceramic Capacitors
14
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August 2009
Micrel, Inc.
MIC4782
Bode Plot
Vin=3.6V Vout=1.8V Iout=2A
Loop Stability and Bode Analysis
60
50
40
30
20
10
0
210
175
140
105
70
Bode analysis is an excellent way to measure small
signal stability and loop response in power supply
designs. Bode analysis monitors gain and phase of a
control loop. This is done by breaking the feedback loop
and injecting a signal into the feedback node and
comparing the injected signal to the output signal of the
control loop. This will require a network analyzer to
sweep the frequency and compare the injected signal to
the output signal. The most common method of injection
is the use of transformer. Figure 8 demonstrates how a
transformer is used to inject a signal into the feedback
network.
35
0
-10
-20
-30
-35
-70
-105
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
FREQUENCY (Hz)
Typically for 3.6VIN and 1.8VOUT at 2A;
•
•
Phase Margin = 77.8 Degrees
GBW = 229KHz
Being that the MIC4782 is non-synchronous; the
regulator only has the ability to source current. This
means that the regulator has to rely on the load to be
able to sink current. This causes a non-linear response
at light loads. The following plot shows the effects of the
pole created by the nonlinearity of the output drive
during light load (discontinuous) conditions.
Figure 8. Transformer Injection
Bode Plot
Vin=3.6V Vout=1.8V Iout=0.1A
60
50
40
30
20
10
0
210
175
140
105
70
A 50ꢀ resistor allows impedance matching from the
network analyzer source. This method allows the DC
loop to maintain regulation and allow the network
analyzer to insert an AC signal on top of the DC voltage.
The network analyzer will then sweep the source while
monitoring A and R for an A/R measurement.
35
0
The following Bode analysis show the small signal loop
stability of the MIC4782, it utilizes type III compensation.
This is a dominant low frequency pole, followed by two
zeros and finally the double pole of the inductor
capacitor filter, creating a final 20dB/decade roll off.
Bode analysis gives us a few important data points;
speed of response (Gain Bandwidth or GBW) and loop
stability. Loop speed or GBW determines the response
time to a load transient. Faster response times yield
smaller voltage deviations to load steps.
-10
-20
-30
-35
-70
-105
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
FREQUENCY (Hz)
3.6VIN, 1.8VOUT IOUT = 0.1A;
•
•
Phase Margin=89.9 Degrees
GBW= 43.7kHz
Instability in a control loop occurs when there is gain and
positive feedback. Phase margin is the measure of how
stable the given system is. It is measured by determining
how far the phase is from crossing zero when the gain is
equal to 1 (0dB).
Feed Forward Capacitor
The feedback resistors are a gain reduction block in the
overall system response of the regulator. By placing a
capacitor from the output to the feedback pin, high
frequency signal can bypass the resistor divider, causing
a gain increase up to unity gain.
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M9999-081709-D
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Micrel, Inc.
MIC4782
Max. Amount of Phase Boost
Obtainable Using Cff vs. Output
Voltage
Gain and Phase
vs. Frequency
0
-5
35
30
25
20
15
10
5
60
50
40
30
20
10
0
-10
-15
-20
0
100
1000
10000
100000
1000000
0
1
2
3
4
5
FREQUENCY (Hz)
OUTPUT VOLTAGE (V)
By looking at the graph, phase margin can be affected to
a greater degree with higher output voltages.
The graph above shows the effects on the gain and
phase of the system caused by feedback resistors and a
feedforward capacitor. The maximum amount of phase
boost achievable with a feedforward capacitor is
graphed below.
16
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Micrel, Inc.
MIC4782
Ripple Measurements
To properly measure ripple on either input or output of a
switching regulator, a proper ring in tip measurement is
required. Standard oscilloscope probes come with a
grounding clip, or a long wire with an alligator clip.
Unfortunately, for high frequency measurements, this
ground clip can pick-up high frequency noise and
erroneously inject it into the measured output ripple.
The standard evaluation board accommodates a home
made version by providing probe points for both the
input and output supplies and their respective grounds.
This requires the removing of the oscilloscope probe
sheath and ground clip from a standard oscilloscope
probe and wrapping a non-shielded bus wire around the
oscilloscope probe. If there does not happen to be any
non-shielded bus wire immediately available, then the
leads from axial resistors will work. By maintaining the
shortest possible ground lengths on the oscilloscope
probe, true ripple measurements can be obtained.
17
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August 2009
Micrel, Inc.
MIC4782
power connection.
Inductor
PCB Layout Guideline
Warning!!! To minimize EMI and output noise, follow
these layout recommendations.
•
•
•
•
Keep the inductor connection to the switch node
(SW) short.
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.
Do not route any digital lines underneath or close to
the inductor.
Keep the switch node (SW) away from the feedback
(FB) pin.
The following guidelines should be followed to insure
proper operation of the MIC4782 converter.
To minimize noise, place a ground plane underneath
the inductor.
IC
•
•
•
•
•
Place the IC and MOSFETs close to the point of
load (POL).
Output Capacitor
•
Use a wide trace to connect the output capacitor
ground terminal to the input capacitor ground
terminal.
Use fat traces to route the input and output power
lines.
The exposed pad (EP) on the bottom of the IC must
be connected to the ground.
•
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.
Use several vias to connect the EP to the ground
plane, layer 2.
Signal and power grounds should be kept separate
and connected at only one location.
•
•
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.
Input Capacitor
•
•
Place the input capacitor next.
If 0603 package ceramic output capacitors are used,
then make sure that it has enough capacitance at
the desired output voltage. Please refer to the
“Voltage Derating of Ceramic Capacitors” subsection
in “Component Selection” of this data sheet for more
details.
Place the input capacitors on the same side of the
board and as close to the IC as possible.
•
•
Keep both the VIN and PGND connections short.
Place several vias to the ground plane close to the
input capacitor ground terminal, but not between the
input capacitors and IC pins.
Diode
•
•
Use either X7R or X5R dielectric input capacitors.
Do not use Y5V or Z5U type capacitors.
•
Place the Schottky diode on the same side of the
board as the IC and input capacitor.
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.
•
The connection from the Schottky diode’s Anode to
the input capacitors ground terminal must be as
short as possible.
•
•
•
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%.
•
The diode’s Cathode connection to the switch node
(SW) must be keep as short as possible.
RC Snubber
Place the RC snubber on the same side of the board
and as close to the IC as possible.
In “Hot-Plug” applications, a Tantalum or Electrolytic
bypass capacitor must be used to limit the over-
voltage spike seen on the input supply with power is
suddenly applied.
•
An additional Tantalum or Electrolytic bypass input
capacitor of 22µF or higher is required at the input
18
M9999-081709-D
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Micrel, Inc.
MIC4782
Bill of Materials
MIC4782YML Schematic for 2A Output
Item
Part Number
Manufacturer
Description
Qty
C11,C12
C21,C22
C15,C25
C13(7),C23(7)
C14,C24
C16,C26,C7
C18,C28
D1,D2
0805ZD106MAT2A
AVX(1)
10µF, Ceramic Capacitor, X5R, 0805, 10V
6
VJ0603A681KXXCW
VJ0603A820KXXCW
Vishay(2)
Vishay(2)
680pF, Ceramic Capacitor, NP0, 0603, 25V
82pF, Ceramic Capacitor, NP0, 0603, 25V
2
2
VJ0603Y104KXXAT
Vishay(2)
0.1µF, Ceramic, Capacitor, X7R, 0603, 25V
5
SS2P3L
Vishay(2)
Vishay(2)
Diodes(3)
Vishay(2)
TDK(4)
2A Schottky, 30V
2
SSA23L
B230A
L1,L2
IHLP2525AH-01 1R0
RLF7030-1R0 N
HCP0703-1R0
1µH Inductor, 17.5mꢀ 6.86mm(L) x 6.47mm(W) x 1.8mm(H)
1µH Inductor, 8.8mꢀ 7.3mm(L) x 6.8mm(W) x 3.2mm(H)
1µH Inductor, 10mꢀ 7.3mm(L) x 7.0mm(W) x 3.0mm(H)
10Kꢀ, 1%, 0603, resistor
2
2
COOPER(5)
Vishay(2)
R11,R12
R12,R22
CRCW060310K0FKXX
CRCW06033K16FKXX
CRCW06034K99FKXX
CRCW06036K65FKXX
CRCW060310K0FKXX
3.16kꢀ,1%, 0603 For 2.5VOUT
4.99kꢀ, 1%, 0603 For 1.8 VOUT
Vishay(2)
6.65kꢀ, 1%, 0603 For 1.5 VOUT
2
10kꢀ, 1%, 0603 For 1.2 VOUT
CRCW060315K0FKXX
15kꢀ, 1%, 0603 For 1.0 VOUT
19
M9999-081709-D
August 2009
Micrel, Inc.
MIC4782
Item
Part Number
Manufacturer
Description
Qty
R13(7),
R23(7)
CRCW06032R70FKXX
CRCW060349K9FKXX
CRCW060310R0FKXX
MIC4782YML
Vishay(2)
Vishay(2)
Vishay(2)
2.7ꢀ, 1%, 0603, resistor
2
2
1
1
R14, R24
R5
49.9kꢀ, 1%, 0603, resistor
10ꢀ, 1%, 0603, resistor
U1
Micrel, Inc.(6)
Dual, 2A, 1.8MHz, Integrated Switch Buck Regulator
Notes:
1. AVX: www.avx.com
2. Vishay: www.vishay.com
3. Diode: www.diodes.com
4. TDK: www.tdk.com
5. Cooper: www.cooperbussmann.com
6. Micrel, Inc: www.micrel.com
7. Only for ultra-low noise applications.
20
M9999-081709-D
August 2009
Micrel, Inc.
MIC4782
MIC4782YML Layout Recommendation: 2A Evaluation Board
TOP Layer
Mid-Layer 1
21
M9999-081709-D
August 2009
Micrel, Inc.
MIC4782
Mid-Layer 2
Bottom Layer
22
M9999-081709-D
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Micrel, Inc.
MIC4782
Package Information
16-Pin 3mm x 3mm 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.
23
M9999-081709-D
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