MIC2171
100kHz 2.5A Switching Regulator
General Description
The MIC2171 is a complete 100kHz SMPS current-mode
controller with an internal 65V 2.5A power switch.
Although primarily intended for voltage step-up applica-
tions, the floating switch architecture of the MIC2171
makes it practical for step-down, inverting, and Cuk config-
urations as well as isolated topologies.
Operating from 3V to 40V, the MIC2171 draws only 7mA
of quiescent current, making it attractive for battery
operated supplies.
The MIC2171 is available in a 5-pin TO-220 or TO-263 for
–40°C to +85°C operation.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Features
•
•
•
•
•
•
•
•
•
•
2.5A, 65V internal switch rating
3V to 40V input voltage range
Current-mode operation, 2.5A peak
Internal cycle-by-cycle current limit
Thermal shutdown
Twice the frequency of the LM2577
Low external parts count
Operates in most switching topologies
7mA quiescent current (operating)
Fits LT1171/LM2577 TO-220 and TO-263 sockets
Applications
•
•
•
•
Laptop/palmtop computers
Battery operated equipment
Hand-held instruments
Off-line converter up to 50W(requires external power
switch)
•
Pre-driver for higher power capability
___________________________________________________________________________________________________________
Typical Application
+5V
(4.75V min.)
V
IN
4V to 6V
C1
47µF
IN
SW
MIC2171
R3
1k
COMP
GND
C2
1µF
FB
V
OU T
5V, 0.5A
R1
C4
3.74k
470µF 1%
L1
15µH
IN
SW
D1
C1*
47µF
V
OU T
+12V, 0.25A
R1
10.7k
1%
R2
C2
1.24k
470µF 1%
T1
R4*
C3*
D1*
1:1.25
L
P R I
= 12µH
D2
1N5818
MIC2171
R3
1k
COMP
GND
C3
1µF
FB
1N5822
R2
1.24k
1%
* Locate near MIC2171 when supply leads > 2”
* Optional voltage clipper (may be req’d if T1 leakage inductance too high)
Figure 1. MIC2171 5V to 12V Boost Converter
Figure 2. MIC2171 5VFlyback Converter
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 2007
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M9999-051107
Micrel, Inc.
MIC2171
Ordering Information
Part Number
Standard
MIC2171BT
MIC2171BU
RoHS Compliant*
MIC2171WT
MIC2171WU
Temperature Range
–40° to +85°C
–40° to +85°C
Package
5-Pin TO-220
5-Pin TO-263
*RoHS compliant with "high-melting solder" exemption.
Pin Configuration
5
4
3
2
1
Tab GND
5-Pin TO-220 (T)
IN
SW
GND
FB
COMP
Tab GND
5
4
3
2
1
IN
SW
GND
FB
COMP
5-Pin TO-263 (U)
Pin Description
Pin Number
1
Pin Name
COMP
Pin Function
Frequency Compensation: Output of transconductance-type error amplifier.
Primary function is for loop stabilization. Can also be used for output voltage
soft-start and current limit tailoring.
Feedback: Inverting input of error amplifier. Connect to external resistive divider
to set power supply output voltage.
Ground: Connect directly to the input filter capacitor for proper operation (see
applications info).
Power Switch Collector: Collector of NPN switch. Connect to external inductor
or input voltage depending on circuit topology.
Supply Voltage: 3.0V to 40V
2
3
4
5
FB
GND
SW
IN
May 2007
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M9999-051107
Micrel, Inc.
MIC2171
Absolute Maximum Ratings
Supply Voltage (V
IN
) .......................................................40V
Switch Voltage (V
SW
)......................................................65V
Feedback Voltage (transient, 1ms) (V
FB
) .....................±15V
Lead Temperature (soldering, 10 sec.)...................... 300°C
Storage Temperature (T
s
) .........................–65°C to +150°C
ESD Rating
(1)
Operating Ratings
Operating Temperature Range ................... –40°C to +85°C
Junction Temperature (T
J
) ........................ –55°C to +150°C
Thermal Resistance
TO-220-5 (θ
JA
)
(2)
...............................................45°C/W
TO-263-5 (θ
JA
)
(3)
................................................45°C/W
Electrical Characteristics
V
IN
= 5V; T
A
= 25°C,
bold
values indicate –40°C< T
A
< +85°C, unless noted.
Parameter
Reference Section
Feedback Voltage (V
FB
)
Feedback Voltage
Line Regulation
Feedback Bias Current (I
FB
)
Error Amplifier Section
Transconductance (g
m
)
Voltage Gain (A
V
)
Output Current
Output Swing
Compensation Pin Threshold
Output Switch Section
ON Resistance
Current Limit
I
SW
= 2A, V
FB
= 0.8V
Duty Cycle = 50%, T
J
≥
25°C
Duty Cycle = 50%, T
J
< 25°C
Duty Cycle = 80%,
Note 4
3V
≤
V
IN
≤
40V
I
SW
= 5mA
2.5
2.5
2.5
65
0.37
3.6
4.0
3.0
75
0.50
0.55
5.0
5.5
5.0
Ω
Ω
A
A
A
V
∆I
COMP
= ±25µA
0.9V
≤
V
COMP
≤
1.4V
V
COMP
= 1.5V
High Clamp, V
FB
= 1V
Low Clamp, V
FB
= 1.5V
Duty Cycle = 0
3.0
2.4
400
125
100
1.8
0.25
0.8
0.6
3.9
800
175
2.1
0.35
0.9
6.0
7.0
2000
350
400
2.3
0.52
1.08
1.25
µA/mV
µA/mV
V/V
µA
µA
V
V
V
V
V
COMP
= 1.24V
3V
≤
V
IN
≤
40V
V
COMP
= 1.24V
V
FB
= 1.24V
1.220
1.214
1.240
0.6
310
750
1100
1.264
1.274
V
V
%/V
nA
nA
Condition
Min
Typ
Max
Units
Breakdown Voltage (BV)
Oscillator Section
Frequency (f
O
)
Duty Cycle [δ(max)]
Input Supply Voltage Section
Minimum Operating Voltage
Quiescent Current (I
Q
)
Supply Current Increase (∆I
IN
)
Notes:
88
85
80
100
90
2.7
7
9
112
115
95
3.0
9
20
kHz
kHz
%
V
mA
mA
3V
≤
V
IN
≤
40V, V
COMP
= 0.6V, I
SW
= 0
∆I
SW
= 2A, V
COMP
= 1.5V, during switch on-time
1. Devices are ESD sensitive. Handling precautions recommended.
2. Mounted vertically, no external heat sink, 1/4 inch leads soldered to PC board containing approximately 4 inch squared copper area surrounding
leads.
3. All ground leads soldered to approximately 2 inches squared of horizontal PC board copper area.
4. For duty cycles (δ) between 50% and 95%, minimum guaranteed switch current is I
CL
= 1.66 (2-δ) Amp (Pk).
May 2007
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M9999-051107
Micrel, Inc.
MIC2171
Typical Characteristics
2.9
Minimum Operating Voltage (V)
2.8
2.7
2.6
Switch Current = 2A
2.5
2.4
2.3
-100
-50
0
50
100
Temperature (°C)
150
Minimum
Operating Voltage
Feedback Bias Current (nA)
Feedback Voltage Change (mV)
800
700
600
500
400
300
200
100
0
-100
Feedback Bias Current
5
4
3
2
1
0
-1
-2
-3
-4
-5
Feedback Voltage
Line Regulation
T = 125°C
J
TJ = 25°C
T = -40°C
J
0
10
20
30
V
IN
Operating (V)
40
-50
0
50
100
Temperature (°C)
150
Supply Current (mA)
D.C . = 90%
Supply Current (mA)
13
12
11
10
9
8
7
6
5
Average Supply Current (mA)
15
14
Supply Current
IS W = 0
50
40
30
20
Supply Current
10
9
8
7
6
5
4
3
Supply Current
V
C OMP
= 0.6V
δ
= 90%
D.C . = 50%
D.C . = 0%
δ
= 50%
10
0
0
10
20
30
V
IN
Operating Voltage (V)
40
0
1
2
3
Switch Current (A)
4
2
1
0
-100
-50
0
50
100
Temperature(°C)
150
1.6
1.4
Switch ON Voltage (V)
Switch On-Voltage
120
110
100
90
80
70
Oscillator Frequency
8
Current Limit
1.0
0.8
0.6
0.4
0.2
0
0
T = –40°C
J
Switch Current (A)
Frequency (kHz)
1.2
T = 25°C
J
6
–40°C
25°C
4
T = 125°C
J
2
125°C
1
2
Switch Current (A)
3
60
-50
0
50
100
Temperature(°C)
150
0
0
20
40
60
80
Duty Cycle (%)
100
Transconductance (µA/mV)
Transconductance (µS)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-100
Error Amplifier Gain
7000
6000
Error Amplifier Gain
-30
0
30
Phase Shift (°)
60
90
120
150
180
Error Amplifier Phase
5000
4000
3000
2000
1000
0
1
10
100
1000
Frequency (kHz)
10000
-50
0
50
100
Temperature(°C)
150
210
1
10
100
1000
Frequency (kHz)
10000
May 2007
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M9999-051107
Micrel, Inc.
MIC2171
Functional Diagram
IN
Reg.
2.3V
100kHz
Osc.
D1
Anti-Sat.
Logic
Driver
Q1
SW
FB
Error
1.24V Amp.
Ref.
Com
-
parator
Current
Amp.
COMP
GND
Functional Description
Refer to “Block Diagram MIC2171”.
Internal Power
The MIC2171 operates when V
IN
is
≥
2.6V. An internal
2.3V regulator supplies biasing to all internal circuitry
including a precision 1.24V band gap reference.
PWM Operation
The 100kHz oscillator generates a signal with a duty
cycle of approximately 90%. The current-mode
comparator output is used to reduce the duty cycle when
the current amplifier output voltage exceeds the error
amplifier output voltage. The resulting PWM signal
controls a driver which supplies base current to output
transistor Q1.
Current-Mode Advantages
The MIC2171 operates in current mode rather than
voltage mode. There are three distinct advantages to
this technique. Feedback loop compensation is greatly
simplified because inductor current sensing removes a
pole from the closed loop response. Inherent cycle-by-
cycle current limiting greatly improves the power switch
reliability and provides automatic output current limiting.
Finally, current-mode operation provides automatic input
voltage feed forward which prevents instantaneous input
voltage changes from disturbing the output voltage
setting.
Anti-Saturation
The anti-saturation diode (D1) increases the usable duty
cycle range of the MIC2171 by eliminating the base to
collector stored charge which would delay Q1’s turnoff.
Compensation
Loop stability compensation of the MIC2171 can be
accomplished by connecting an appropriate network
from either COMP to circuit ground (see “Typical
Applications”) or COMP to FB.
The error amplifier output (COMP) is also useful for soft
start and current limiting. Because the error amplifier
output is a transconductance type, the output impedance
is relatively high which means the output voltage can be
easily clamped or adjusted externally.
May 2007
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M9999-051107
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