MIC2172/3172
Micrel
MIC2172/3172
100kHz 1.25A Switching Regulators
Preliminary Information
General Description
The MIC2172 and MIC3172 are complete 100kHz SMPS
current-mode controllers with internal 65V 1.25A power
switches. The MIC2172 features external frequency syn-
chronization or frequency adjustment, while the MIC3172
features an enable/shutdown control input.
Although primarily intended for voltage step-up applications,
the floating switch architecture of the MIC2172/3172 makes
it practical for step-down, inverting, and Cuk configurations
as well as isolated topologies.
Operating from 3V to 40V, the MIC2172/3172 draws only
7mA of quiescent current making it attractive for battery
operated supplies.
The MIC3172 is for applications that require on/off control of
the regulator. The MIC3172 is externally shutdown by
applying a TTL low signal to EN (enable). When disabled, the
MIC3172 draws only leakage current (typically less than
1µA). EN must be high for normal operation. For applications
not requiring control, EN must be tied to V
IN
or TTL high.
The MIC2172 is for applications requiring two or more SMPS
regulators that operate from the same input supply. The
MIC2172 features a SYNC input which allows locking of its
internal oscillator to an external reference. This makes it
possible to avoid the audible beat frequencies that result from
the unequal oscillator frequencies of independent SMPS
regulators.
A reference signal can be supplied by one MIC2172 desig-
nated as a master. To insure locking of the slave’s oscillators,
the reference oscillator frequency must be higher than the
slave’s. The master MIC2172’s oscillator frequency is in-
creased up to 135kHz by connecting a resistor from SYNC to
ground (see applications information).
The MIC2172/3172 is available in an 8-pin plastic DIP or
SOIC for –40°C to +85°C operation.
Features
•
•
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•
•
•
•
•
•
•
•
•
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1.25A, 65V internal switch rating
3V to 40V input voltage range
Current-mode operation
Internal cycle-by-cycle current limit
Thermal shutdown
Low external parts count
Operates in most switching topologies
7mA quiescent current (operating)
<1µA quiescent current, shutdown mode (MIC3172)
TTL shutdown compatibility (MIC3172)
External frequency synchronization (MIC2172)
External frequency trim (MIC2172)
Fits most LT1172 sockets (see applications info)
4
Applications
Laptop/palmtop computers
Toys
Hand-held instruments
Off-line converter up to 50W
(requires external power switch)
• Predriver for higher power capability
• Master/slave configurations (MIC2172)
Typical Applications
+5V
(4.75V min.)
L1
27µH
V
IN
N/C
SYNC
MIC2172
R3
1k
COMP GND
FB
P1 P2 S
C3
1µF
V
SW
1N5822
D1
V
IN
4V to 6V
T1
R4*
C3*
D2
1N5818
C4
470µF
V
OUT
5V, 0.25A
R1
3.74k
1%
C1*
22µF
V
OUT
+12V, 0.14A
R1
10.7k
1%
R2
C2
1.24k
470µF 1%
Enable
Shutdown
C1
22µF
V
IN
EN
MIC3172
D1*
V
SW
1:1.25
L
PRI
= 100µH
R3
1k
COMP GND
FB
P1 P2 S
C2
1µF
R2
1.24k
1%
* Locate near MIC2172 when supply leads > 2"
* Optional voltage clipper (may be req’d if T1 leakage inductance too high)
Figure 1.
MIC2172 5V to 12V Boost Converter
Figure 2.
MIC3172 5V Flyback Converter
1997
4-13
MIC2172/3172
Micrel
Ordering Information
Part Number
MIC2172BN
MIC2172BM
MIC3172BN
MIC3172BM
Temperature Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
8-pin plastic DIP
8-lead SOIC
8-pin plastic DIP
8-lead SOIC
Pin Configuration
MIC2172*/3172
†
S GND 1
COMP 2
FB 3
*SYNC/
†
EN 4
8
7
P GND 1
V
SW
MIC2172*/3172
†
S GND 1
COMP 2
FB 3
*SYNC/
†
EN 4
8 P GND 1
7 V
SW
6 P GND 2
5 V
I N
6 P GND 2
5 V
I N
8-lead DIP (N)
8-lead SOIC (M)
Pin Description
Pin Number
1
Pin Name
S GND
Pin Function
Signal Ground: Internal analog circuit ground. Connect directly to the input
filter capacitor for proper operation (see applications info). Keep separate
from power grounds.
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.
Synchronization/Frequency Adjust: Capacitively coupled input signal greater
than device’s free running frequency (up to 135kHz) will lock device’s
oscillator on falling edge. Oscillator frequency can be trimmed up to 135kHz
by adding a resistor to ground. If unused, pin must float (no connection).
Enable: Apply TTL high or connect to V
IN
to enable the regulator. Apply
TTL low or connect to ground to disable the regulator. Device draws only
leakage current (<1µA) when disabled.
Supply Voltage: 3.0V to 40V
Power Ground #2: One of two NPN power switch emitters with 0.3Ω current
sense resistor in series. Required. Connect to external inductor or input
voltage ground depending on circuit topology.
Power Switch Collector: Collector of NPN switch. Connect to external
inductor or input voltage depending on circuit topology.
Power Ground #1: One of two NPN power switch emitters with 0.3Ω current
sense resistor in series. Optional. For maximum power capability connect
to P GND 2. Floating pin reduces current limit by a factor of two.
2
COMP
3
4 (MIC2172)
FB
SYNC
4 (MIC3172)
EN
5
6
V
IN
P GND 2
7
8
V
SW
P GND 1
4-14
1997
MIC2172/3172
Micrel
Absolute Maximum Ratings MIC2172
Input Voltage ................................................................. 40V
Switch Voltage .............................................................. 65V
Sync Current .............................................................. 50mA
Feedback Voltage (Transient, 1ms) ...........................
±15V
Operating Temperature Range
8-pin PDIP ................................................. –40 to +85°C
8-pin SOIC ................................................ –40 to +85°C
Junction Temperature .............................. –55°C to +150°C
Thermal Resistance
θ
JA
8-pin PDIP .................................................130°C/W
θ
JA
8-pin SOIC .................................................120°C/W
Storage Temperature ............................... –65°C to +150°C
Soldering (10 sec.) .................................................. +300°C
Electrical Characteristics MIC2172
Parameter
Reference Section
Feedback Voltage (V
FB
)
Feedback Voltage
Line Regulation
Feedback Bias Current (I
FB
)
Error Amplifier Section
Transconductance (∆I
COMP
/∆V
FB
)
∆I
COMP
=
±25µA
Voltage Gain (∆V
COMP
/∆V
FB
)
Output Current
Output Swing
Compensation Pin
Threshold
Output Switch Section
ON Resistance
Current Limit
3V
≤
V
IN
≤
40V
Conditions
Pin 2 tied to pin 3
Note 1. Unless otherwise specified, V
IN
= 5V.
Min
Typ
Max
Units
1.220
1.214
1.240
1.264
1.274
0.03
V
V
%/V
nA
nA
310
750
1100
4
3.0
2.4
500
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
0.9V
≤
V
COMP
≤
1.4V
V
COMP
= 1.5V
High Clamp, V
FB
= 1V
Low Clamp, V
FB
= 1.5V
Duty Cycle = 0
I
SW
= 1A, V
FB
= 0.8V
Duty Cycle = 50%, T
J
≥
25°C
Duty Cycle = 50%, T
J
< 25°C
Duty Cycle = 80%
Note 2
3V
≤
V
IN
≤
40V
I
SW
= 5mA
1.25
1.25
1
65
0.76
1
1.1
3
3.5
2.5
Ω
Ω
A
A
A
V
Breakdown Voltage (BV)
75
1997
4-15
MIC2172/3172
Parameter
Oscillator Section
Frequency (f
O
)
Duty Cycle [δ(max)]
Sync Coupling Capacitor
Required for Frequency Lock
Peak-to-Peak Voltage
Required for Frequency Lock
Input Supply Voltage Section
Minimum Operating Voltage
Quiescent Current (I
Q
)
Supply Current Increase (∆I
IN
)
Note 1
Note 2
Micrel
Conditions
Min
Typ
Max
Units
88
85
80
V
PP
= 3.0V
V
PP
= 40V
C
COUPLING
= 12pF
22
2.2
2.2
100
89
51
4.7
12
112
115
95
120
10
30
kHz
kHz
%
pF
pF
V
2.7
3V
≤
V
IN
≤
40V, V
COMP
= 0.6V, I
SW
= 0
∆I
SW
= 1A, V
COMP
= 1.5V
7
9
3.0
9
20
V
mA
mA
Bold
type denotes specifications applicable to the full operating temperature range.
Devices are ESD sensitive. Handling precautions required.
For duty cycles (δ) between 50% and 95%, minimum guaranteed switch current is given by I
CL
= 0.833 (2-δ) for the MIC3172.
Absolute Maximum Ratings MIC3172
Input Voltage ................................................................. 40V
Switch Voltage .............................................................. 65V
Enable Voltage .............................................................. 40V
Feedback Voltage (Transient, 1ms) ...........................
±15V
Operating Temperature Range
8-pin PDIP ................................................. –40 to +85°C
8-pin SOIC ................................................ –40 to +85°C
8-pin CerDIP ........................................... –55 to +125°C
Junction Temperature ................................ –55°C to 150°C
Thermal Resistance
θ
JA
8-pin PDIP .................................................130°C/W
θ
JA
8-pin SOIC .................................................120°C/W
θ
JA
8-pin CerDIP .............................................. 100°C/W
Storage Temperature ................................. –65°C to 150°C
Soldering (10 sec.) .................................................... 300°C
Electrical Characteristics MIC3172
Parameter
Reference Section
Feedback Voltage (V
FB
)
Feedback Voltage
Line Regulation
Feedback Bias Current (I
FB
)
3V
≤
V
IN
≤
40V
Conditions
Pin 2 tied to pin 3
Note 1. Unless otherwise specified, V
IN
= 5V.
Min
Typ
Max
Units
1.224
1.214
1.240
0.07
310
1.264
1.274
V
V
%/V
750
1100
nA
nA
4-16
1997
MIC2172/3172
Parameter
Error Amplifier Section
Transconductance (∆I
COMP
/∆V
FB
)
∆I
COMP
=
±25µA
Voltage Gain (∆V
COMP
/∆V
FB
)
Output Current
Output Swing
Compensation Pin
Threshold
Output Switch Section
ON Resistance
Current Limit
I
SW
= 1A, V
FB
= 0.8V
Duty Cycle = 50%, T
J
≥
25°C
Duty Cycle = 50%, T
J
< 25°C
Duty Cycle = 80%
Note 2
3V
≤
V
IN
≤
40V
I
SW
= 5mA
1.25
1.25
1
65
75
0.76
1
1.1
3
3.5
2.5
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
500
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
Conditions
Min
Typ
Max
Micrel
Units
µA/mV
µA/mV
V/V
µA
µA
V
V
V
V
Ω
Ω
A
A
A
V
Breakdown Voltage (BV)
Oscillator Section
Frequency (f
O
)
Duty Cycle [δ(max)]
88
85
80
100
89
112
115
95
kHz
kHz
%
4
Input Supply Voltage Section and Enable Section
Minimum Operating Voltage
Quiescent Current (I
Q
)
Quiescent Current Increase (∆I
IN
)
Enable Input Threshold
Enable Input Current
V
EN
= 0V
V
EN
= 2.4V
3V
≤
V
IN
≤
40V, V
COMP
= 0.6V, I
SW
= 0
Shutdown, V
EN
= 0V
∆I
SW
= 1A, V
COMP
= 1.5V
0.4
–1
2.7
7
0.1
9
1.2
0
2
3.0
9
5
20
2.4
1
10
V
mA
µA
mA
V
µA
µA
Bold
type denotes specifications applicable to the full operating temperature range.
Note 1
Note 2
Devices are ESD sensitive. Handling precautions required.
For duty cycles (δ) between 50% and 95%, minimum guaranteed switch current is given by I
CL
= 0.833 (2-δ) for the MIC3172.
1997
4-17
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