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MIC2172/3172
100kHz 1.25A Switching Regulators
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
synchronization 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
designated 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 increased 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
•
•
•
•
•
•
•
•
•
•
•
•
•
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)
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)
•
•
•
•
___________________________________________________________________________________________________________
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 2006
M9999-041806
(408) 955-1690
Micrel
MIC2172/3172
Typical Applications
Figure 1. MIC2172 5V to 12V Boost Converter
Figure 2. MIC3172 Flyback Converter
Ordering Information
Part Number
Standard
MIC2172BN
MIC2172BM
MIC3172BN
MIC3172BM
Note:
1. Other Voltage available. Contact Micrel for details.
Pb-Free
MIC2172YN
MIC2172YM
MIC3172YN
MIC3172YM
Junction Temp. 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-pin SOIC
8-pin plastic DIP
8-pin SOIC
Pin Configuration
8-pin DIP (N)
8-pin SOIC (M)
April 2006
2
M9999-041806
(408) 955-1690
Micrel
MIC2172/3172
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 0.3
Ω
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 0.3
Ω
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
VIN
P GND 2
7
8
VSW
P GND 1
April 2006
3
M9999-041806
(408) 955-1690
Micrel
MIC2172/3172
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
Note 1, 3. Unless otherwise specified, V
IN
= 5V.
Parameter
Reference Section
Feedback Voltage (V
FB
)
Feedback Voltage Line
Regulation
Feedback Bias Current
(I
FB
)
Error Amplifier Section
Transconductance
(∆I
COMP
/∆V
FB
)
Voltage Gain
(∆V
COMP
/∆V
FB
)
Output Current
Output Swing
Compensation Pin
Threshold
ON Resistance
Current Limit
∆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
Output Switch Section
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
Ω
Ω
A
A
A
V
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
3V
≤
V
IN
≤
40V
310
Condition
Pin 2 tied to pin 3
1.220
1.214
1.240
1.264
1.274
0.03
750
1100
V
V
%/V
nA
nA
Min
Typ
Max
Units
Breakdown Voltage (BV)
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
4. Specification for packaged product only.
April 2006
4
M9999-041806
(408) 955-1690
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