Micrel MIC2172, MIC3172 User Manual

General Description

MIC2172/3172

100kHz 1.25A Switching Regulators

Features

The MIC2172 and MIC317 2 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 mak es it practical for step-do wn, inverting,
and Cuk configurations as well as isolated topologies.

Operating from 3V to 40V, the MIC2 172/3172 draws only
7mA of quiescent current making it attractive for battery
operated supplies.

The MIC3172 is for appl ications that require on/of f control
of the regulator. The MIC3172 is externally shutdown by
applying a TTL low s ignal to EN (enable) . When disable d,
the MIC3172 draws only leakage current (typically less
than 1µA). EN must be high for normal operation. For
applications not requ ir in g c ontrol , EN must be tied to V
TTL high.

The MIC2172 is for applications requiring two or more
SMPS regulators that op erate from the same input su pply.
The MIC2172 features a S YNC input which allows loc king
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 regu lat or s .

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 ava ilable in an 8-pin plastic DIP or
SOIC for –40°C to +85°C operation.

IN or

• 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 [phone] • fax + 1 [phone] • http://www.micrel.com

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Micrel MIC2172/3172

Typical Applications

Figure 1. MIC2172 5V to 12V Boost Converter

Ordering Information

Part Number

Standard Pb-Free

MIC2172BN MIC2172YN –40°C to +85°C 8-pin plastic DIP
MIC2172BM MIC2172YM –40°C to +85°C 8-pin SOIC
MIC3172BN MIC3172YN –40°C to +85°C 8-pin plastic DIP
MIC3172BM MIC3172YM –40°C to +85°C 8-pin SOIC

Note:

1. Other Voltage available. Contact Micrel for details.

Pin Configuration

Figure 2. MIC3172 Flyback Converter

Junction Temp. Range Package

8-pin DIP (N) 8-pin SOIC (M)

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Pin Description

Pin Number Pin Name Pin Function

1 S GND Signal Ground: Internal analog circuit ground. Connect directly to the input filter

capacitor for proper operation (see applications info). Keep separate from power
grounds.

2 COMP 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.

3 FB Feedback: Inverting input of error amplifier. Connect to external resistive divider

to set power supply output voltage.

4 (MIC2172) SYNC 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).

4 (MIC3172) EN Enable: Apply TTL high or connect to VIN to enable the regulator. Apply TTL low

or connect to ground to disable the regulator. Device draws only leakage current
(<1µA) when disabled.

5 VIN Supply Voltage: 3.0V to 40V
6 P GND 2

7 VSW Power Switch Collector: Collector of NPN switch. Connect to external inductor or

8 P GND 1

Power Ground #2: One of two NPN power switch emitters with 0.3
sense resistor in series. Required. Connect to external inductor or input voltage
ground depending on circuit topology.

input voltage depending on circuit topology.
Power Ground #1: One of two NPN power switch emitters with 0.3

sense resistor in series. Optional. For maximum power capability connect to P
GND 2. Floating pin reduces current limit by a factor of two.

Ω current

Ω current

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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
θ

8-pin PDIP................................................. 130°C/W

JA

8-pin SOIC................................................. 120°C/W

JA

Storage Temperature ................................–65°C to +150°C

Soldering (10 sec.) ...................................................+300°C

Electrical Characteristics MIC2172

Note 1, 3. Unless otherwise specified, V

Parameter Condition Min Typ Max Units
Reference Section

Feedback Voltage (VFB) 1.220

Feedback Voltage Line
Regulation

Feedback Bias Current

)

(I

FB

Error Amplifier Section

Transconductance

/∆VFB)

(∆I

COMP

Voltage Gain

COMP

/∆VFB)

(∆V
Output Current V

Output Swing High Clamp, VFB = 1V

Compensation Pin
Threshold

ON Resistance ISW = 1A, VFB = 0.8V 0.76 1

Current Limit Duty Cycle = 50%, TJ ≥ 25°C

Breakdown Voltage (BV) 3V ≤ VIN ≤ 40V

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.

Pin 2 tied to pin 3

3V ≤ VIN ≤ 40V

310 750

∆I

= ±25µA 3.0

COMP

0.9V ≤ V

= 1.5V 125

COMP

Low Clamp, V
Duty Cycle = 0 0.8

Duty Cycle = 50%, TJ < 25°C
Duty Cycle = 80%, Note 2

= 5mA

I

SW

IN = 5V.

1.240 1.264

1.214

1.274

0.03

1100

3.9 6.0

2.4

≤ 1.4V 500 800 2000 V/V

COMP

7.0

175 350

= 1.5V

FB

100

1.8

0.25

2.1

0.35

400

2.3

0.52

0.9 1.08

0.6

1.25

Output Switch Section

1.1

1.25

1.25
1

65

75 V

3

3.5

2.5

V
V

%/V

nA
nA

µA/mV
µA/mV

µA
µA

V
V

V
V

Ω
Ω

A
A
A

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Typical Characteristics MIC2172 (cont)

Parameter Condition Min Typ Max Units
Oscillator Section

Frequency (fO) 88

Duty Cycle [δ(max)]

100 112

85

80 89

115

95

kHz
kHz

%

Sync Coupling Capacitor
Required for Frequency

VPP = 3.0V

= 40V

V

PP

22

2.2

51

4.7

120

10

pF
pF

Lock

Input Supply Voltage Section

Minimum Operating

2.7

3.0

V

Voltage
Quiescent Current (IQ) 3V ≤ VIN ≤ 40V, V
Supply Current Increase

)

(∆I

IN

∆I

= 1A, V

SW

COMP

= 0.6V, ISW = 0 7

COMP

= 1.5V 9 20 mA

9

mA

Electrical Characteristics MIC3172

Note 1, 3. Unless otherwise specified, V

IN = 5V.

Parameter Condition Min Typ Max Units
Reference Section

Feedback Voltage (VFB) 1.224

Feedback Voltage Line

Pin 2 tied to pin 3

1.240 1.264

1.214

3V ≤ VIN ≤ 40V 0.07

1.274

%/V

V
V

Regulation
Feedback Bias Current

)

(I

FB

310 750

1100

nA
nA

Error Amplifier Section

Transconductance

/∆VFB)

(∆I

COMP

Voltage Gain

COMP

/∆VFB)

(∆V
Output Current V

Output Swing High Clamp, VFB = 1V

Compensation Pin
Threshold

∆I

= ±25µA 3.0

COMP

2.4

0.9V ≤ V

COMP

≤ 1.4V 500 800 2000 V/V

COMP

= 1.5V 125

100

1.8

Low Clamp, V

= 1.5V

FB

0.25

Duty Cycle = 0 0.8

0.6

3.9 6.0

7.0

175 350

400

2.1

0.35

2.3

0.52

0.9 1.08

1.25

µA/mV
µA/mV

µA
µA

V
V

V

V
Output Switch Section
ON Resistance ISW = 1A, VFB = 0.8V 0.76 1

1.1

Current Limit Duty Cycle = 50%, TJ ≥ 25°C

Duty Cycle = 50%, TJ < 25°C
Duty Cycle = 80%, Note 2

Breakdown Voltage (BV) 3V ≤ VIN ≤ 40V

= 5mA

I

SW

1.25

1.25
1

65

3.5

2.5

75 V

3

Ω
Ω

A
A
A

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Micrel MIC2172/3172

Typical Characteristics MIC3172 (cont)

Parameter Condition Min Typ Max Units
Oscillator Section

Frequency (fO) 88

Duty Cycle [δ(max)]

100 112

85

80 89

115

95

kHz
kHz

%

Sync Coupling Capacitor
Required for Frequency

VPP = 3.0V

= 40V

V

PP

22

2.2

51

4.7

120

10

pF
pF

Lock

Input Supply Voltage Section and Enable Section

Minimum Operating

2.7

3.0

V

Voltage
Quiescent Current (IQ) 3V ≤ VIN ≤ 40V, V
Supply Current Increase

)

(∆I

IN

∆I

= 1A, V

SW

COMP

= 0.6V, ISW = 0 7

COMP

= 1.5V 9 20 mA

Enable Input Threshold
Enable Input Current VEN = 0V

= 2.4V

V

EN

Bold type denotes specifications applicable to the full operating temperature range.
Note 1. Devices are ESD sensitive. Handling precautions required.

Note 2. For duty cycles (δ) between 50% and 95%, minimum guaranteed switch current is given by I
Note 3. Specification for packaged product only.

0.4

1.2

–1 0

2

= 0.833 (2- δ) for the MIC3172.

CL

9

2.4
1

10

mA

V

µA
µA

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