MIC2171WU Micrel Inc, MIC2171WU Datasheet - Page 10

• Manufacturer Part Number: MIC2171WU
• Description: IC REG SW 100KHZ 2.5A TO263-5
• Manufacturer: Micrel Inc
• Type: Step-Down (Buck), Step-Up (Boost), Inverting, Cukr

Specifications of MIC2171WU

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Current - Output: 2.5A
• Frequency - Switching: 100kHz
• Voltage - Input: 3 ~ 40 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (5 leads + tab)
• Power - Output: 1.3W
• Number Of Pwm Outputs: 1
• On/off Pin: No
• Adjustable Output: No
• Switching Freq: 112KHz
• Operating Supply Voltage (max): 40V
• Output Current: 2.5A
• Output Voltage: 65V
• Synchronous Pin: No
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 5 +Tab
• Package Type: TO-263
• Duty Cycle: 95%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / RoHS Status: Compliant, Lead free / RoHS Compliant
• Other names: 576-1063

time, using the off-time to reset the transformer core. In
the application shown, the transformer core is reset by
the tertiary winding discharging T1’s peak magnetizing
current through D2.
For most forward converters the duty cycle is limited to
50%, allowing the transformer flux to reset with only two
times the input voltage appearing across the power
switch. Although during normal operation this circuit’s
duty cycle is well below 50%, the MIC2172 has a
maximum duty cycle capability of 90%. If 90% was
required during operation (start-up and high load
currents), a complete reset of the transformer during the
Micrel, Inc.
May 2007
12V
V
IN
C1
22µF
GND
MIC2171
Figure 6. MIC2171 Forward Converter
IN
1µF
C3
R 2
COMP
1k
S W
R1*
F B
* Voltage clipper
†
Q1
Duty cycle limiter
1N5819
†
1:1:1
C2*
D1*
T1
C4
D2
R 3
†
†
10
off-time would require the voltage across the power
switch to be ten times the input voltage. This would limit
the input voltage to 6V or less for forward converter
applications.
To prevent core saturation, the application given here
uses a duty cycle limiter consisting of Q1, C4 and R3.
Whenever the MIC2171 exceeds a duty cycle of 50%,
T1’s reset winding current turns Q1 on. This action
reduces the duty cycle of the MIC2171 until T1 is able to
reset during each cycle.
1N5819
D3
1N5819
L1 100µH
D4
470µF
C5
R 5
1.24k
1%
R 4
3.74k
1%
V
5V, 1A
OU T
M9999-051107
MIC2171