PDF《MIC4575》

5 SHDN Shutdown (Input): Logic low enables regulator. Logic high (>

2.4V) shuts down regulator. Pin Configuration TAB

5 SHDN

4 FB

3 GND

2 SW

1 VIN 5-Lead TO-220 (T) TAB

5 SHDN

4 FB

3 GND

2 SW

1 VIN 5-Lead TO-263 (U) June

2005 3 M9999-062105 MIC4575 Micrel, Inc. Electrical Characteristics VIN = 12V;

ILOAD = 200mA;

TJ = 25°C, bold values indicate C40°C ≤ TJ ≤ +85°C;

unless noted. Parameter Condition Min Typ Max Units MIC4575 [Adjustable] Feedback Voltage 1.217 1.230 1.243 V Feedback Voltage 8V ≤ VIN ≤ 24V, 0.2A ≤ ILOAD ≤ 1A 1.193 1.230 1.267 V 1.180 1.280 V Efficiency ILOAD = 1A, VOUT = 5V

77 % Feedback Bias Current

50 100 nA

500 nA MIC4575-3.3 Output Voltage 3.234 3.3 3.366 V Output Voltage 6V ≤ VIN ≤ 24V, 0.2A ≤ ILOAD ≤ 1A 3.168 3.3 3.432 V 3.135 3.465 V Efficiency ILOAD = 1A

72 % MIC4575-5.0 Output Voltage 4.900 5.0 5.100 V Output Voltage 8V ≤ VIN ≤ 24V, 0.2A ≤ ILOAD ≤ 1A 4.800 5.0 5.200 V 4.750 5.250 V Efficiency ILOAD = 1A

77 % MIC4575 / -3.3 / -5.0 Oscillator Frequency

180 200

220 kHz Saturation Voltage IOUT = 1A

1 1.3 V 1.5 V Maximum Duty Cycle (On) FB connected to 0V

90 95 % Current Limit Peak Current, tON ≤ 3?s 1.7 2.2 3.0 A 1.3 3.2 A Output Leakage Current VIN = 24V, FB connected to 0V Output = 0V

0 2 mA Output = C1V 7.5

35 mA Quiescent Current

5 10 mA Standby Quiescent Current SHDN = 5V (regulator off)

50 200 ?A SHDN Input Logic Level VOUT = 0V (regulator off) 2.2 1.4 V 2.4 V VOUT = 3.3 or 5V (regulator on) 1.2 1.0 V 0.8 V SHDN Input Current SHDN = 5V (regulator off)

4 30 ?A SHDN = 0V (regulator on) C10 0.01

10 ?A General Note: Devices are ESD protected, however, handling precautions are recommended. Note 1: The MIC4575 is not guaranteed to survive a short circuit to ground for input voltage above 24V. Absolute Maximum Ratings Supply Voltage (VIN) Note

1 40V Shutdown Voltage (VSHDN)0.3V to +36V Output Switch (VSW) steady state 1V Storage Temperature (TS)65°C to 150°C Operating Ratings Supply Voltage (VIN)24V Junction Temperature 150°C Package Thermal Resistance TO-220, TO-263 (θJA)65°C/W TO-220, TO-263 (θJC)2°C/W MIC4575 Micrel, Inc. M9999-062105

4 June

2005 200kHz Oscillator 1.23V Bandgap 1A Switch Thermal Shutdown Current Limit Driver Internal Regulator FB SW GND VIN +24V max. CIN COUT L1 D1 Shutdown Enable SHDN VOUT MIC4575 [Adjustable] R1 R2 Com- parator Error Amp. VOUT VREF R1 R2 +

1 R1 R2 VOUT VREF

1 200kHz Oscillator 1.23V Bandgap 1A Switch Thermal Shutdown Current Limit Driver Internal Regulator FB SW GND VIN +24V max. CIN COUT L1 D1 Shutdown Enable SHDN VOUT MIC4575-x.x R1 R2 Com- parator Error Amp. Block Diagram with External Components Adjustable Step-Down Regulator Block Diagram with External Components Fixed Step-Down Regulator Block Diagrams June

2005 5 M9999-062105 MIC4575 Micrel, Inc. Functional Description The MIC4575 is a variable duty cycle switch-mode regulator with an internal power switch. Refer to the block diagrams. Supply Voltage The MIC4575 operates from a +4V to +24V unregulated input. Highest efficiency operation is from a supply voltage around +15V. Enable/Shutdown The shutdown (SHDN) input is TTL compatible. Ground the input if unused. A logic-low enables the regulator. A logic- high shuts down the internal regulator which reduces the current to typically 50?A. Feedback Fixed versions of the regulator have an internal resistive divider from the feedback (FB) pin. Connect FB directly to the output line. Adjustable versions require an external resistive voltage divider from the output voltage to ground, connected from the 1.23V tap to FB. Duty Cycle Control A fixed-gain error amplifier compares the feedback signal with a 1.23V bandgap voltage reference. The resulting error amplifier output voltage is compared to a 200kHz sawtooth waveform to produce a voltage controlled variable duty cycle output. A higher feedback voltage increases the error amplifier output voltage. A higher error amplifier voltage (comparator inverting input) causes the comparator to detect only the peaks of the sawtooth, reducing the duty cycle of the com- parator output. A lower feedback voltage increases the duty cycle. Output Switching When the internal switch is on, an increasing current flows from the supply VIN, through external storage inductor L1, to output capacitor COUT and the load. Energy is stored in the inductor as the current increases with time. When the internal switch is turned off, the collapse of the magnetic field in L1 forces current to flow through fast recovery diode D1, charging COUT. Output Capacitor External output capacitor COUT provides stabilization and reduces ripple. Return Paths During the on portion of the cycle, the output capacitor and load currents return to the supply ground. During the off portion of the cycle, current is being supplied to the output capacitor and load by storage inductor L1, which means that D1 is part of the high-current return path. Applications Information The applications circuits that follow have been constructed and tested. Refer to Application Note