mic38c44a Micrel Semiconductor, mic38c44a Datasheet

mic38c44a

Manufacturer Part Number

mic38c44a

Description

Mic38c42a/mic38c43a/mic38c44a/mic38c45a Bicmos Current-mode Pwm Controllers

Manufacturer

Micrel Semiconductor

Datasheet

1.MIC38C44A.pdf (9 pages)

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MIC38C42A/43A/44A/45A

General Description

The MIC38C4xA are fixed frequency, high performance,

current-mode PWM controllers. Micrel’s BiCMOS devices

are pin compatible with 384x bipolar devices but feature

several improvements.

Undervoltage lockout circuitry allows the ’42 and ’44 versions

to start up at 14.5V and operate down to 9V, and the ’43 and

’45 versions start at 8.4V with operation down to 7.6V. All

versions operate up to 20V.

When compared to bipolar 384x devices operating from a

15V supply, start-up current has been reduced to 50µA

typical and operating current has been reduced to 4.0mA

typical. Decreased output rise and fall times drive larger

MOSFETs, and rail-to-rail output capability increases effi-

ciency, especially at lower supply voltages. The MIC38C4xA

also features a trimmed oscillator discharge current and

bandgap reference.

The MIC38C4xA family is available in 8-pin SOIC and MSOP-

8 (MM8) package options

For fast rise and fall times and higher output drive, refer to the

MIC38HC4x.

Functional Diagram

MM8 is a trademark of Micrel, Inc.

April 2005

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

RT/CT

VREF

VDD

†

‡

MIC38C42A, MIC38C43A (96% max. duty cycle) versions only

MIC38C44A, MIC38C45A (50% max. duty cycle) versions only

2.5V

COMP

Reference

Oscillator

GND

ISNS

Features

• Fast 40ns output rise and 30ns output fall times

• –40°C to +85°C temperature range

• High-performance, low-power BiCMOS Process

• Ultralow start-up current (100µA typical)

• Low operating current (4mA typical)

• CMOS outputs with rail-to-rail swing

• ≥ 500kHz current-mode operation

• Trimmed 5V bandgap reference

• Pin-for-pin compatible with UC3842/3843/3844/3845

• Trimmed oscillator discharge current

• UVLO with hysteresis

• Low cross-conduction currents

Applications

• Current-mode, off-line, switched-mode power supplies

• Current-mode, dc-to-dc converters.

• Step-down “buck” regulators

• Step-up “boost” regulators

• Flyback, isolated regulators

• Forward converters

• Synchronous FET converters

UVLO

meets UC284x specifications

BiCMOS Current-Mode PWM Controllers

MIC38C42A/43A/44A/45A

†

‡

OUT

M9999-042205

Micrel, Inc.

Related parts for mic38c44a

mic38c44a Summary of contents

Page 1

... MIC38C42A, MIC38C43A (96% max. duty cycle) versions only † ‡ MIC38C44A, MIC38C45A (50% max. duty cycle) versions only MM8 is a trademark of Micrel, Inc. Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com ...

Page 2

... MIC38C45AYMM –40°C to +85°C UVLO Thresholds Startup 8.4V Startup 14.5V Minimum Operating 7.6V Minimum Operating 9V MIC38C43A MIC38C42A MIC38C45A MIC38C44A 2 Micrel, Inc. Package 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin MM8™ 8-pin MM8™ 8-pin MM8™ ...

Page 3

MIC38C42A/43A/44A/45A Pin Configuration Pin Description Pin Number Pin Name 1 COMP ISNS 4 RT/CT 5 GND 6 OUT 7 VDD 8 VREF April 2005 MIC38C4xA COMP 1 8 VREF VDD ISNS 3 6 OUT ...

Page 4

MIC38C42A/43A/44A/45A Absolute Maximum Ratings Supply Voltage (V ) .................................................... 20V DD Switch Supply Voltage (V ) .......................................... 20V D Current Sense Voltage (V ) ..................... –0.3V to 5.5V ISNS Feedback Voltage (V ) ................................ –0.3V to 5.5V FB Output Current ...

Page 5

... Note 4: Adjust V above the start threshold before setting at 15V. DD Note 5: Output frequency equals oscillator frequency for the MIC38C42 and MIC38C43. Output frequency for the MIC38C44A, and MIC38C45A equals one half the oscillator frequency. Note 6: Specification for packaged product only. April 2005 = 5V, Note 2 ≤ ...

Page 6

MIC38C42A/43A/44A/45A Typical Characteristics Oscillator Frequency Configuration 100 200pF 470pF 1nF 10 1.8nF 4.7nF 10nF V = 15V 1x10 1x10 5x10 OSCILLATOR FREQUENCY (Hz) Current Sense Amplifier vs. Error Amplifier Output 1.2 1.0 125°C 0.8 0.6 ...

Page 7

MIC38C42A/43A/44A/45A Application Information Familiarity with 384x converter designs is assumed. MIC38C4x Advantages Start-up Current Start-up current has been reduced to an ultra-low 50µA (typical) permitting higher-valued, lower-wattage, start-up resistors (powers controller during power supply start-up). The reduced resistor wattage reduces ...

Page 8

MIC38C42A/43A/44A/45A Magnetic components are carefully chosen for minimal loss at 500kHz. CT1 and T1 are wound on Magnetics, Inc. P-type material toroids wound on a Siemens N49 EFD core. Test Conditions Line Regulation V = 26V to 80V, ...

Page 9

MIC38C42A/43A/44A/45A Package Information 0.026 (0.65) 0.157 (3.99) 0.150 (3.81) 0.064 (1.63) 0.045 (1.14) 0.122 (3.10) 0.112 (2.84) 0.036 (0.90) 0.032 (0.81) 0.012 (0.03) 0.0256 (0.65) TYP MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA + 1 (408) 944-0800 ...

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