MIC38C43ABMTR - Micrel - Datasheet.Support

MIC38C42A/43A/44A/45A Micrel, Inc.

April 2005 1 M9999-042205

MIC38C42A/43A/44A/45A

BiCMOS Current-Mode PWM Controllers

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

Features

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

•–40°C to +85°C temperature range

meets UC284x specifications

•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

Oscillator

UVLO

Reference

VDD

VREF

RT/CT

2.5V

COMP

GND

ISNS

OUT

†

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

MIC38C42A/43A/44A/45A Micrel, Inc.

M9999-042205 2April 2005

Ordering Information

Part Number Temperature

Standard Pb-Free Range Package

MIC38C42ABM MIC38C42AYM –40°C to +85°C8-pin SOIC

MIC38C43ABM MIC38C43AYM –40°C to +85°C8-pin SOIC

MIC38C44ABM MIC38C44AYM –40°C to +85°C8-pin SOIC

MIC38C45ABM MIC38C45AYM –40°C to +85°C8-pin SOIC

MIC38C42ABMM MIC38C42AYMM –40°C to +85°C8-pin MM8™

MIC38C43ABMM MIC38C43AYMM –40°C to +85°C8-pin MM8™

MIC38C44ABMM MIC38C44AYMM –40°C to +85°C8-pin MM8™

MIC38C45ABMM MIC38C45AYMM –40°C to +85°C8-pin MM8™

UVLO Thresholds

Startup 8.4V Startup 14.5V

Duty Cycle Minimum Operating 7.6V Minimum Operating 9V

0% to 96% MIC38C43A MIC38C42A

0% to 50% MIC38C45A MIC38C44A

Selection Guide

Refer to the Part Number Cross Reference for a listings of Micrel devices equivalent to UC284x and UC384x devices.

MIC38C42A/43A/44A/45A Micrel, Inc.

April 2005 3 M9999-042205

Pin Description

Pin Number Pin Name Pin Function

1COMP Compensation: Connect external compensation network to modify the error

amplifier output.

2FBFeedback (Input): Error amplifier input. Feedback is 2.5V at desired output

voltage.

3ISNS Current Sense (Input): Current sense comparator input. Connect to current

sensing resistor or current transformer.

4RT/CT Timing Resistor/Timing Capacitor: Connect external RC network to select

switching frequency.

5GND Ground: Combined analog and power ground.

6OUT Power Output: Totem-pole output.

7VDD Analog Supply (Input): Controller circuitry supply input. Return to analog

ground (AGND).

8VREF 5V Reference (Output): Connect external RC network.

COMP

ISNS

RT/CT

VREF

VDD

OUT

GND

MIC38C4xA

8-Lead SOIC (M)

8-Lead MM8™ (MM)

Pin Configuration

MIC38C42A/43A/44A/45A Micrel, Inc.

M9999-042205 4April 2005

Electrical Characteristics(Note 6)

VDD = 15V, Note 4; RT = 11.0k; CT = 3.3nF; –40°C ≤ TA ≤ 85°C; unless noted

Parameter Test Conditions Min Typ Max Units

Reference Section

Output Voltage TA = 25°C, IO = 1mA 4.90 5.00 5.10 V

Line Regulation 12V ≤ VDD ≤ 18V, IO = 5µA220mV

Load Regulation 1 ≤ IO ≤ 20mA 1 25 mV

Temp. Stability Note 1 0.2 mV/°C

Total Output Variation Line, Load, Temp., Note 1 4.82 5.18 V

Output Noise Voltage 10Hz ≤ f ≤ 10kHz, TA = 25°C, Note 1 50 µV

Long Term Stability TA = 125°C, 1000 hrs., Note 1 525mV

Output Short Circuit –30 –80 –180 mA

Oscillator Section

Initial Accuracy TA = 25°C, Note 5 47 53 59 kHz

Voltage Stability 12 ≤ VDD ≤ 18V 0.2 1.0 %

Temp. Stability TMIN ≤ TA ≤ TMAX, Note 1 0.04 %/°C

Clock Ramp TA = 25°C, VRT/CT = 2V, Note 1 7.7 8.4 9.0 mA

Reset Current

Amplitude VRT/CT peak to peak 1.9 Vp-p

Error Amp Section

Input Voltage VCOMP = 2.5V 2.4 2.50 2.58 V

Input Bias Current VFB = 5.0V –0.1 –2 µA

AVOL 2 ≤ VO ≤ 4V 65 90 dB

Unity Gain Bandwidth Note 1 0.7 1.0 MHz

PSRR 12 ≤ VDD ≤ 18V 60 dB

Output Sink Current VFB = 2.7V, VCOMP = 1.1V 2 14 mA

Output Source Current VFB = 2.3V, VCOMP = 5V –0.3 –1 mA

VOUT High VFB = 2.3V, RL = 15k to ground 5 6.8 V

VOUT Low VFB = 2.7V, RL = 15k to VREF 0.1 1.1 V

Absolute Maximum Ratings

Supply Voltage (VDD) ....................................................20V

Switch Supply Voltage (VD) .......................................... 20V

Current Sense Voltage (VISNS) ..................... –0.3V to 5.5V

Feedback Voltage (VFB) ................................ –0.3V to 5.5V

Output Current (IOUT) ...................................................0.5A

Storage Temperature (TA) ....................... –65°C to +150°C

Operating Ratings

Junction Temperature (TJ) ........................................ 150°C

Package Thermal Resistance

8-Pin MM8™ (θJA) .............................................250°C/W

8-Pin SOIC (θJA) ...............................................170°C/W

MIC38C42A/43A/44A/45A Micrel, Inc.

April 2005 5 M9999-042205

Parameter Test Conditions Min Typ Max Units

Current Sense

Gain Notes 2, 3 2.85 3.0 3.15 V/V

MaximumThreshold VCOMP = 5V, Note 2 0.9 1 1.1 V

PSRR 12 ≤ VDD ≤ 18V, Note 2 70 dB

Input Bias Current –0.1 –2 µA

Delay to Output 120 250 ns

Output

RDS(ON) High ISOURCE = 200mA 20 Ω

RDS(ON) Low ISINK = 200mA 11 Ω

Rise Time TA = 25°C, CL = 1nF 40 80 ns

Fall Time TA = 25°C, CL = 1nF 30 60 ns

Undervoltage Lockout

Start Threshold MIC38C42A/4A 13.5 14.5 15.5 V

MIC38C43A/5A 7.8 8.4 9.0 V

Minimum Operating Voltage MIC38C42A/4A 8 9 10 V

MIC38C43A/5A 7.0 7.6 8.2 V

Pulse Width Modulator

Maximum Duty Cycle MIC38C42A/3A 94 96 %

MIC38C44A/5A 46 50 %

Minimum Duty Cycle 0%

Total Standby Current

Start-Up Current VDD = 13V for MIC38C42A/44A 100 230 µA

VDD = 7.5V for MIC38C43A/45A

Operating Supply Current VFB = VISNS = 0V 4.0 6.0 mA

Note 1: These parameters, although guaranteed, are not 100% tested in production.

Note 2: Parameter measured at trip point of latch with VEA = 0.

Note 3: Gain defined as:

A = V

V (I )

0 V (I ) 0.8V

PIN1

TH SNS

∆;≤≤

Note 4: Adjust VDD above the start threshold before setting at 15V.

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.

MIC38C42A/43A/44A/45A Micrel, Inc.

M9999-042205 6April 2005

Typical Characteristics

100

1x10

5x10

RESISTANCE (kΩ)

OSCILLATOR FREQUENCY (Hz)

Oscillator Frequency

Configuration

10nF

4.7nF

1nF

470pF

200pF

1.8nF

= 15V

100

1x1041x1051x106

OUTPUT DEAD TIME (%)

FREQUENCY (Hz)

MIC38C42/43 Output Dead Time

vs. Oscillator Frequency

= 15V

10nF

4.7nF

200pF

470pF

18nF

1nF

7.0

7.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

8.8

9.0

-60 -30 0 30 60 90 120 150

OSC. DISCHARGE CURRENT (mA)

TEMPERATURE (°C)

Oscillator Discharge

Current vs. Temperature

= 15V

OSC

= 2V

0.0

0.2

0.4

0.6

0.8

1.0

1.2

02468

CURRENT SENSE AMP THRESHOLD (V)

ERROR AMPLIFIER OUTPUT (V)

Current Sense Amplifier

vs. Error Amplifier Output

-50°C

25°C

125°C

100

120

-60 -30 0 30 60 90 120 150

VREF SHORT CURCUIT CURRENT (mA)

TEMPERATURE (°C)

Short-Circuit Reference

Current vs. Temperature

VDD = 15V

-15

-10

-5

0.0 0.2 0.4 0.6 0.8 1.0

OUTPUT VOLTAGE (V)

TIME (µs)

MIC38C4x

Output Waveform

VD = 15V

CL = 1nF

MIC38C42A/43A/44A/45A Micrel, Inc.

April 2005 7 M9999-042205

mended.

When designing high-frequency converters, avoid capacitive

and inductive coupling of the switching waveform into high-

impedance circuitry such as the error amplifier, oscillator, and

current sense amplifier. Avoid long printed-circuit traces and

component leads. Locate oscillator and compensation cir-

cuitry near the IC. Use high frequency decoupling capacitors

on VREF, and if necessary, on VDD. Return high di/dt currents

directly to their source and use large area ground planes.

Buck Converter

Refer to figure 1. When at least 26V is applied to the input,

C5 is charged through R2 until the voltage VDD is greater than

14.5V (the undervoltage lockout value of the MIC38C42).

Output switching begins when Q1 is turned on by the gate

drive transformer T1, charging the output filter capacitor C3

through L1. D5 supplies a regulated +12V to VDD once the

circuit is running.

Current sense transformer CT1 provides current feedback to

ISNS for current-mode operation and cycle-by-cycle current

limiting. This is more efficient than a high-power sense

resistor and provides the required ground-referenced level

shift.

When Q1 turns off, current flow continues from ground

through D1 and L1 until Q1 is turned on again.

The 100V Schottky diode D1 reduces the forward voltage

drop in the main current path, resulting in higher efficiency

than could be accomplished using an ultra-fast-recovery

diode. R1 and C2 suppress parasitic oscillations from D1.

Using a high-value inductance for L1 and a low-ESR capaci-

tor for C3 permits small capacitance with minimum output

ripple. This inductance value also improves circuit efficiency

by reducing the flux swing in L1.

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 cost and printed circuit

space.

Operating Current

Operating current has been reduced to 4mA compared to

11mA for a typical bipolar controller. The controller runs

cooler and the VDD hold-up capacitance required during

start-up may be reduced.

Output Driver

Complementary internal P- and N-channel MOSFETs pro-

duce rail-to-rail output voltages for better performance driving

external power MOSFETs. The driver transistor’s low on-

resistance and high peak current capability can drive gate

capacitances of greater than 1000pF. The value of output

capacitance which can be driven is determined only by the

rise/fall time requirements. Within the restrictions of output

capacity and controller power dissipation, maximum switch-

ing frequency can approach 500kHz.

Design Precautions

When operating near 20V, circuit transients can easily ex-

ceed the 20V absolute maximum rating, permanently damag-

ing the controller’s CMOS construction. To reduce tran-

sients, use a 0.1µF low-ESR capacitor to next to the controller’s

supply VDD (or VD for ‘-1’ versions) and ground connections.

Film type capacitors, such as Wima MKS2, are recom-

Figure 1. 500kHz, 25W, Buck Converter

VOUT

12V, 2A

COMP

ISNS

RT/CT GND

OUT

VDD

VREF

1000pF

1/2W 31DQ10

L1 48µH

3.3µFC4

0.1µF

6.19k

1.62k

200pF

16k 0.1µF

MBR030

0.1µF

6.8k

0.22µF

100k

IRF820

0.1µF

4.7µF

68k

M17Z105

1/4W

1N4001

1N765B

VIN

26V to 40V CT1

4.7Ω

MIC38C42A

0.1µF*

*Locate near MIC38C42 supply pins

MKS2

MIC38C42A/43A/44A/45A Micrel, Inc.

M9999-042205 8April 2005

Magnetic components are carefully chosen for minimal loss

at 500kHz. CT1 and T1 are wound on Magnetics, Inc. P-type

material toroids. L1 is wound on a Siemens N49 EFD core.

Symbol Custom Coil1ETS2

CT1 4923 ETS 92420

T1 4924 ETS 92419

L1 4925 ETS 92421

1. Custom Coils, Alcester, SD tel: (605) 934-2460

2. Energy Transformation Systems, Inc. tel: (415) 324-4949.

Test Conditions Results

Line Regulation VIN = 26V to 80V, IO = 2A 0.5%

Load Regulation VIN = 48V, IO = 0.2A to 2A 0.6%

Efficiency VIN = 48V, IO = 2A 90%

Output Ripple VIN = 48V, IO = 2A (20MHz BW) 100mV

Synchronous Buck Converter

Refer to figure 2. This MIC38C43 synchronous buck con-

verter uses an MIC5022 half-bridge driver to alternately drive

the PWM switch MOSFET (driven by GATEH, or high-side

output) and a MOSFET which functions as a synchronous

rectifier (driven by the GATEL, or low-side output).

The low-side MOSFET turns on when the high-side MOSFET

is off, allowing current to return from ground. Current flows

through the low-side MOSFET in the source to drain direc-

tion.

The on-state voltage drop of the low-side MOSFET is lower

than the forward voltage drop of an equivalent Schottky

rectifier. This lower voltage drop results in higher efficiency.

A sense resistor (5mΩ) is connected to the driver’s high-side

current sense inputs to provide overcurrent protection. Refer

to the MIC5020, MIC5021, and MIC5022 data sheets for

more information.

Figure 2. 100kHz, Synchronous Buck Converter

MIC38C43A

0.1µF

300k

4.3k

VOUT

5V, 8A

0.15µF

35µH

1000µF

Low ESR

0.1µFSMP60N06-14

VDD

VREF

GND

COMP

VOUT

RT/CT

ISNS

4.7nF

10k

6.8k

47k

3.3k

2200

470µF

25V

MIC5022

GATEH

SH+

GATEL

SH–

SL+

GND

FLT

VDD

+12V

5mΩ

0.1µF*

MKS2

*Locate near the MIC38C43 supply pins.

SL–

MIC38C42A/43A/44A/45A Micrel, Inc.

April 2005 9 M9999-042205

Package Information

45°

0°–8°

0.244 (6.20)

0.228 (5.79)

0.197 (5.0)

0.189 (4.8) SEATING

PLANE

0.026 (0.65)

MAX)

0.010 (0.25)



0.007 (0.18)

0.064 (1.63)

0.045 (1.14)

0.0098 (0.249)

0.0040 (0.102)

0.020 (0.51)

0.013 (0.33)

0.157 (3.99)

0.150 (3.81)

0.050 (1.27)

TYP

PIN 1

DIMENSIONS:

INCHES (MM)

0.050 (1.27)

0.016 (0.40)

8-Pin SOP (M)

0.008 (0.20)

0.004 (0.10)

0.039 (0.99)

0.035 (0.89)

0.021 (0.53)

0.012 (0.03) R

0.0256 (0.65) TYP

0.012 (0.30) R

5° MAX

0° MIN

0.122 (3.10)

0.112 (2.84)

0.120 (3.05)

0.116 (2.95)

0.012 (0.03)

0.007 (0.18)



0.005 (0.13)

0.043 (1.09)

0.038 (0.97)

0.036 (0.90)

0.032 (0.81)

DIMENSIONS:

INCH (MM)

0.199 (5.05)

0.187 (4.74)

8-Pin MSOP (MM)

MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com

This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.

Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.

Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can

reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into

the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s

use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify

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