Datasheet MIC38C43-1BM, MIC38C43-1BN, MIC38C43BM, MIC38C43BMM, MIC38C42BN Datasheet (MICREL)

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MIC38C42/3/4/5 Micrel

MIC38C42/3/4/5

BiCMOS Current-Mode PWM Controllers

General Description

The MIC38C4x 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 4.0 mA typical. Decreased output rise and fall times drive larger MOSFETs, and rail-to-rail output capability increases efficiency, especially at lower supply voltages. The MIC38C4x also features a trimmed oscillator discharge current and bandgap reference.

MIC38C4x denotes 8-pin plastic DIP, SOIC, and MM8™ packages. MIC38C4x-1 denotes 14-pin plastic DIP and SOIC packages. 8-pin devices feature small size, while 14pin devices separate the analog and power connections for improved performance and power dissipation.

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 (50µA 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(A)

• 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

For fast rise and fall times and higher output drive, refer to the MIC38HC4x.

Functional Diagram

VDD

7 (12)

VREF

8 (14)

RT/CT

4 (7)

2 (3)

2.5V

( ) pins are on MIC38C4x-1 (14-lead) versions only * MIC38C4x (8-lead) versions only

†

MIC38C42, MIC38C43 (96% max. duty cycle) versions only

‡

MIC38C44, MIC38C45 (50% max. duty cycle) versions only

MM8 is a trademark of Micrel, Inc.

35V

COMP

1 (1)

Reference

Oscillator

GND*(AGND)

5 (9)

ISNS

3 (5)

UVLO

(VD)

†

‡

(11)

OUT

6 (10)

(PGND)

(8)

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com

August 2000 1 MIC38C42/3/4/5

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MIC38C42/3/4/5 Micrel

Ordering Information

Part Number Temperature Range Package

MIC38C42BN –40°C to +85°C 8-pin Plastic DIP

MIC38C43BN –40°C to +85°C 8-pin Plastic DIP

MIC38C44BN –40°C to +85°C 8-pin Plastic DIP

MIC38C45BN –40°C to +85°C 8-pin Plastic DIP

MIC38C42-1BN –40°C to +85°C 14-pin Plastic DIP

MIC38C43-1BN –40°C to +85°C 14-pin Plastic DIP

MIC38C44-1BN –40°C to +85°C 14-pin Plastic DIP

MIC38C45-1BN –40°C to +85°C 14-pin Plastic DIP

MIC38C42BM –40°C to +85°C 8-pin SOIC

MIC38C43BM –40°C to +85°C 8-pin SOIC

MIC38C44BM –40°C to +85°C 8-pin SOIC

MIC38C45BM –40°C to +85°C 8-pin SOIC

MIC38C42BMM –40°C to +85°C 8-pin MM8™

MIC38C43BMM –40°C to +85°C 8-pin MM8™

MIC38C44BMM –40°C to +85°C 8-pin MM8™

MIC38C45BMM –40°C to +85°C 8-pin MM8™

MIC38C42-1BM –40°C to +85°C 14-pin SOIC

MIC38C43-1BM –40°C to +85°C 14-pin SOIC

MIC38C44-1BM –40°C to +85°C 14-pin SOIC

MIC38C45-1BM –40°C to +85°C 14-pin SOIC

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

Selection Guide

UVLO Thresholds

Startup 8.4V Startup 14.5V

Duty Cycle Minimum Operating 7.6V Minimum Operating 9V

0% to 96% MIC38C43 MIC38C42

0% to 50% MIC38C45 MIC38C44

MIC38C42/3/4/5 2 August 2000

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2NC NC13

3FB VDD12

4NC VD11

5ISNS OUT10

6NC AGND9

7RT/CT PGND8

1COMP VREF14

MIC38C4x-1

Pin Configuration

MIC38C4x

COMP

ISNS

RT/CT

VREF

VDD

OUT

GND

8-Pin DIP (N)

8-Lead SOIC (M)

14-Pin DIP (-1BN)

14-Lead SOIC (-1BM)

8-Lead MM8™ (MM)

Pin Description

Pin Number Pin Number Pin Name Pin Function

N, M, MM -1BN, -1BM

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

amplifier output.

2 NC Not internally connected.

2 3 FB Feedback (Input): Error amplifier input. Feedback is 2.5V at desired output

voltage.

4 NC Not internally connected.

3 5 ISNS Current Sense (Input): Current sense comparator input. Connect to current

sensing resistor or current transformer.

6 NC Not internally connected.

4 7 RT/CT Timing Resistor/Timing Capacitor: Connect external RC network to select

switching frequency.

5 GND Ground: Combined analog and power ground.

8 PGND Power Ground: N-channel driver transistor ground.

9 AGND Analog Ground: Controller circuitry ground.

6 10 OUT Power Output: Totem-pole output.

11 VD Power Supply (Input): P-channel driver transistor supply input. Return to

power ground (PGND).

7 12 VDD Analog Supply (Input): Controller circuitry supply input. Return to analog

ground (AGND).

13 NC Not internally connected.

8 14 VREF 5V Reference (Output): Connect external RC network.

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Absolute Maximum Ratings

Zener Current (VDD) ...................................................30mA

Operation at

special precautions (Note 6).

Supply Voltage (V

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

Current Sense Voltage (V Feedback Voltage (V Output Current, 38C42/3/4/5 (I Storage Temperature (T

≥18V may require

), Note 6 .......................................20V

) ..................... –0.3V to 5.5V

ISNS

) ................................ –0.3V to 5.5V

) ............................. 0.5A

OUT

) ....................... –65°C to +150°C

Operating Ratings

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

Package Thermal Resistance

8-Pin Plastic DIP (θ

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

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

14-Pin Plastic DIP (θJA) ....................................... 90°C/W

14-Pin SOIC (θJA) .............................................145°C/W

) ....................................... 125°C/W

Electrical Characteristics

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 = 5µA, Note 6 220mV

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 49 52 55 kHz

Voltage Stability 12 ≤ VDD ≤ 18V, Note 6 0.2 1.0 %

Temp. Stability T

Clock Ramp TA = 25°C, V

Reset Current TA = T

Amplitude V

Error Amp Section

Input Voltage V

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

VOL

Unity Gain Bandwidth Note 1 0.7 1.0 MHz

≤ TA ≤ T

MIN

to T

MIN

peak to peak 1.9 Vp-p

RT/CT

= 2.5V 2.42 2.50 2.58 V

COMP

2 ≤ VO ≤ 4V 65 90 dB

, Note 1 0.04 %/°C

MAX

= 2V 7.7 8.4 9.0 mA

RT/CT

MAX

7.2 8.4 9.5 mA

PSRR 12 ≤ VDD ≤ 18V 60 dB

Output Sink Current VFB = 2.7V, V

Output Source Current VFB = 2.3V, V

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

OUT

Low VFB = 2.7V, RL = 15k to V

OUT

= 1.1V 2 14 mA

COMP

= 5V –0.5 –1mA

COMP

REF

0.1 1.1 V

MIC38C42/3/4/5 4 August 2000

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Parameter Test Conditions Min Typ Max Units

Current Sense

Gain Notes 2, 3 2.85 3.0 3.15 V/V

MaximumThreshold V

= 5V, Note 2 0.9 1 1.1 V

COMP

PSRR 12 ≤ VDD ≤ 18V, Note 2 70 dB

Input Bias Current –0.1 –2 µA

Delay to Output 120 250 ns

Output

High I

DS(ON)

Low I

DS(ON)

SOURCE

SINK

= 200mA 20 Ω

= 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 MIC38C42/4 13.5 14.5 15.5 V

MIC38C43/5 7.8 8.4 9.0 V

Minimum Operating Voltage MIC38C42/4 8 9 10 V

MIC38C43/5 7.0 7.6 8.2 V

Pulse Width Modulator

Maximum Duty Cycle MIC38C42/3 94 96 %

MIC38C44/5 46 50 %

Minimum Duty Cycle 0%

Total Standby Current

Start-Up Current VDD = 13V for MIC38C42/44 50 200 µA

VDD = 7.5V for MIC38C43/45

Operating Supply Current VFB = V

Zener Voltage (VDD)I

= 25mA, Note 6 30 37 V

= 0V 4.0 6.0 mA

ISNS

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:

∆

PIN1

A =

V (I )

; ≤≤

0 V (I ) 0.8V

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 MIC38C44, and

MIC38C45 equals one half the oscillator frequency.

Note 6: On 8-pin version, 20V is maximum input on pin 7, as this is also the supply pin for the output stage. On 14-pin version, 40V is

maximum for pin 12 and 20V maximum for pin 11.

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MIC38C42/3/4/5 Micrel

Typical Characteristics

Oscillator Frequency

100

RESISTANCE (kΩ) R

1x10

Configuration

200pF

470pF

1.8nF

4.7nF 10nF

VDD = 15V

OSCILLATOR FREQUENCY (Hz)

1x10

1nF

5x10

Current Sense Amplifier

vs. Error Amplifier Output

1.2

1.0

0.8

0.6

0.4

0.2

0.0

CURRENT SENSE AMP THRESHOLD (V)

125°C

25°C

-50°C

02468

ERROR AMPLIFIER OUTPUT (V)

MIC38C42/43 Output Dead Time

vs. Oscillator Frequency

100

VDD = 15V

4.7nF

10nF

OUTPUT DEAD TIME (%)

1x10

FREQUENCY (Hz)

1x10

18nF

1nF

200pF

470pF

1x10

Short-Circuit Reference

Current vs. Temperature

120

100

VDD = 15V

SHORT CURCUIT CURRENT (mA)

REF

-60 -30 0 30 60 90 120 150

TEMPERATURE (°C)

Oscillator Discharge

Current vs. Temperature

9.0

8.8

8.6

8.4

8.2

8.0

7.8

7.6

7.4

7.2

7.0

OSC. DISCHARGE CURRENT (mA)

-60 -30 0 30 60 90 120 150 TEMPERATURE (°C)

VDD = 15V V

= 2V

OSC

MIC38C4x

Output Waveform

-5 VD = 15V

OUTPUT VOLTAGE (V)

-10

= 1nF

-15

0.0 0.2 0.4 0.6 0.8 1.0 TIME (µs)

MIC38C42/3/4/5 6 August 2000

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MIC38C42/3/4/5 Micrel

Application Information

Familiarity with 384x converter designs is assumed.

The MIC38C4x has been designed to be compatible with 384xA series controllers.

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 produce rail-to-rail output voltages for better performance driving external power MOSFETs. The driver transistor’s low onresistance 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 switching frequency can approach 500kHz.

Design Precautions

When operating near 20V, circuit transients can easily exceed the 20V absolute maximum rating, permanently damaging the controller’s CMOS construction. To reduce transients, use a 0.1µF low-ESR capacitor to next to the controller’s

supply V

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

Film type capacitors, such as Wima MKS2, are recommended.

When designing high-frequency converters, avoid capacitive and inductive coupling of the switching waveform into highimpedance circuitry such as the error amplifier, oscillator, and current sense amplifier. Avoid long printed-circuit traces and component leads. Locate oscillator and compensation circuitry near the IC. Use high frequency decoupling capacitors on V

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

REF

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 capacitor for C3 permits small capacitance with minimum output

26V to 40V

M17Z105

1/4W

R2 68k

MBR030

6.8k

0.22µF

R4 18

100k

CT1

0.1µF*

MIC38C42

COMP

ISNS

RT/CT GND

C7 200pF

MKS2

VREF

VDD

OUT

16k

0.1µF

4.7µF

0.1µF

1N765B

4.7Ω

0.1µF

IRF820

L1 48µH

31DQ10

R1 10 1/2W

1000pF

*Locate near MIC38C42 supply pins

3.3µFC40.1µF

1N4001

6.19k 1%

1.62k 1%

OUT

12V, 2A

Figure 1. 500kHz, 25W, Buck Converter

August 2000 7 MIC38C42/3/4/5

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MIC38C42/3/4/5 Micrel

ripple. This inductance value also improves circuit efficiency by reducing the flux swing in L1.

Magnetic components are carefully chosen for minimal loss

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 converter 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 direction.

+12V

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 Coil

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.

ETS

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.

6.8k

2200

10k

47k

3.3k

300k

10k

4.3k

0.15µF

4.7nF

MIC5022

VDD

0.1µF

MIC38C43

VREF

COMP

ISNS

RT/CT

VDD

VOUT

GND

*Locate near the MIC38C43 supply pins.

470µF

0.1µF* MKS2

25V

FLT

GND

GATEH

GATEL

SH+

SH–

SL+

SL–

Figure 2. 100kHz, Synchronous Buck Converter

0.1µF

SMP60N06-14

5mΩ

35µH

OUT

5V, 8A

1000µF Low ESR

MIC38C42/3/4/5 8 August 2000

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MIC38C42/3/4/5 Micrel

Package Information

PIN 1

DIMENSIONS:

INCH (MM)

.235 (5.969) .215 (5.461)

.160 MAX

(4.064)

0.018 (0.57)

0.100 (2.54)

0.380 (9.65)

0.370 (9.40)

8-Pin Plastic DIP (N)

.770 (19.558) MAX

.060 (1.524) .045 (1.143)

0.135 (3.43)

0.125 (3.18)

0.130 (3.30)

0.0375 (0.952)

0.255 (6.48)

0.245 (6.22)

0.300 (7.62)

0.013 (0.330)

0.010 (0.254)

0.380 (9.65)

0.320 (8.13)

PIN 1

.310 (7.874) .280 (7.112)

.080 (1.524) .015 (0.381)

.160 (4.064) .100 (2.540)

.110 (2.794) .090 (2.296)

.060 (1.524) .045 (1.143)

.023 (.5842) .015 (.3810)

14-Pin Plastic DIP (N)

.015 (0.381)

.008 (0.2032)

.400 (10.180)

.330 (8.362)

August 2000 9 MIC38C42/3/4/5

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MIC38C42/3/4/5 Micrel

0.026 (0.65) MAX)

PIN 1

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)

0.050 (1.27) TYP

0.197 (5.0)

0.189 (4.8)

8-Pin SOP (M)

0.199 (5.05)

0.187 (4.74)

0.120 (3.05)

0.116 (2.95)

0.020 (0.51)

0.013 (0.33)

0.0098 (0.249)

0.0040 (0.102)

0°–8°

SEATING

PLANE

0.043 (1.09)

0.038 (0.97)

0.012 (0.30) R

DIMENSIONS: INCHES (MM)

0.050 (1.27)

0.016 (0.40)

0.244 (6.20)

0.228 (5.79)

45°

0.010 (0.25)

0.007 (0.18)

DIMENSIONS:

INCH (MM)

0.007 (0.18)

0.005 (0.13)

0.012 (0.03)

0.0256 (0.65) TYP

0.154 (3.90)

0.026 (0.65) MAX)

0.057 (1.45)

0.049 (1.25)

0.050 (1.27) TYP

0.344 (8.75)

0.337 (8.55)

0.008 (0.20)

0.004 (0.10)

8-Pin MSOP (MM)

PIN 1

0.016 (0.40) TYP

0.006 (0.15)

SEATING

PLANE

14-Pin SOP (M)

5° MAX

0° MIN

DIMENSIONS:

INCHES (MM)

0.012 (0.03) R

0.039 (0.99)

0.035 (0.89)

0.021 (0.53)

0.193 (4.90)

45°

3°–6°

0.244 (6.20)

0.228 (5.80)

MIC38C42/3/4/5 10 August 2000

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MIC38C42/3/4/5 Micrel

August 2000 11 MIC38C42/3/4/5

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MIC38C42/3/4/5 Micrel

MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com

This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or

other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.

MIC38C42/3/4/5 12 August 2000