MIC38C42/3/4/5 - Micrel Semiconductor, Inc.

MIC38C42/3/4/5 Micrel

August 2000 1 MIC38C42/3/4/5

MIC38C42/3/4/5

BiCMOS Current-Mode PWM Controllers

General Description

The MIC38C4x are fixed frequency, high performance, cur-

rent-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 effi-

ciency, 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 14-

pin devices separate the analog and power connections for

improved performance and power dissipation.

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 (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

Oscillator

UVLO

Reference

VDD

7 (12)

VREF

8 (14)

RT/CT

4 (7)

2 (3)

2.5V

COMP

1 (1)

GND*(AGND)

5 (9)

ISNS

3 (5)

(VD)

(11)

OUT

6 (10)

(PGND)

(8)

( ) 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

†

‡

35V

MM8 is a trademark of Micrel, Inc.

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

MIC38C42/3/4/5 Micrel

MIC38C42/3/4/5 2 August 2000

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

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

Selection Guide

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

MIC38C42/3/4/5 Micrel

August 2000 3 MIC38C42/3/4/5

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.

COMP

ISNS

RT/CT

VREF

VDD

OUT

GND

MIC38C4x

2NC NC13

3FB VDD12

4NC VD11

5ISNS OUT10

6NC AGND9

7RT/CT PGND8

1COMP VREF14

MIC38C4x-1

8-Pin DIP (N)

8-Lead SOIC (M)

8-Lead MM8™ (MM)

14-Pin DIP (-1BN)

14-Lead SOIC (-1BM)

Pin Configuration

MIC38C42/3/4/5 Micrel

MIC38C42/3/4/5 4 August 2000

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 TMIN ≤ TA ≤ TMAX, Note 1 0.04 %/°C

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

Reset Current TA = TMIN to TMAX 7.2 8.4 9.5 mA

Amplitude VRT/CT peak to peak 1.9 Vp-p

Error Amp Section

Input Voltage VCOMP = 2.5V 2.42 2.50 2.58 V

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

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 –0.5 –1mA

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

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

Operation at ≥18V may require

special precautions (Note 6).

Supply Voltage (VDD), Note 6 .......................................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, 38C42/3/4/5 (IOUT) .............................0.5A

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

Operating Ratings

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

Package Thermal Resistance

8-Pin Plastic DIP (θJA) .......................................125°C/W

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

MIC38C42/3/4/5 Micrel

August 2000 5 MIC38C42/3/4/5

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 –2µA

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 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 = VISNS = 0V 4.0 6.0 mA

Zener Voltage (VDD)I

DD = 25mA, Note 6 30 37 V

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 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.

MIC38C42/3/4/5 Micrel

MIC38C42/3/4/5 6 August 2000

Typical Characteristics

100

1x10

5x10

RESISTANCE (kΩ)

OSCILLATOR FREQUENCY (Hz)

Oscillator Frequency

Configuration

10nF

4.7nF

1nF

470pF

200pF

1.8nF

= 15V

100

1x10

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

REF

SHORT CURCUIT CURRENT (mA)

TEMPERATURE (°C)

Short-Circuit Reference

Current vs. Temperature

= 15V

-15

-10

-5

0.0 0.2 0.4 0.6 0.8 1.0

OUTPUT VOLTAGE (V)

TIME (µs)

MIC38C4x

Output Waveform

= 15V

= 1nF

MIC38C42/3/4/5 Micrel

August 2000 7 MIC38C42/3/4/5

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

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

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

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 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

Figure 1. 500kHz, 25W, Buck Converter

OUT

12V, 2A

COMP

ISNS

RT/CT GND

OUT

VDD

VREF

1000pF

1/2W 31DQ10

L1 48µH

3.3µF C4

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

26V to 40V CT1

4.7Ω

MIC38C42

0.1µF*

*Locate near MIC38C42 supply pins

MKS2

MIC38C42/3/4/5 Micrel

MIC38C42/3/4/5 8 August 2000

ripple. This inductance value also improves circuit efficiency

by reducing the flux swing in L1.

Magnetic components are carefully chosen for minimal loss

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

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

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

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

MIC38C43

0.1µF

300k

4.3k

VOUT

5V, 8A

0.15µF

35µH

1000µF

Low ESR

0.1µF SMP60N06-14

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–

MIC38C42/3/4/5 Micrel

August 2000 9 MIC38C42/3/4/5

Package Information

0.380 (9.65)

0.370 (9.40) 0.135 (3.43)

0.125 (3.18)

PIN 1

DIMENSIONS:

INCH (MM)

0.018 (0.57)

0.100 (2.54)

0.013 (0.330)

0.010 (0.254)

0.300 (7.62)

0.255 (6.48)

0.245 (6.22)

0.380 (9.65)

0.320 (8.13)

0.0375 (0.952)

0.130 (3.30)

8-Pin Plastic DIP (N)

.080 (1.524)

.015 (0.381)

.023 (.5842)

.015 (.3810)

.310 (7.874)

.280 (7.112)

.770 (19.558) MAX

.235 (5.969)

.215 (5.461)

.060 (1.524)

.045 (1.143)

.160 MAX

(4.064)

.160 (4.064)

.100 (2.540) .110 (2.794)

.090 (2.296) .400 (10.180)

.330 (8.362)

.015 (0.381)

.008 (0.2032)

.060 (1.524)

.045 (1.143)

PIN 1

14-Pin Plastic DIP (N)

MIC38C42/3/4/5 Micrel

MIC38C42/3/4/5 10 August 2000

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)

45°

3°–6°

0.244 (6.20)

0.228 (5.80)

0.344 (8.75)

0.337 (8.55)

0.006 (0.15)

SEATING

PLANE

0.026 (0.65)

MAX)0.016 (0.40)

TYP

0.154 (3.90)

0.057 (1.45)

0.049 (1.25)

0.193 (4.90)

0.050 (1.27)

TYP

PIN 1

DIMENSIONS:

INCHES (MM)

14-Pin SOP (M)

MIC38C42/3/4/5 Micrel

August 2000 11 MIC38C42/3/4/5

MIC38C42/3/4/5 Micrel

MIC38C42/3/4/5 12 August 2000

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.