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MIC38C42A/43A/44A/45A
Micrel, Inc.
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 50A 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 efficiency, 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 MSOP8 (MM8) package options For fast rise and fall times and higher output drive, refer to the MIC38HC4x.
Features
* Fast 40ns output rise and 30ns output fall times * -40C to +85C temperature range meets UC284x specifications * High-performance, low-power BiCMOS Process * Ultralow start-up current (100A 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
Functional Diagram
VDD
7
VREF
8
5V Reference
UVLO
RT/CT
4
Oscillator T Q
OUT
6
FB
2
2R 2.5V R S R Q
COMP
1
GND
5
ISNS
3
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
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MIC38C42A/43A/44A/45A
Micrel, Inc.
Ordering Information
Standard Part Number Pb-Free MIC38C42AYM MIC38C43AYM MIC38C44AYM MIC38C45AYM MIC38C42AYMM MIC38C43AYMM MIC38C44AYMM MIC38C45AYMM Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C Package 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin MM8TM 8-pin MM8TM 8-pin MM8TM 8-pin MM8TM
MIC38C42ABM MIC38C43ABM MIC38C44ABM MIC38C45ABM MIC38C42ABMM MIC38C43ABMM MIC38C44ABMM MIC38C45ABMM
Refer to the Part Number Cross Reference for a listings of Micrel devices equivalent to UC284x and UC384x devices.
Selection Guide
UVLO Thresholds Duty Cycle 0% to 96% 0% to 50% Startup 8.4V Minimum Operating 7.6V MIC38C43A MIC38C45A Startup 14.5V Minimum Operating 9V MIC38C42A MIC38C44A
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Micrel, Inc.
Pin Configuration
MIC38C4xA
COMP 1 FB 2 ISNS 3 RT/CT 4
8 7 6 5
VREF VDD OUT GND
8-Lead SOIC (M) 8-Lead MM8TM (MM)
Pin Description
Pin Number 1 2 3 4 5 6 7 8 Pin Name COMP FB ISNS RT/CT GND OUT VDD VREF Pin Function Compensation: Connect external compensation network to modify the error amplifier output. Feedback (Input): Error amplifier input. Feedback is 2.5V at desired output voltage. Current Sense (Input): Current sense comparator input. Connect to current sensing resistor or current transformer. Timing Resistor/Timing Capacitor: Connect external RC network to select switching frequency. Ground: Combined analog and power ground. Power Output: Totem-pole output. Analog Supply (Input): Controller circuitry supply input. Return to analog ground (AGND). 5V Reference (Output): Connect external RC network.
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MIC38C42A/43A/44A/45A
Micrel, Inc.
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) ....................... -65C to +150C
Operating Ratings
Junction Temperature (TJ) ........................................ 150C Package Thermal Resistance 8-Pin MM8TM (JA) ............................................. 250C/W 8-Pin SOIC (JA) ............................................... 170C/W
Electrical Characteristics(Note 6)
VDD = 15V, Note 4; RT = 11.0k; CT = 3.3nF; -40C TA 85C; unless noted Parameter Reference Section Output Voltage Line Regulation Load Regulation Temp. Stability Total Output Variation Output Noise Voltage Long Term Stability Output Short Circuit Oscillator Section Initial Accuracy Voltage Stability Temp. Stability Clock Ramp Reset Current Amplitude Error Amp Section Input Voltage Input Bias Current AVOL Unity Gain Bandwidth PSRR Output Sink Current Output Source Current VOUT High VOUT Low VCOMP = 2.5V VFB = 5.0V 2 VO 4V Note 1 12 VDD 18V VFB = 2.7V, VCOMP = 1.1V VFB = 2.3V, VCOMP = 5V VFB = 2.3V, RL = 15k to ground VFB = 2.7V, RL = 15k to VREF 65 0.7 60 2 -0.3 5 14 -1 6.8 0.1 1.1 2.4 2.50 -0.1 90 1.0 2.58 -2 V A dB MHz dB mA mA V V TA = 25C, Note 5 12 VDD 18V TMIN TA TMAX, Note 1 TA = 25C, VRT/CT = 2V, Note 1 VRT/CT peak to peak 7.7 47 53 0.2 0.04 8.4 1.9 9.0 59 1.0 kHz % %/C mA Vp-p TA = 25C, IO = 1mA 12V VDD 18V, IO = 5A 1 IO 20mA Note 1 Line, Load, Temp., Note 1 10Hz f 10kHz, TA = 25C, Note 1 TA = 125C, 1000 hrs., Note 1 -30 4.82 50 5 -80 25 -180 4.90 5.00 2 1 0.2 5.18 5.10 20 25 V mV mV mV/C V V mV mA Test Conditions Min Typ Max Units
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Parameter Current Sense Gain MaximumThreshold PSRR Input Bias Current Delay to Output Output RDS(ON) High RDS(ON) Low Rise Time Fall Time Undervoltage Lockout Start Threshold MIC38C42A/4A MIC38C43A/5A Minimum Operating Voltage MIC38C42A/4A MIC38C43A/5A Pulse Width Modulator Maximum Duty Cycle MIC38C42A/3A MIC38C44A/5A Minimum Duty Cycle Total Standby Current Start-Up Current VDD = 13V for MIC38C42A/44A VDD = 7.5V for MIC38C43A/45A VFB = VISNS = 0V 100 94 46 96 50 13.5 7.8 8 7.0 14.5 8.4 9 7.6 ISOURCE = 200mA ISINK = 200mA TA = 25C, CL = 1nF TA = 25C, CL = 1nF 20 11 40 30 Notes 2, 3 VCOMP = 5V, Note 2 12 VDD 18V, Note 2 2.85 0.9 3.0 1 70 -0.1 120 Test Conditions Min Typ
Micrel, Inc.
Max Units
3.15 1.1
V/V V dB
-2 250
A ns
80 60 ns ns
15.5 9.0 10 8.2
V V V V
% % 0 %
230
A mA
Operating Supply Current
4.0
6.0
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= VPIN1 ; 0 VTH (ISNS ) 0.8V VTH (ISNS )
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.
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MIC38C42A/43A/44A/45A
Micrel, Inc.
Typical Characteristics
Oscillator Frequency Configuration
100
OUTPUT DEAD TIME (%)
RT RESISTANCE (k)
200pF 470pF 1nF
100 VDD = 15V
OSC. DISCHARGE CURRENT (mA)
MIC38C42/43 Output Dead Time vs. Oscillator Frequency
Oscillator Discharge Current vs. Temperature
9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 VDD = 15V VOSC = 2V 7.2 7.0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
4.7nF 10 10nF 200pF 470pF 1nF 18nF 1 1x104 1x105 FREQUENCY (Hz) 1x106
10 1.8nF 4.7nF 10nF VDD = 15V
1 1x104 1x105 5x105 OSCILLATOR FREQUENCY (Hz)
CURRENT SENSE AMP THRESHOLD (V)
1.2 1.0 125C 0.8 0.6 25C 0.4 0.2 0.0 -50C
VREF SHORT CURCUIT CURRENT (mA)
Current Sense Amplifier vs. Error Amplifier Output
Short-Circuit Reference Current vs. Temperature
120 OUTPUT VOLTAGE (V) 100 80 60 40 20 VDD = 15V 25 20 15 10 5 0 -5 -10 -15 0.0
MIC38C4x Output Waveform
VD = 15V CL = 1nF 0.2 0.4 0.6 TIME (s) 0.8 1.0
0 2 4 6 8 ERROR AMPLIFIER OUTPUT (V)
0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
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Micrel, Inc. mended. 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 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 capacitor 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 50A (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 0.1F 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-
VIN 26V to 40V
CT1
Q1 IRF820
VOUT 12V, 2A
R1 10 1/2W C2 1000pF L1 48H 31DQ10 D1 C3 3.3F C4 0.1F
R2 68k
D4 1N765B
0.1F*
MKS2
D2 M17Z105 1/4W
C5 4.7F
4.7
6.8k 0.22F
0.1F
100k
1
MIC38C42A
D3 MBR030
COMP VREF FB ISNS VDD OUT
8 7 6 5
2 3 4
D5
T1 C8 0.1F
1N4001
6.19k 1% 1.62k 1%
R4 18
RT/CT GND
C7 200pF
R5 16k
0.1F
*Locate near MIC38C42 supply pins
Figure 1. 500kHz, 25W, Buck Converter
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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. L1 is wound on a Siemens N49 EFD core.
Test Line Regulation Conditions VIN = 26V to 80V, IO = 2A Results 0.5% 0.6% 90% 100mV Symbol CT1 T1 L1 Custom Coil1 4923 4924 4925 ETS2
Micrel, Inc.
ETS 92420 ETS 92419 ETS 92421
Load Regulation VIN = 48V, IO = 0.2A to 2A Efficiency VIN = 48V, IO = 2A Output Ripple VIN = 48V, IO = 2A (20MHz BW)
1. Custom Coils, Alcester, SD tel: (605) 934-2460 2. Energy Transformation Systems, Inc. tel: (415) 324-4949.
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
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 (5m) 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.
10k
0.15F 0.1F
NC
MIC5022
VDD
0.1F
SMP60N06-14
5m
GATEH VB GATEL SH+
SH- SL+
35H
VOUT 5V, 8A
FLT EN
IN
6.8k
300k
47k
4.7nF
MIC38C43A
COMP VREF
470F 25V
NC
4.3k
FB ISNS
2200 pF
VDD VOUT GND
1000F Low ESR
NC
CT
RT/CT
3.3k
0.1F* MKS2
10k
*Locate near the MIC38C43 supply pins.
GND
SL-
Figure 2. 100kHz, Synchronous Buck Converter
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MIC38C42A/43A/44A/45A
Micrel, Inc.
Package Information
0.026 (0.65) MAX)
PIN 1
0.157 (3.99) 0.150 (3.81)
DIMENSIONS: INCHES (MM)
0.050 (1.27) TYP
0.020 (0.51) 0.013 (0.33) 0.0098 (0.249) 0.0040 (0.102) 0-8 SEATING PLANE 45 0.010 (0.25) 0.007 (0.18)
0.064 (1.63) 0.045 (1.14)
0.197 (5.0) 0.189 (4.8)
0.050 (1.27) 0.016 (0.40) 0.244 (6.20) 0.228 (5.79)
8-Pin SOP (M)
0.122 (3.10) 0.112 (2.84)
0.199 (5.05) 0.187 (4.74)
DIMENSIONS: INCH (MM)
0.120 (3.05) 0.116 (2.95) 0.036 (0.90) 0.032 (0.81) 0.043 (1.09) 0.038 (0.97) 0.012 (0.30) R
0.007 (0.18) 0.005 (0.13)
0.012 (0.03) 0.0256 (0.65) TYP
0.008 (0.20) 0.004 (0.10)
5 MAX 0 MIN
0.012 (0.03) R 0.039 (0.99) 0.035 (0.89) 0.021 (0.53)
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 Micrel for any damages resulting from such use or sale. (c) 2002 Micrel Incorporated
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