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MIC38C42/3/4/5
Micrel, Inc.
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 50A 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. The MIC38C4x denotes 8-pin plastic DIP, SOIC, and MSOP packages. MIC384Cx-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 perfomance and power dissipation. 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 (50A 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
Functional Diagram
VDD
7 (12)
*
35V
5V Reference
Oscillator
T Q
VREF
8 (14)
UVLO
(VD)
(11)
RT/CT
4 (7)
OUT
6 (10)
2 (3)
FB 2.5V
2R R
S R
(PGND)
Q
(8)
*
COMP
1 (1) * ( ) pins
GND* (AGND) ISNS
5 (9) 3 (5)
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
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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Micrel, Inc. 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 -40C to +85C -40C to +85C -40C to +85C -40C to +85C -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 Plastic DIP 8-pin Plastic DIP 8-pin Plastic DIP 8-pin Plastic DIP 14-pin Plastic DIP 14-pin Plastic DIP 14-pin Plastic DIP 14-pin Plastic DIP 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin SOIC 8-pin MSOP 8-pin MSOP 8-pin MSOP 8-pin MSOP 14-pin SOIC 14-pin SOIC 14-pin SOIC 14-pin SOIC
Ordering Information
Part Number* Standard MIC38C42BN MIC38C43BN MIC38C44BN MIC38C45BN MIC38C42-1BN MIC38C43-1BN MIC38C44-1BN MIC38C45-1BN MIC38C42BM MIC38C43BM MIC38C44BM MIC38C45BM MIC38C42BMM MIC38C43BMM MIC38C44BMM MIC38C45BMM MIC38C42-1BM MIC38C43-1BM MIC38C44-1BM MIC38C45-1BM Pb-Free MIC38C42YN MIC38C43YN MIC38C44YN MIC38C45YN Contact Factory Contact Factory MIC38C44-1YN Contact Factory MIC38C42YM MIC38C43YM MIC38C44YM MIC38C45YM MIC38C42YMM MIC38C43YMM MIC38C44YMM MIC38C45YMM MIC38C42-1YM MIC38C43-1YM MIC38C44-1YM MIC38C45-1YM
* Refer to the Part Number Cross Reference for a listing 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 MIC38C43 MIC38C45 Startup 14.5V Minimum Operating 9V MIC38C42 MIC38C44
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Pin Configuration
MIC38C4x-1
COMP 1 14 V R E F
NC
2
3
4
13 N C
12 VDD
11 VD
10 OUT
9
8
MIC38C4x
COMP 1 FB
FB
8 7 6 5
VREF VDD OUT GND
NC
2
ISNS 5
NC 6
ISNS 3 RT/CT 4
AGND
P GND
RT/CT 7
8-Pin DIP (N) 8-Pin SOIC (M) 8-Pin MSOP (MM)
14-Pin DIP (-1BN) 14-Pin SOIC (-1BM)
Pin Description
Pin Number N, M, MM 1 Pin Number -1BN, -1BM 1 2 2 3 4 3 5 6 4 5 8 9 6 10 11 7 12 13 8 14 7 Pin Name COMP NC FB NC ISNS NC RT/CT GND PGND AGND OUT VD VDD NC VREF Pin Function Compensation: Connect external compensation network to modify the error amplifier output. Not internally connected. Feedback (Input): Error amplifier input. Feedback is 2.5V at desired output voltage. Not internally connected. Current Sense (Input): Current sense comparator input. Connect to current sensing resistor or current transformer. Not internally connected. Timing Resistor/Timing Capacitor: Connect external RC network to select switching frequency. Ground: Combined analog and power ground. Power Ground: N-channel driver transistor ground. Analog Ground: Controller circuitry ground. Power Output: Totem-pole output. Power Supply (Input): P-channel driver transistor supply input. Return to power ground (PGND). Analog Supply (Input): Controller circuitry supply input. Return to analog ground (AGND). Not internally connected. 5V Reference (Output): Connect external RC network.
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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)......................... -65C to +150C
Operating Ratings
Junction Temperature (TJ) ......................................... 150C Package Thermal Resistance 8-Pin Plastic DIP (JA) .......................................125C/W 8-Pin MSOP (JA) ..............................................250C/W 8-Pin SOIC (JA) ................................................170C/W 14-Pin Plastic DIP (JA) ......................................90C/W 14-Pin SOIC (JA) ..............................................145C/W
Electrical Characteristics
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 -0.5 5 14 -1 6.8 0.1 1.1 2.42 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, Note 6 TMIN TA TMAX, Note 1 TA = TMIN to TMAX TA = 25C, VRT/CT = 2V 7.7 7.2 49 52 0.2 0.04 8.4 8.4 1.9 9.0 9.5 55 1.0 kHz % %/C mA mA Vp-p TA = 25C, IO = 1mA 12V VDD 18V, IO = 5A, Note 6 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
VRT/CT peak to peak
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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 Minimum Operating Voltage Pulse Width Modulator Maximum Duty Cycle Minimum Duty Cycle Total Standby Current Start-Up Current Operating Supply Current Zener Voltage (VDD) VDD = 13V for MIC38C42/44 VFB = VISNS = 0V IDD = 25mA, Note 6 30 50 4.0 37 MIC38C42/3 MIC38C44/5 94 46 96 50 MIC38C42/4 MIC38C43/5 MIC38C42/4 MIC38C43/5 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 3.15 1.1 -2 250 Units V/V V dB A ns 80 60 15.5 9.0 10 8.2 ns ns V V V V % % 0 200 6.0 % A mA V
VDD = 7.5V for MIC38C43/45
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: VPIN1 ; 0 VTH (ISNS) 0.8V A= 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 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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Typical Characteristics
Oscillator Frequency Configuration
OUTPUT DEAD TIME (%)
200pF 470pF
VDD = 15V
OSC. DISCHARGE CURRENT (mA)
100
RT RESISTANCE (k)
100
MIC38C42/43 Output Dead Time vs. Oscillator Frequency
9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2
Oscillator Discharge Current vs. Temperature
1nF
10
1.8nF 4.7nF 10nF
VDD = 15V
10
4.7nF
10nF
1nF
200pF
470pF
18nF
VDD = 15V VOSC = 2V
1 1x104 1x105 5x105 OSCILLATOR FREQUENCY (Hz)
1 1x104
1x105 FREQUENCY (Hz)
1x106
7.0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
CURRENT SENSE AMP THRESHOLD (V)
1.2 1.0 0.8 0.6 0.4 0.2
VREF SHORT CURCUIT CURRENT (mA)
Current Sense Amplifier vs. Error Amplifier Output
120 100 80 60 40 20
Short-Circuit Reference Current vs. Temperature
OUTPUT VOLTAGE (V)
25 20 15 10 5 0 -5 -10 -15 0.0
MIC38C4x Output Waveform
125C
25C
-50C
VDD = 15V
VD = 15V CL = 1nF
0
0 2 4 6 8 ERROR AMPLIFIER OUTPUT (V)
0 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
0.2
0.4 0.6 TIME (s)
0.8
1.0
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Micrel, Inc. 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. Magnetic components are carefully chosen for minimal loss at 500kHz. CT1 and T1 are wound on Magnetics, Inc. Ptype material toroids. L1 is wound on a Siemens N49 EFD core.
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 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 recommended.
V IN 26V to 40V
CT1
Q1 IRF820
D4 1N765B
VOUT 12V, 2A
R1 10 1/2W C2 1000pF L1 48H 31DQ10 D1 C3 3.3F C4 0.1F
R2 68k
0.1F*
MKS2
D2 M17Z105 1/4W
C5 4.7F
4.7
6.8k 0.22F
0.1F
100k
1 2 3
MIC38C42
D3 MBR030
COM P V R E F FB ISNS VDD OU T
8 7 6 5
D5
T1 C8 0.1F
1N4001
6.19k 1% 1.62k 1%
R4 18
4
RT/CT GND
C7 200pF
R5 16k
0.1F
*Locate near MIC38C42 supply pins
Figure 1. 500kHz, 25W, Buck Converter
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Test Line Regulation Efficiency Conditions VIN = 26V to 80V, IO = 2A Results 0.5% 0.6% 90% 100mV Symbol CT1 T1 L1
1. 2.
Micrel, Inc.
Custom Coil1 4923 4924 4925 ETS2 ETS 92420 ETS 92419 ETS 92421
Load Regulation VIN = 48V, IO = 0.2A to 2A Output Ripple VIN = 48V, IO = 2A (20MHz BW) VIN = 48V, IO = 2A
Custom Coils, Alcester, SD tel: (605) 934-2460 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.
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 highside current sense inputs to provide overcurrent protection. Refer to the MIC5020, MIC5021, and MIC5022 data sheets for more information.
+12V
10k
0.15F 0.1F
MIC5022
0.1F
SMP60N06-14
VDD
GATEH VB GATEL SH+
5m
35H
NC
6.8k
300k
FL T EN
V OUT 5V, 8A
4.7nF
MIC38C43
COM P V R E F FB ISNS VDD VOUT GND
NC
470F 25V
4.3k
IN NC
CT
1000F Low ESR
47k
SH- SL+
2200 pF 3.3k
RT/CT
0.1F* MKS2
GND
10k
S L-
*Locate near the MIC38C43 supply pins.
Figure 2. 100kHz, Synchronous Buck Converter
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Micrel, Inc.
Package Information
PIN 1 DIMENSIONS: INCH (MM)
0.380 (9.65) 0.370 (9.40)
0.135 (3.43) 0.125 (3.18)
0.255 (6.48) 0.245 (6.22) 0.300 (7.62) 0.013 (0.330) 0.010 (0.254)
0.018 (0.57) 0.100 (2.54)
0.130 (3.30) 0.0375 (0.952)
0.380 (9.65) 0.320 (8.13)
8-Pin Plastic DIP (N)
.770 (19.558) MAX PIN 1
.235 (5.969) .215 (5.461)
.060 (1.524) .045 (1.143) .160 MAX (4.064) .310 (7.874) .280 (7.112) .080 (1.524) .015 (0.381) .015 (0.381) .008 (0.2032) .160 (4.064) .100 (2.540) .110 (2.794) .090 (2.296) .060 (1.524) .045 (1.143) .023 (.5842) .015 (.3810) .400 (10.180) .330 (8.362)
14-Pin Plastic DIP (N)
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Micrel, Inc.
8-Pin SOIC (M)
8-Pin MSOP (MM)
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MIC38C42/3/4/5
Micrel, Inc.
14-Pin SOIC (M)
MICREL INC.
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
2180 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
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) 2000 Micrel Incorporated
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