MIC38C42/3/4/5 Micrel, Inc.
September 2007 1 M9999-091107
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 efficiency, espe-
cially at lower supply voltages. The MIC38C4x also features
a trimmed oscillator discharge current and bandgap refer-
ence.
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 14-
pin 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.
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
T Q
S
RQ
R
2R
Oscillator
UVLO
5V
Reference
VDD
7 (12)
VREF
8 (14)
RT/CT
4 (7)
FB
2 (3)
2.5V
COMP
1 (1)
GND* (AGND)
5 (9)
ISNS
3 (5)
OUT
6 (10)
( ) pins are on MIC38C4x-1 (14-lead) versions only
*MIC38C4x, (8-lead) versions only
(VD)
(11)
(PGND)
(8)
35V
*
*
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
MIC38C42/3/4/5 Micrel, Inc.
M9999-091107 2 September 2007
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
Ordering Information
Part Number* Temperature Range Package
Standard Pb-Free
MIC38C42BN MIC38C42YN -40°C to +85°C 8-pin Plastic DIP
MIC38C43BN MIC38C43YN -40°C to +85°C 8-pin Plastic DIP
MIC38C44BN MIC38C44YN -40°C to +85°C 8-pin Plastic DIP
MIC38C45BN MIC38C45YN -40°C to +85°C 8-pin Plastic DIP
MIC38C42-1BN Contact Factory -40°C to +85°C 14-pin Plastic DIP
MIC38C43-1BN Contact Factory -40°C to +85°C 14-pin Plastic DIP
MIC38C44-1BN MIC38C44-1YN -40°C to +85°C 14-pin Plastic DIP
MIC38C45-1BN Contact Factory -40°C to +85°C 14-pin Plastic DIP
MIC38C42BM MIC38C42YM -40°C to +85°C 8-pin SOIC
MIC38C43BM MIC38C43YM -40°C to +85°C 8-pin SOIC
MIC38C44BM MIC38C44YM -40°C to +85°C 8-pin SOIC
MIC38C45BM MIC38C45YM -40°C to +85°C 8-pin SOIC
MIC38C42BMM MIC38C42YMM -40°C to +85°C 8-pin MSOP
MIC38C43BMM MIC38C43YMM -40°C to +85°C 8-pin MSOP
MIC38C44BMM MIC38C44YMM -40°C to +85°C 8-pin MSOP
MIC38C45BMM MIC38C45YMM -40°C to +85°C 8-pin MSOP
MIC38C42-1BM MIC38C42-1YM -40°C to +85°C 14-pin SOIC
MIC38C43-1BM MIC38C43-1YM -40°C to +85°C 14-pin SOIC
MIC38C44-1BM MIC38C44-1YM -40°C to +85°C 14-pin SOIC
MIC38C45-1BM MIC38C45-1YM -40°C to +85°C 14-pin SOIC
* Refer to the Part Number Cross Reference for a listing of Micrel devices equivalent to UC284x and UC384x devices.
MIC38C42/3/4/5 Micrel, Inc.
September 2007 3 M9999-091107
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.
1
2
3
4
8
7
6
5
COMP
FB
ISNS
RT/CT
V R E F
VDD
OUT
GND
MIC38C4x
2NC NC13
3FB VDD12
4NC VD
11
5ISNS OUT
10
6NC AGND
9
7RT/CT PGND
8
1COMP V R E F14
MIC38C4x-1
8-Pin DIP (N)
8-Pin SOIC (M)
8-Pin MSOP (MM)
14-Pin DIP (-1BN)
14-Pin SOIC (-1BM)
Pin Configuration
MIC38C42/3/4/5 Micrel, Inc.
M9999-091107 4 September 2007
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 2 20 mV
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 5 25 mV
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 –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 –0.5 –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
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 JA) .......................................125°C/W
8-Pin MSOP JA) ..............................................250°C/W
8-Pin SOIC JA) ................................................170°C/W
14-Pin Plastic DIP JA) ......................................90°C/W
14-Pin SOIC JA) ..............................................145°C/W
MIC38C42/3/4/5 Micrel, Inc.
September 2007 5 M9999-091107
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 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) IDD = 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:
∆VPIN1
A = ; 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 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, Inc.
M9999-091107 6 September 2007
Typical Characteristics
1
10
100
1x1041x1055x105
RT RESISTANCE (kΩ)
OSCILLATOR FREQUENCY (Hz)
Oscillator Frequency
Configuration
10nF
4.7nF
1nF
470pF
200pF
1.8nF
VDD = 15V
1
10
100
1x1041x1051x106
OUTPUT DEAD TIME (%)
FREQUENCY (Hz)
MIC38C42/43 Output Dead Time
vs. Oscillator Frequency
VDD = 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
VDD = 15V
VOSC = 2V
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
0
20
40
60
80
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
5
10
15
20
25
0.0 0.2 0.4 0.6 0.8 1.0
OUTPUT VOLTAGE (V)
TIME (µs)
MIC38C4x
Output Waveform
VD= 15V
CL= 1nF
MIC38C42/3/4/5 Micrel, Inc.
September 2007 7 M9999-091107
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 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 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.
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.
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 (typi-
cal) 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 transistors 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 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 controllers supply
VDD (or VD for ‘-1’ versions) and ground connections. Film
type capacitors, such as Wima MKS2, are recommended.
Figure 1. 500kHz, 25W, Buck Converter
VOUT
12V, 2A
COM P
F B
I S N S
RT/CT GND
OUT
VDD
V R E F
C2
1000pF
R1
10
1/2W 31DQ10
D1
L1 48µH
C3
3.3µF C4
0.1µF
6.19k
1%
1.62k
1%
R4
18
C7
200pF
R5
16k 0.1µF
D3
MBR030
C8
0.1µF
T1
6.8k
0.22µF
100k
Q1
IRF820
0.1µF
C5
4.7µF
R2
68k
D2
M17Z105
1/4W
D5
1N4001
D4
1N765B
VIN
26V to 40V
CT1
4.7
MIC38C42
1
2
3
4
8
7
6
5
0.1µF*
*Locate near MIC38C42 supply pins
MKS2
MIC38C42/3/4/5 Micrel, Inc.
M9999-091107 8 September 2007
Symbol Custom Coil1 ETS2
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 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 MOS-
FET 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 recti-
fier. 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
0.1µFSMP60N06-14
VDD
V R E F
GND
COM P
VO U T
RT/CT
F B
I S N S
4.7nF
10k
10k
6.8k
47k
3.3k
2200
pF
470µF
25V
MIC5022
VB
G A T E H
SH+
G A T E L
SH
SL+
CT
GND
E N
FLT
VDD
+12V
5m
0.1µF*
MKS2
*Locate near the MIC38C43 supply pins.
NC
NC
IN
NC
S L
MIC38C42/3/4/5 Micrel, Inc.
September 2007 9 M9999-091107
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)
14-Pin Plastic DIP (N)
MIC38C42/3/4/5 Micrel, Inc.
M9999-091107 10 September 2007
8-Pin SOIC (M)
8-Pin MSOP (MM)
MIC38C42/3/4/5 Micrel, Inc.
September 2007 11 M9999-091107
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.
© 2000 Micrel Incorporated
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