MIC38C42A/43A/44A/45A
Micrel, Inc.
April 2005
1
M9999-042205
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 effi-
ciency, 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 MSOP-
8 (MM8) package options
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
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
T
Q
S
R
Q
R
2R
Oscillator
UVLO
5V
Reference
VDD
7
VREF
8
RT/CT
4
FB
2
2.5V
COMP
1
GND
5
ISNS
3
OUT
6
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
MIC38C42A/43A/44A/45A
Micrel, Inc.
M9999-042205
2
April 2005
Ordering Information
Part Number
Temperature
Standard
Pb-Free
Range
Package
MIC38C42ABM
MIC38C42AYM
40C to +85C
8-pin SOIC
MIC38C43ABM
MIC38C43AYM
40C to +85C
8-pin SOIC
MIC38C44ABM
MIC38C44AYM
40C to +85C
8-pin SOIC
MIC38C45ABM
MIC38C45AYM
40C to +85C
8-pin SOIC
MIC38C42ABMM
MIC38C42AYMM
40C to +85C
8-pin MM8TM
MIC38C43ABMM
MIC38C43AYMM
40C to +85C
8-pin MM8TM
MIC38C44ABMM
MIC38C44AYMM
40C to +85C
8-pin MM8TM
MIC38C45ABMM
MIC38C45AYMM
40C to +85C
8-pin MM8TM
UVLO Thresholds
Startup 8.4V
Startup 14.5V
Duty Cycle
Minimum Operating 7.6V
Minimum Operating 9V
0% to 96%
MIC38C43A
MIC38C42A
0% to 50%
MIC38C45A
MIC38C44A
Selection Guide
Refer to the Part Number Cross Reference for a listings of Micrel devices equivalent to UC284x and UC384x devices.
MIC38C42A/43A/44A/45A
Micrel, Inc.
April 2005
3
M9999-042205
Pin Description
Pin Number
Pin Name
Pin Function
1
COMP
Compensation: Connect external compensation network to modify the error
amplifier output.
2
FB
Feedback (Input): Error amplifier input. Feedback is 2.5V at desired output
voltage.
3
ISNS
Current Sense (Input): Current sense comparator input. Connect to current
sensing resistor or current transformer.
4
RT/CT
Timing Resistor/Timing Capacitor: Connect external RC network to select
switching frequency.
5
GND
Ground: Combined analog and power ground.
6
OUT
Power Output: Totem-pole output.
7
VDD
Analog Supply (Input): Controller circuitry supply input. Return to analog
ground (AGND).
8
VREF
5V Reference (Output): Connect external RC network.
1
2
3
4
8
7
6
5
COMP
FB
ISNS
RT/CT
VREF
VDD
OUT
GND
MIC38C4xA
8-Lead SOIC (M)
8-Lead MM8TM (MM)
Pin Configuration
MIC38C42A/43A/44A/45A
Micrel, Inc.
M9999-042205
4
April 2005
Electrical Characteristics
(Note 6)
V
DD
= 15V, Note 4; R
T
= 11.0k; C
T
= 3.3nF; 40C T
A
85C; unless noted
Parameter
Test Conditions
Min
Typ
Max
Units
Reference Section
Output Voltage
T
A
= 25C, I
O
= 1mA
4.90
5.00
5.10
V
Line Regulation
12V V
DD
18V, I
O
= 5A
2
20
mV
Load Regulation
1 I
O
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, T
A
= 25C, Note 1
50
V
Long Term Stability
T
A
= 125C, 1000 hrs., Note 1
5
25
mV
Output Short Circuit
30
80
180
mA
Oscillator Section
Initial Accuracy
T
A
= 25C, Note 5
47
53
59
kHz
Voltage Stability
12 V
DD
18V
0.2
1.0
%
Temp. Stability
T
MIN
T
A
T
MAX
, Note 1
0.04
%/C
Clock Ramp
T
A
= 25C, V
RT/CT
= 2V, Note 1
7.7
8.4
9.0
mA
Reset Current
Amplitude
V
RT/CT
peak to peak
1.9
Vp-p
Error Amp Section
Input Voltage
V
COMP
= 2.5V
2.4
2.50
2.58
V
Input Bias Current
V
FB
= 5.0V
0.1
2
A
A
VOL
2 V
O
4V
65
90
dB
Unity Gain Bandwidth
Note 1
0.7
1.0
MHz
PSRR
12 V
DD
18V
60
dB
Output Sink Current
V
FB
= 2.7V, V
COMP
= 1.1V
2
14
mA
Output Source Current
V
FB
= 2.3V, V
COMP
= 5V
0.3
1
mA
V
OUT
High
V
FB
= 2.3V, R
L
= 15k to ground
5
6.8
V
V
OUT
Low
V
FB
= 2.7V, R
L
= 15k to V
REF
0.1
1.1
V
Absolute Maximum Ratings
Supply Voltage (V
DD
) .................................................... 20V
Switch Supply Voltage (V
D
) .......................................... 20V
Current Sense Voltage (V
ISNS
) ..................... 0.3V to 5.5V
Feedback Voltage (V
FB
) ................................ 0.3V to 5.5V
Output Current (I
OUT
) ................................................... 0.5A
Storage Temperature (T
A
) ....................... 65C to +150C
Operating Ratings
Junction Temperature (T
J
) ........................................ 150C
Package Thermal Resistance
8-Pin MM8TM (
JA
) ............................................. 250C/W
8-Pin SOIC (
JA
) ............................................... 170C/W
MIC38C42A/43A/44A/45A
Micrel, Inc.
April 2005
5
M9999-042205
Parameter
Test Conditions
Min
Typ
Max
Units
Current Sense
Gain
Notes 2, 3
2.85
3.0
3.15
V/V
MaximumThreshold
V
COMP
= 5V, Note 2
0.9
1
1.1
V
PSRR
12 V
DD
18V, Note 2
70
dB
Input Bias Current
0.1
2
A
Delay to Output
120
250
ns
Output
R
DS(ON)
High
I
SOURCE
= 200mA
20
R
DS(ON)
Low
I
SINK
= 200mA
11
Rise Time
T
A
= 25C, C
L
= 1nF
40
80
ns
Fall Time
T
A
= 25C, C
L
= 1nF
30
60
ns
Undervoltage Lockout
Start Threshold
MIC38C42A/4A
13.5
14.5
15.5
V
MIC38C43A/5A
7.8
8.4
9.0
V
Minimum Operating Voltage
MIC38C42A/4A
8
9
10
V
MIC38C43A/5A
7.0
7.6
8.2
V
Pulse Width Modulator
Maximum Duty Cycle
MIC38C42A/3A
94
96
%
MIC38C44A/5A
46
50
%
Minimum Duty Cycle
0
%
Total Standby Current
Start-Up Current
V
DD
= 13V for MIC38C42A/44A
100
230
A
V
DD
= 7.5V for MIC38C43A/45A
Operating Supply Current
V
FB
= V
ISNS
= 0V
4.0
6.0
mA
Note 1: These parameters, although guaranteed, are not 100% tested in production.
Note 2: Parameter measured at trip point of latch with V
EA
= 0.
Note 3: Gain defined as:
A =
V
V
(I
)
0
V
(I
)
0.8V
PIN1
TH
SNS
TH
SNS
;
Note 4: Adjust V
DD
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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