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 50µA
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.
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 (100µA 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
April 2005
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M9999-042205
MIC38C42A/43A/44A/45A
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 MM8™ (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.
April 2005
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M9999-042205
MIC38C42A/43A/44A/45A
Micrel, Inc.
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
) ....................... –65°C to +150°C
Operating Ratings
Junction Temperature (T
J
) ........................................ 150°C
Package Thermal Resistance
8-Pin MM8™
(θ
JA
) ............................................. 250°C/W
8-Pin SOIC
(θ
JA
) ............................................... 170°C/W
Electrical Characteristics
(Note 6)
V
DD
= 15V,
Note 4;
R
T
= 11.0k; C
T
= 3.3nF; –40°C
≤
T
A
≤
85°C; 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
A
VOL
Unity Gain Bandwidth
PSRR
Output Sink Current
Output Source Current
V
OUT
High
V
OUT
Low
V
COMP
= 2.5V
V
FB
= 5.0V
2
≤
V
O
≤
4V
Note 1
12
≤
V
DD
≤
18V
V
FB
= 2.7V, V
COMP
= 1.1V
V
FB
= 2.3V, V
COMP
= 5V
V
FB
= 2.3V, R
L
= 15k to ground
V
FB
= 2.7V, R
L
= 15k to V
REF
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
µA
dB
MHz
dB
mA
mA
V
V
T
A
= 25°C,
Note 5
12
≤
V
DD
≤
18V
T
MIN
≤
T
A
≤
T
MAX
,
Note 1
T
A
= 25°C, V
RT/CT
= 2V,
Note 1
V
RT/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
T
A
= 25°C, I
O
= 1mA
12V
≤
V
DD
≤
18V, I
O
= 5µA
1
≤
I
O
≤
20mA
Note 1
Line, Load, Temp.,
Note 1
10Hz
≤
f
≤
10kHz, T
A
= 25°C,
Note 1
T
A
= 125°C, 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
µV
mV
mA
Test Conditions
Min
Typ
Max
Units
M9999-042205
4
April 2005
MIC38C42A/43A/44A/45A
Parameter
Current Sense
Gain
MaximumThreshold
PSRR
Input Bias Current
Delay to Output
Output
R
DS(ON)
High
R
DS(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
V
DD
= 13V for MIC38C42A/44A
V
DD
= 7.5V for MIC38C43A/45A
V
FB
= V
ISNS
= 0V
100
94
46
96
50
13.5
7.8
8
7.0
14.5
8.4
9
7.6
I
SOURCE
= 200mA
I
SINK
= 200mA
T
A
= 25°C, C
L
= 1nF
T
A
= 25°C, C
L
= 1nF
20
11
40
30
Notes 2, 3
V
COMP
= 5V,
Note 2
12
≤
V
DD
≤
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
µA
ns
Ω
Ω
80
60
ns
ns
15.5
9.0
10
8.2
V
V
V
V
%
%
0
%
230
µA
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 V
EA
= 0.
Note 3:
Gain defined as:
A =
∆
V
PIN1
;
0
≤
V
TH
(I
SNS
)
≤
0.8V
V
TH
(I
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.
April 2005
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M9999-042205
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