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MIC38C44 Schematic ( PDF Datasheet ) - Micrel Semiconductor

Teilenummer MIC38C44
Beschreibung BiCMOS Current-Mode PWM Controllers
Hersteller Micrel Semiconductor
Logo Micrel Semiconductor Logo 




Gesamt 11 Seiten
MIC38C44 Datasheet, Funktion
MIC38C42/3/4/5
Micrel, Inc.
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 50µAtypical
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.
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
For fast rise and fall times and higher output drive, refer to
the MIC38HC4x.
Functional Diagram
VDD
7 (12)
VREF
8 (14)
RT/CT
4 (7)
FB
2 (3)
2.5V
35V
5V
Reference
Oscillator
2R
R
UVLO
*
T Q
S
R
Q
(VD)
(11)
OUT
6 (10)
(PGND)
(8)
*
COMP GND* (AGND) ISNS
1 (1)
5 (9) 3 (5)
( ) pins 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
September 2007
1
M9999-091107
http://www.Datasheet4U.com






MIC38C44 Datasheet, Funktion
MIC38C42/3/4/5
Typical Characteristics
Oscillator Frequency
Configuration
100
200pF
470pF
1nF
10
1.8nF
4.7nF
10nF
VDD = 15V
1
1x104
1x105
5x105
OSCILLATOR FREQUENCY (Hz)
Current Sense Amplifier
vs. Error Amplifier Output
1.2
1.0
125°C
0.8
0.6
25°C
0.4
-50°C
0.2
0
02468
ERROR AMPLIFIER OUTPUT (V)
Micrel, Inc.
MIC38C42/43 Output Dead Time
vs. Oscillator Frequency
100
VDD = 15V
4.7nF
10
10nF
200pF
470pF
1nF
1
1x104
18nF
1x105
FREQUENCY (Hz)
1x106
Short-Circuit Reference
Current vs. Temperature
120
100
80
60
40
20 VDD = 15V
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
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
7.2 VOSC = 2V
7.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
MIC38C4x
Output Waveform
25
20
15
10
5
0
-5 VD = 15V
-10 CL = 1nF
-15
0.0 0.2 0.4 0.6 0.8 1.0
TIME (µs)
M9999-091107
6 September 2007
http://www.Datasheet4U.com

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