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 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.
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 (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
TQ
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
