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 50µA typical and
operating current has been reduced to 4.0 mA typical. De-
creased output rise and fall times drive larger MOSFETs, and
rail-to-rail output capability increases efficiency, especially at
lower supply voltages. The MIC38C4x also features a trimmed
oscillator discharge current and bandgap reference.
The MIC38C4x denotes 8-pin plastic DIP and SOIC 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.
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
Functional Diagram
VDD
7 (12)
*
35V
5V
Reference
Oscillator
T
Q
‡
VREF
8 (14)
UVLO
†
(VD)
(11)
RT/CT
4 (7)
OUT
6 (10)
2 (3)
FB
2.5V
2R
R
S
R
(PGND)
Q
(8)
*
COMP
1 (1)
*
†
( )
pins
GND* (AGND) ISNS
5
(9)
3 (5)
‡
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
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
July 2005
1
M9999-072805
MICREL [ MICREL SEMICONDUCTOR ]
