MIC38C42/3/4/5
Micrel
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. Decreased output rise and fall times drive larger
MOSFETs, and rail-to-rail output capability increases effi-
ciency, especially at lower supply voltages. The MIC38C4x
also features a trimmed oscillator discharge current and
bandgap reference.
MIC38C4x denotes 8-pin plastic DIP, SOIC, and MM8™
packages. MIC38C4x-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 performance 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)
*
35V
5V
Reference
UVLO
†
VREF
8 (14)
(VD)
(11)
RT/CT
4 (7)
Oscillator
T
Q
‡
OUT
6 (10)
FB
2 (3)
2R
2.5V
R
S
R
Q
(PGND)
(8)
*
COMP
1 (1)
GND*(AGND)
5
(9)
ISNS
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
MM8 is a trademark of Micrel, Inc.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
August 2000
1
MIC38C42/3/4/5
MICREL [ MICREL SEMICONDUCTOR ]
