The MIC38HC4x family is a fixed frequency current mode PWM controller with 1A drive current capability. Micrel's BiCMOS device is compatible with 384x bipolar device pins. Their high output drives, with fast rise and fall times, coupled with low starting current, make them ideal PWM controllers where high efficiency is required.
Functional Diagram
The undervoltage locking circuit allows' 42 and '44 versions to start at 14.5V and run as low as 9V, and' 43 and '45 versions to start at 8.4V and run as low as 7.6V. All versions operate up to 20V. Compared to a bipolar UC384x device operating on a 15V power supply, the starting current has been reduced to 50 μa and the operating current has been reduced to 4.0 mA. Reduced output rise and fall times drive larger MOSFeTs, and rail-to-rail output capabilities improve efficiency, especially at lower supply voltages.
Pin Configuration
The MIC38HC4x also features a trimmer oscillator discharge current and band gap reference. MIC38HC4x-1 is available in 14-pin plastic DIP and SOIC packages. 8-pin devices are small in size, while 14-pin devices separate analog and power connections to improve performance and power consumption
Typical Characteristics
Features
● Fast 20ns output rise and 15ns output fall times
● - 40°C to +85°C temperature range exceeds UC284x specifications
● High-performance, low-power BiCMOS Process
● Ultralow start-up current (50µA typical)
● Low operating current (4mA typical)
● High output drive (1A peak current, HC version)
● CMOS outputs with rail-to-rail swing
● Current-mode operation up to 500kHz
● 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
