STMicroelectronics E-UC3842BN

Overview

E-UC3842BN from STMicroelectronics is a high-performance current-mode PWM controller IC designed for fixed-frequency off-line and DC-DC power supplies. It features a trimmed oscillator (250 kHz guaranteed), latching PWM for cycle-by-cycle current limiting, 5 V ±1% internal reference, under-voltage lockout (16 V on / 10 V off), and a totem-pole output capable of ±1 A peak drive current - enabling direct N-channel MOSFET gate driving in flyback, forward, and boost converters.

For engineers reviewing the E-UC3842BN datasheet, E-UC3842BN pinout, E-UC3842BN application, or E-UC3842BN equivalent, key selection considerations include UVLO threshold compatibility with bulk input voltage rails, duty cycle range (up to 96%), oscillator programming flexibility (RT/CT), current sense gain (3 V/V), and thermal limits in Minidip package (100 °C/W junction-to-ambient).

Technical Context

The E-UC3842BN implements current-mode control using an internal error amplifier, PWM latch, and comparator that compares sensed inductor current against the error amp output. Its oscillator uses RT/CT timing components to set frequency up to 500 kHz, with discharge current trimmed to 7.5–8.8 mA for stable ramp generation.

UVLO hysteresis ensures reliable start-up and brown-out recovery, while the 5 V reference provides precise biasing for both CT charging and feedback divider networks. The output stage operates in push-pull configuration with low saturation voltage (<0.4 V at 20 mA sink) and fast rise/fall times (50–150 ns into 1 nF), supporting high-efficiency switching at up to 96% duty cycle.

Key Specifications

Pinout & Package

E-UC3842BN is supplied in an 8-pin Minidip (PDIP-8) package with 0.3-inch body width and through-hole mounting. Pin 5 serves as the common ground for analog and power sections; pin 7 (Vi) accepts 10–30 V unregulated input; pin 6 delivers high-current gate drive.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar current-mode PWM controller applications.

Compared with UC3842D8, E-UC3842BN offers superior thermal margin in through-hole designs but requires larger board area; versus TL494CN, it delivers simpler current-mode implementation with built-in fault protection but lacks dual-output flexibility.

Availability

E-UC3842BN is available at Aetrix Electronics and suitable for AC-DC adapters, flyback SMPS, and industrial DC-DC converters requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for E-UC3842BN includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, microcontroller, power, and sensor solutions for automotive, industrial, and consumer markets.

E-UC3842BN belongs to the UC384x family of current-mode PWM controllers, developed specifically for cost-sensitive, high-reliability off-line and isolated DC-DC power conversion where simplicity, robustness, and cycle-by-cycle fault protection are essential.

FAQ

What is the maximum recommended operating temperature for E-UC3842BN in Minidip package?

The junction operating temperature range is –40°C to +150°C. With a thermal resistance of 100 °C/W (Minidip), sustained power dissipation above 1.25 W at 25°C ambient requires heatsinking or airflow. Derating begins at 25°C ambient, reaching zero allowable dissipation at 150°C junction temperature.

Can E-UC3842BN be used in continuous conduction mode (CCM) flyback designs?

Yes - E-UC3842BN supports CCM flyback operation when combined with slope compensation injected at the ISENSE pin (pin 3). The internal 1 V threshold and 3 V/V gain allow precise peak-current control; external RC network on COMP (pin 1) stabilizes loop dynamics per Figure 21A in the datasheet.

How does the RT/CT network affect maximum duty cycle?

Maximum duty cycle is determined by the ratio of RT to CT and oscillator discharge current. For E-UC3842BN, increasing RT raises frequency but reduces max duty cycle; decreasing CT increases frequency and extends duty cycle. Figure 5 shows D_max vs. RT at fixed CT = 3.3 nF, ranging from ~94% to 100%.

Is external soft-start required, and how is it implemented?

Soft-start is optional but recommended to limit inrush current. It is implemented by connecting a capacitor from COMP (pin 1) to ground, charged via a current source (e.g., 1 mA from VREF through 5 kΩ). This gradually raises the error amp output, ramping up duty cycle from zero - see Figure 24 in the datasheet.