Current Mode Pwm Controller UC3844AM Integrated Circuit Components

CURRENT MODE PWM CONTROLLER

DESCRIPTION

The UC184xA family of control ICs provides all the necessary features to implement off-line fixed-frequency, current-mode switching power supplies with a minimum of external components. The current mode architecture demonstrates improved load regulation, pulse-by-pulse current limiting and inherent protection of the power supply output switch. The IC includes: A bandgap reference trimmed to ±1% accuracy, an error amplifier, a current sense comparator with internal clamp to 1V, a high current totem pole output stage for fast switching of power MOSFET's, and an externally programmable oscillator to set frequency and maximum duty cycle. The undervoltage lock-out is designed to operate with 250µA typ. start-up current, allowing an efficient bootstrap supply voltage design. Available options for this family of products, such as start-up voltage hysteresis and duty cycle, are summarized below in the Available Options section. The UC184xA family of control ICs is also available in 14-pin SOIC package which makes the Power Output Stage Collector and Ground pins available.

PRODUCT HIGHLIGHT

KEY FEATURES

• LOW START-UP CURRENT. (0.5mA max.)
• TRIMMED OSCILLATOR DISCHARGE CURRENT. (See Product Highlight)
• OPTIMIZED FOR OFF-LINE AND DC-TO-DC CONVERTERS.
• AUTOMATIC FEED FORWARD COMPENSATION.
• PULSE-BY-PULSE CURRENT LIMITING.
• ENHANCED LOAD RESPONSE CHARACTERISTICS.
• UNDER-VOLTAGE LOCKOUT WITH HYSTERESIS.
• DOUBLE PULSE SUPPRESSION.
• HIGH-CURRENT TOTEM POLE OUTPUT.
• INTERNALLY TRIMMED BANDGAP REFERENCE.
• 500KHz OPERATION.
• LOW R_O ERROR AMPLIFIER.

 APPLICATIONS

■ ECONOMICAL OFF-LINE FLYBACK OR FORWARD CONVERTERS.

■ DC-DC BUCK OR BOOST CONVERTERS.

■ LOW COST DC MOTOR CONTROL.

ABSOLUTE MAX IMUM RAT INGS (Note 1)

Supply Voltage (Low Impedance Source) (VCC) ......................................................... 30V

Supply Voltage (ICC < 30mA).......................................................................... Self Limiting

Output Current ............................................................................................................. ±1A

Output Energy (Capacitive Load)................................................................................. 5µJ

Analog Inputs (VFB & ISENSE) ........................................................................ -0.3V to +6.3V

Error Amp Output Sink Current ............................................................................... 10mA

Power Dissipation at TA = 25°C (M Package) .............................................................. 1W

Storage Temperature Range .................................................................... -65°C to +150°C

Lead Temperature (Soldering, 10 Seconds) ............................................................. 300°C

Note 1. Exceeding these ratings could cause damage to the device. All voltages are with respect

            to Ground. Currents are positive into, negative out of the specified terminal. Pin numbers

            refer to DIL packages only.

PACKAGE PIN OUTS                                          THERMAL DATA

Junction Temperature Calculation: T_J = T_A + (P_D x θ_JA).

The θ_JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow