UC3844B, UC3845B, UC2844B, UC2845B
High Performance Current Mode Controllers
The UC3844B, UC3845B series are high performance fixed frequency current mode controllers. They are specifically designed for Off−Line and dc−dc converter applications offering the designer a cost−effective solution with minimal external components. These integrated circuits feature an oscillator, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output ideally suited for driving a power MOSFET.
Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle−by−cycle current limiting, a latch for single pulse metering, and a flip−flop which blanks the output off every other oscillator cycle, allowing output deadtimes to be programmed from 50% to 70%.
These devices are available in an 8−pin dual−in−line and surface mount (SOIC−8) plastic package as well as the 14−pin plastic surface mount (SOIC−14). The SOIC−14 package has separate power and ground pins for the totem pole output stage.
The UCX844B has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off−line converters. The UCX845B is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).
Features
• Pb−Free Packages are Available
• Trimmed Oscillator for Precise Frequency Control
• Oscillator Frequency Guaranteed at 250 kHz
• Current Mode Operation to 500 kHz Output Switching Frequency
• Output Deadtime Adjustable from 50% to 70%
• Automatic Feed Forward Compensation
• Latching PWM for Cycle−By−Cycle Current Limiting
• Internally Trimmed Reference with Undervoltage Lockout
• High Current Totem Pole Output
• Undervoltage Lockout with Hysteresis
• Low Startup and Operating Current
MAXIMUM RATINGS
| Rating | Symbol | Value | Unit |
| Total Power Supply and Zener Current | (ICC + IZ) | 30 | mA |
| Output Current, Source or Sink (Note 1) | IO | 1.0 | A |
| Output Energy (Capacitive Load per Cycle) | W | 5.0 | μJ |
| Current Sense and Voltage Feedback Inputs | Vin | − 0.3 to + 5.5 | V |
| Error Amp Output Sink Current | IO | 10 | mA |
| Power Dissipation and Thermal Characteristics D Suffix, Plastic Package, SOIC−14 Case 751A Maximum Power Dissipation @ TA = 25°C Thermal Resistance, Junction−to−Air D1 Suffix, Plastic Package, SOIC−8 Case 751 Maximum Power Dissipation @ TA = 25°C Thermal Resistance, Junction−to−Air N Suffix, Plastic Package, Case 626 Maximum Power Dissipation @ TA = 25°C Thermal Resistance, Junction−to−Air | PD RθJA PD RθJA PD RθJA | 862 145 702 178 1.25 100 | mW °C/W mW °C/W W °C/W |
| Operating Junction Temperature | TJ | +150 | °C |
| Operating Ambient Temperature UC3844B, UC3845B UC2844B, UC2845B | TA | 0 to + 70 − 25 to + 85 | °C |
| Storage Temperature Range | Tstg | − 65 to +150 | °C |
Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit values (not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied, damage may occur and reliability may be affected.
1. Maximum package power dissipation limits must be observed.
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UC2844BD1R2G Electronic IC Chips HIGH PERFORMANCE CURRENT MODE CONTROLLERS Images
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