UC3846 Standard Switching Power Supply Controller Features Automatic Feedforward Compensation

Programmable pulse-by-pulse current limit

Automatic Symmetry Correction in Push-Pull Configurations

Enhanced load response characteristics

Parallel Operation Capability of Modulator Power Systems

Differential Current Sense Amplifier with Common Mode Range

double pulse suppression

200 mA totem pole output

±2% bandgap reference

undervoltage lockout

Soft start capability

stop terminal
500KHz operation

Internal block diagram

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The UC3846 control chip provides all the necessary functions to implement a fixed frequency, current mode control scheme while maintaining a minimum external part count. The superior performance of this technology can be measured by improved line regulation, enhanced load response characteristics, and design of simple control loops. Topological advantages include inherent pulse-by-pulse current limiting capability, automatic symmetry correction of push-pull converters, and the ability to parallel “power modules” while maintaining equal current sharing. In addition to the soft-start function, protection circuits include built-in undervoltage lockout and programmable current limit. A shutdown function is also available, which can initiate a complete shutdown or power down with an automatic restart. Other features include fully latched operation, dual-pulse rejection, dead-time adjustment capability, and a ±2% trimmed bandgap reference. The UC3846 has a low output in the shutdown state.

4. The current into pin 1 is guaranteed to lock the circuit in the shutdown state.

5. The current into pin 1 is guaranteed not to lock up the circuit in the shutdown state.

6. These parameters, although guaranteed under recommended operating conditions, have not been 100% tested in production.

Output dead time (Td)
figure 1. UC3846 oscillator circuit

The output dead time is determined by an external capacitor, according to the formula: Tdus()=145CT(μF)——Right T-type(Thousand 8486 ;)– ------------- --------

The formula is: fT(KHz)=R-------------------------------(KΩ)CT(μF)-T type 2.2

figure 2. Error Amplifier Output Configuration

image 3. Parallel operation

Figure 4. Pulse-by-Pulse Current Limiting

Figure 5. Current Sense Amplifier Connections

In some applications, a small PC filter may be required to reduce switching transients on the differential input, allowing long-range noise-free sensing.

Mechanical Dimensions

pack

16 - Inclination