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UCC28811DG4 Datasheet(PDF) 7 Page - Texas Instruments |
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UCC28811DG4 Datasheet(HTML) 7 Page - Texas Instruments |
7 / 34 page BLOCK DESCRIPTION BLOCK DIAGRAM 1 2 5 6 7 8 3 4 40 kW 5 pF + + + x x K 2.5 V 2.3 V + + OVP Enable 2.7/2.5 V g M VEA 0.67/0.57 V 0.23/0.15 V Current Sense Comparator S Q Q R + Restart Timer + V REF and Bias Reg V REF Init. Bias 1.7/1.4 V UVLO V REF GOOD OVP VSENSE EAOUT VINS ISENSE TZE GND GDRV VDD REF Zero Energy Detect UDG-08130 75 mV Current Reference Generator UVLO and Reference Circuit Error Amplifier UCC28810 UCC28811 www.ti.com.............................................................................................................................................................................................. SLUS865 – OCTOBER 2008 This circuitry generates a precision reference voltage used to obtain a tightly controlled UVLO threshold. In addition to generating a 2.5-V reference for the noninverting terminal of the gM amplifier, it generates the reference voltages for OVP, enable, zero energy detect and the current reference generator circuits. An internal rail of 7.5 V is also generated to drive all the internal circuitry. The voltage error amplifier in the UCC2881x is a transconductance amplifier with a typical transconductance value of 90 µS. The advantage in using a transconductance amplifier is that the inverting input of the amplifier is solely determined by the external resistive-divider from the output voltage and not the transient behavior of the amplifier itself. This allows the VSENSE pin to be used for sensing over voltage conditions. The sink and source capability of the error amplifier is approximately 10 µA during normal operation of the amplifier. But when the VSENSE pin voltage is beyond the normal operating conditions (VVSENSE >1.05 × VREF, VVSENSE < 0.88 × VREF), additional circuitry to enhance the slew-rate of the amplifier is activated. Enhanced slew-rate of the compensation capacitor results in a faster start-up and transient response. This prevents the output voltage from drifting too high or too low, which can happen if the compensation capacitor were to be driven by the normal drive current of 10- µA. When VSENSE rises above the normal range, the enhanced sink current capability increases to 1 mA, nominal. When VSENSE falls below the normal range, the UCC28810 can source more than 1 mA and the UCC28811 sources approximately 300 µA. The limited source current in the UCC28811 helps to gradually increase the error voltage on the EAOUT pin preventing a step increase in line current. The actual rate of increase of the voltage on the EAOUT pin is dependent on the compensation network externally connected to the EAOUT pin. Copyright © 2008, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Link(s): UCC28810 UCC28811 |
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