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L6911E Fiches technique(PDF) 6 Page - STMicroelectronics |
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L6911E Fiches technique(HTML) 6 Page - STMicroelectronics |
6 / 20 page L6911E 6/20 VCC =12V VCC =5V Switching frequency variations vs. RT are reported in Fig.1. Note that forcing a 50 µA current into this pin, the device stops switching because no current is delivered to the oscillator. Figure 1. Digital to Analog Converter The built-in digital to analog converter allows the adjustment of the output voltage from 1.050V to 1.825V with 25mV binary steps as shown in the previous table 1. The internal reference is trimmed to ensure the precision of 1%. The internal reference voltage for the regulation is programmed by the voltage identification (VID) pins. These are TTL compatible inputs of an internal DAC that is realised by means of a series of resistors rpoviding a par- tition of the internal voltage reference. The VID code drives a multiplexer that selects a voltage on a precise point of the divider. The DAC output is delivered to an amplifier obtaining the VPROG voltage reference (i.e. the set-point of the error amplifier). Internal pull-ups are provided (realized with a 5 µA current generator); in this way, to program a logic ”1” it is enough to leave the pin floating, while to program a logic ”0” it is enough to short the pin to GND. The voltage identification (VID) pin configuration also sets the power-good thresholds (PGOOD) and the over- voltage protection (OVP) thresholds. Soft Start and Inhibit At start-up a ramp is generated charging the external capacitor CSS by means of a 10µA constant current, as shown in figure 2. When the voltage across the soft start capacitor (VSS) reaches 0.5V the lower power MOS is turned on to dis- charge the output capacitor. As VSS reaches 1V (i.e. the oscillator triangular wave inferior limit) also the upper f S 200kH z 4.306 10 7 ⋅ R T k Ω () ----------------------------- + = f S 200k H z 15 10 7 ⋅ R T k Ω () -------------------- + = 10 10 0 1000 Fr equency [ kH z] 10 100 1000 10000 RT to G N D RT to V CC= 12 V RT to V CC= 5V |
Numéro de pièce similaire - L6911E |
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Description similaire - L6911E |
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