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LTC1439CGW Datasheet(PDF) 11 Page - Linear Technology |
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LTC1439CGW Datasheet(HTML) 11 Page - Linear Technology |
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11 / 32 page  11 LTC1438/LTC1439 OPERATION the AUXDR pin is above 9.5V to allow regulated 12V VPP supplies to be easily implemented. When AUXDR is below 8.5V an external feedback divider may be used to set other output voltages. Taking the AUXON pin low shuts down the auxiliary regulator providing a convenient logic- controlled power supply. The AUX block can be used as a comparator having its inverting input tied to the internal 1.19V reference. The AUXDR pin is used as the output and requires an external pull-up to a supply of less than 8.5V in order to inhibit the invoking of the internal resistive divider. INTVCC/ EXTVCC Power Power for the top and bottom MOSFET drivers and most of the other LTC1438/LTC1439 circuitry is derived from the INTVCC pin. The bottom MOSFET driver supply is also connected to INTVCC. When the EXTVCC pin is left open, an internal 5V low dropout regulator supplies INTVCC power. If EXTVCC is taken above 4.8V, the 5V regulator is turned off and an internal switch is turned on to connect EXTVCC to INTVCC. This allows the INTVCC power to be derived from a high efficiency external source such as the output of the regulator itself or a secondary winding, as described in the Applications Information section. (Refer to Functional Diagram) Frequency Synchronization A Phase-Locked Loop (PLL) is available on the LTC1439 to allow the oscillator to be synchronized to an external source connected to the PLLIN pin. The output of the phase detector at the PLL LPF pin is also the control input of the oscillator, which operates over a 0V to 2.4V range corresponding to – 30% to 30% in frequency. When locked, the PLL aligns the turn-on of the top MOSFET to the rising edge of the synchronizing signal. When PLLIN is left open, PLL LPF goes low, forcing the oscillator to minimum frequency. Power-On Reset The POR2 pin is an open drain output which pulls low when the main regulator output voltage of the second controller is out of regulation. When the output voltage rises to within 7.5% of regulation, a timer is started which releases POR2 after 216 (65536) oscillator cycles. This function is not available on the LTC1438X. Auxiliary Linear Regulator The auxiliary linear regulator in the LTC1439 controls an external PNP transistor for operation up to 500mA. A precise internal AUXFB resistive divider is invoked when |
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