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ZXLB1600X10TC Datasheet(PDF) 6 Page - Zetex Semiconductors |
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ZXLB1600X10TC Datasheet(HTML) 6 Page - Zetex Semiconductors |
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6 / 16 page  Filtered PWM operation The input of an internal low pass filter is switched to VREF when the EN pin is high and switched to ground when the EN pin is low. The output of this filter drives the comparator within the control loop. A continuous high state on EN therefore provides a filtered voltage of value Vref to the comparator and the control loop regulates the output to a nominal value of 28V. However, by varying the duty cycle (D) of the EN signal at a suitably high frequency (f>10kHz), the control loop will see a voltage, that has an average value equal to the duty cycle multiplied by VREF. This provides a means of adjusting the output voltage to a lower value. It also allows the device to be both turned on and adjusted with a single signal at the 'EN' pin. The output during this mode of operation will be a dc voltage equal to D x 28V Gated PWM operation The internal circuitry of the ZXLB1600 is turned off when no signal is present on the 'EN' pin for more than 120 s (nominal). A low frequency signal applied to the EN pin will therefore gate the device 'on' and 'off' at the gating frequency and the duty cycle of this signal can be varied to provide a 'chopped' output voltage equal to D x 28V. For best accuracy, the gating frequency should be made as low as possible (e.g. below 1kHz), such that the turn off delay of the chip is only a small proportion of the gating period. Further details of setting output current are given in the application notes. Low battery detection A comparator driving an open drain NMOS output transistor performs the low battery flag function. The detection threshold (battery voltage falling) is set to 1.98V nominal with internal resistors R3 and R4, but this can be changed by shunting the internal potential divider with two external resistors at pin 'LBT'. Operation is such that the output transistor will be turned on when the battery voltage falls below the detection threshold. VBLT = 1.21 x (R3+R4)/R4 A small amount (nominal 20mV) of hysteresis is provided to aid clean switching. The low battery detection circuit remains active when 'EN' is low. ZXLB1600 ISSUE 3 - SEPTEMBER 2003 SEMICO NDUC TORS 6 |
Similar Part No. - ZXLB1600X10TC |
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Similar Description - ZXLB1600X10TC |
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