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LT1942 Datasheet(PDF) 7 Page - Linear Technology |
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LT1942 Datasheet(HTML) 7 Page - Linear Technology |
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7 / 16 page  LT1942 7 1942fb PI FU CTIO S PGND23 (Pin 1): Power Ground for VOFF and VON Switcher. Tie directly to local ground plane. SW3 (Pin 2): Switch Pin for VON Switcher. This is the collector of an internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. D3 (Pin 3): Output of VON Switcher. Place output decoup- ling capacitor from this pin to local ground plane. VOUT3 (Pin 4): Collector of Internal Output Disconnect PNP Transistor for the VON Switcher. Place a capacitor from this pin to local ground plane of at least 0.1 µF. FB3 (Pin 5): Feedback Pin for VON Switcher. Reference voltage is 1.25V. Connect resistive divider tap here. Minimize trace area at FB3. Set VOUT3 according to VOUT3 = 1.25(1 + R5/R6). NFB2 (Pin 6): Feedback Pin for VOFF Switcher. Reference voltage is –150mV. Connect resistive divider tap here. Minimize trace area at NFB2. Set VOUT2 according to VOUT2 = (– 0.15)(1 + R3/R4). SHDN (Pin 7): Shutdown. Tie to 1V or greater to enable the part. Tie to 0.4V or lower to disable. This pin is the global shutdown pin for all four switching regulators. CTRL4 (Pin 8): Shutdown for the LED Switcher. Tie to 0.25V or greater to enable the LED switcher. Tie to 0.1V or lower to disable. CTRL4 can also override the default 200mV reference for the LED switcher. If CTRL4 is tied to 2.5V or greater, the reference voltage is 200mV. If CTRL4 is less than 2.5V, the LED reference voltage is approximately VCTRL4/10. This allows an 8:1 dimming range for the LEDs. Refer to the Applications Section for more information. CT (Pin 9): Programmable Delay for the TFT Supplies. Place a capacitor from this pin to local ground plane. After the delay, the output disconnect PNP for the VON supply is turned on. The delay time is initiated when AVDD reaches 97% of its final value. AGND (Pin 10): Analog Ground. Tie directly to local ground plane. SS1 (Pin 11): Soft-Start Pin for AVDD Switcher. Place a soft-start capacitor from this pin to ground. Upon start-up, 3 µA of current charges the capacitor to 1.25V. Use larger capacitor for slower start-up. Leave floating if not in use. SS4 (Pin 12): Soft-Start for LED Switcher. Place a soft- start capacitor from this pin to ground. Upon start-up, 3 µA of current charges the capacitor to 1.25V. Use larger capacitor for slower start-up. Leave floating if not in use. PGOOD (Pin 13): Power Good Indication for AVDDSwitcher. Open-collector NPN. Stays open until the VFB1 voltage reaches 97% of target value at which point the pin will pull down. FB1 (Pin 14): Feedback Pin for AVDD Switcher. Connect resistive divider tap here. Minimize trace area at FB1. Set VOUT1 according to VOUT1 = 1.25(1 + R1/R2). FB4 (Pin 15): Feedback Pin for LED Switcher. Place a resistor from this node to ground. Choose R7 to set LED current (ILED) according to the following formula: if VCTRL4 ≥ 2.5V, R7 = 0.2/ILED In this case, ILED is the total LED current. If two strings of LEDs are used, ILED is the sum of the current in the two strings. If only a single string of LEDs is used, ILED is simply the single string current. For dimming LED current, drive VCTRL4 to a lower voltage. See the Applications Section for more information. D4 (Pin 16): Output of LED Switcher. Place output de- coupling capacitor from this pin to local ground plane. LED2 (Pin 17): Second Input of Current Mirror for an LED String. Connect the negative end of second string of LEDs to this pin. If not in use, leave floating. |
Similar Part No. - LT1942_15 |
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Similar Description - LT1942_15 |
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