ltc1751 Linear Technology Corporation, ltc1751 Datasheet
ltc1751
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ltc1751 Summary of contents
Page 1
... PGOOD pin on the LTC1751-3.3 and LTC1751-5 indicates when the output voltage has reached its final value and if the output has an undervoltage fault condition. The FB pin of the adjustable LTC1751 can be used to program the desired output voltage or current. An optional soft-start capacitor may be used at the SS pin to prevent excessive inrush current during start-up ...
Page 2
... OUT GND 4 MS8 PACKAGE 8-LEAD PLASTIC MSOP T = 150 C, JMAX *PGOOD ON LTC1751-3.3/LTC1751 LTC1751 Consult factory for parts specified with wider operating temperature ranges. The denotes specifications which apply over the full specified = FLY IN CONDITIONS ...
Page 3
... Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Based on long term current density limitations. Note 3: The LTC1751EMS8-X is guaranteed to meet performance specifications from Specifications over the – operating temperature range are assured by design, characterization and correlation with statistical process controls ...
Page 4
... OUT 0.001 0.01 0.1 LOAD CURRENT (mA) Start-Up SHDN 2V/DIV PGOOD 5V/DIV V OUT 1V/DIV C = 10nF 2ms/DIV SS 1751 G06 (LTC1751-5) Output Voltage vs Output Current 5 FLY 5.1 5.0 V 4.9 4 OUTPUT CURRENT (mA) 4 Short-Circuit Output Current vs Input Voltage 250 200 V = 2.75V ...
Page 5
... PGOOD pulls low. PGOOD may be pulled up through an external resistor to any appropri- ate reference level. FB (Pin 1) (LTC1751): The voltage on this pin is compared to the internal reference voltage (1.205V) by the error comparator to keep the output in regulation. An external resistor divider is required between V gram the output voltage ...
Page 6
... V IN GND FB V OUT V IN GND 6 W LTC1751-3.3/LTC1751-5 READY + – – – + – + UNDERV + 2 COMP1 – CHARGE PUMP 3 4 LTC1751 COMP1 – CHARGE PUMP REF CONTROL 7 SHDN + 6 C – 1751 BD1 REF CONTROL ...
Page 7
... CMOS input with a threshold voltage of approxi- mately 0.8V. The LTC1751 is in shutdown when a logic low is applied to the SHDN pin. The quiescent supply current of the LTC1751 will be slightly higher if the SHDN pin is driven high with a voltage that is below V driven all the way to V ...
Page 8
... Flying Capacitor Selection Warning: A polarized capacitor such as tantalum or aluminum should never be used for the flying capacitor since its voltage can reverse upon start-up of the LTC1751. Low ESR ceramic capacitors should always be used for the flying capacitor. The flying capacitor controls the strength of the charge pump ...
Page 9
... SS For example, with a 4.7nF capacitor the 10% to 90% rise time will be approximately 2.8ms. If the output charge storage capacitor then the average output current for an LTC1751-5 will be 4V/2.8ms • 14mA, giving 28mA at the V pin. IN The soft-start feature is optional. If there is no capacitor on SS, the output voltage of the LTC1751 will ramp up as quickly as possible ...
Page 10
... Programming the LTC1751 Output Voltage (FB Pin) While the LTC1751-3.3/LTC1751-5 versions have internal resistive dividers to program the output voltage, the programmable LTC1751 may be set to an arbitrary voltage via an external resistive divider. Since it employs a voltage doubling charge pump not possible to achieve output voltages greater than twice the available input voltage ...
Page 11
... BAT54C 7 LTC1540 4 – 10k HYST – OUT + LTC1751-3.3 7 OFF SHDN PGOOD GND 1nF 4 1751 TA06 = 1.205V OUT IN 1751 TA07 Si4435DY OUT I 100mA OUT 10 F 100k 1 HIGH = BACKUP MODE ...
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... McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear-tech.com – OUT C2 LTC1751 17ms SHDN GND C3 680pF U Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) ...