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LTC3026 Datasheet(PDF) 10 Page - Linear Technology |
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LTC3026 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 18 page  LTC3026 0 3026fd operaTion Figure 1. Output Load Step Response LDO Operation An undervoltage lockout comparator (UVLO) senses the BST pin voltage to ensure that the bias supply for the LDO is greater than 4.2V before enabling the LDO. If BST is below 4.2V, the UVLO shuts down the LDO, and OUT is pulled to GND through the external divider. The LDO provides a high accuracy output capable of supplying 1.5A of output current with a typical dropout voltage of only 100mV. A single ceramic capacitor as small as 10µF is all that is required for output bypassing. A low reference voltage allows the LTC3026 output to be programmed to much lower voltages than available in common LDOs (range of 0.4V to 2.6V). The devices also include current limit and thermal over- load protection, and will survive an output short-circuit indefinitely. The fast transient response of the follower output stage overcomes the traditional trade-off between dropout voltage, quiescent current and load transient response inherent in most LDO regulator architectures, see Figure 1. Figure 2. Soft-Start with Boost Disable Figure 3. Programming the LTC3026 the LDO reference voltage from 0V to 0.4V over a period of approximately 200µs, see Figure 2. IOUT 1.5A 0mA OUT AC 20mV/DIV 100µs/DIV VOUT = 1.5V COUT = 10µF VIN = 1.7V VB = 5V 3026 F01 SHDN OUT PG HI LO 100µs/DIV TA = 25°C ROUT = 1 VIN = 1.7V VB = 5V 1.5V 1.5V 0V 0V 3026 F02 VOUT ADJ GND COUT R2 R1 LTC3026 3026 F03 VOUT 0.4V 1 R2 R1 The LTC3026 also includes a soft-start feature to prevent excessive current flow at VIN during start-up. When the LDO is enabled, the soft-start circuitry gradually increases Adjustable Output Voltage The output voltage is set by the ratio of two external resis- tors as shown in Figure 3. The device servos the output to maintain the ADJ pin voltage at 0.4V (referenced to ground). Thus, the current in R1 is equal to 0.4V/R1. For goodtransientresponse,stabilityandaccuracythecurrent in R1 should be at least 80µA, thus, the value of R1 should be no greater than 5k. The current in R2 is the current in R1 plus the ADJ pin bias current. Since the ADJ pin bias current is typically <10nA it can be ignored in the output voltage calculation. The output voltage can be calculated using the formula in Figure 3. Note that in shutdown the output is turned off and the divider current will be zero once COUT is discharged. |
Similar Part No. - LTC3026_1 |
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Similar Description - LTC3026_1 |
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