Accept the challenge of power IC requirements and easily achieve precisely regulated supply voltage!
LDO regulators usually require hardware modifications to adjust the output voltage, but if the specifications are constantly changing, changing the board and components may increase development time. In such applications, LDO regulators with software programmable output voltage can save time and cost.
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The LT3072 dual 2.5 A linear regulator meets the challenging needs of digital IC power supplies by providing hardware-independent output voltage regulation even when the LT3072 is powered from a pre-regulator input supply. The LT3072 features UltraFast™ transient response and a low dropout voltage of 80 mV, making it easy to generate precisely regulated supply voltages when the load changes rapidly.
Only 10 μF (1 μF + 2.2 μF + 6.8 μF) of output capacitance is required to achieve the low output noise of 12 μV rms and ultrafast transient response of the LT3072. Low noise is critical for communication or sensor circuits to maintain their high performance.
The LT3072 integrates two fully independent 2.5 A LDO regulators in a single package. The LT3072's 0.6 V to 2.5 V output voltage range is wide enough to power a variety of digital IC rails. Several three-state pins on the LT3072 allow the output voltage of each channel to be programmed, which can be easily accomplished with jumpers, a microcontroller, or a power system management (PSM) IC.
Figure 1 shows the LT3072 in a standalone circuit for digital IC loads with stringent power requirements. An important component of tight power specifications is the ability to respond quickly to load transients, as shown in the LT3072’s ultrafast transient response curve in Figure 2.
Figure 1. The ultrafast load transient response, 12 μV rms output noise, and 80 mV dropout of the dual-channel 2.5 A LT3072 meet the needs of digital ICs with stringent power requirements. The schematic shows that the three-state V O1B2–0 and V O2B2–0 pins, OUT1 and OUT2, are fixed at 2.5 V and 0.6 V, respectively, but simply changing the state on these pins changes the output voltage, allowing software control of the LT3072 without time-consuming and expensive hardware modifications.
Figure 2. The LT3072’s single-output ultrafast transient response shows that microsecond settling time can be achieved with only 10 μF (1 μF + 2.2 μF + 6.8 μF) of output capacitance. The center trace shows that additional capacitance can be used to limit the excursion amplitude, but with slightly longer settling time.
Each output value is set by three three-state pins: V O1B2 , V O1B1 , V O1B0 , V O2B2 , V O2B1 , V O2B0 . Each three-state pin is set by grounding, floating, or applying a voltage to it. In this way, the output can be set from 0.6 V to 2.5 V.
In addition to setting the nominal programming voltage, the programmed output voltage can be adjusted by ±10% through the input margin setting. The corresponding input voltage can be as low as 200 mV, above or slightly above the 2.5 V and 0.6 V output voltages, in order to optimize the transient response performance margin. The output voltage status is indicated by the PWRGD pin, and there are pins for analog monitoring of the output current, and the ±7% accurate output current limit value can also be set. There are also pins for analog monitoring of the die temperature.
The LT3072 dynamically controls the output of the switch preceding it. This allows instantaneous adjustment of the LDO regulator’s output voltage while keeping its input voltage at a level that maintains high efficiency and fast load transient response.
The preregulator supply for the LT3072 in Figure 3 uses the LT8616. This is a 42 V, dual-channel 1.5 A/2.5 A synchronous monolithic step-down regulator. This setup accepts a single 3.6 V to 42 V system input voltage range. In this solution, the programmable output range of OUT1 of the LT3072 is 0.6 V to 1.8 V. The OUT1 channel uses VIOC to control the corresponding LT8616 output, allowing the LDO regulator to operate in the optimal efficiency and transient response transition range. OUT1 can be dynamically adjusted between 0.6 V and 1.8 V using the V O1B2-1 pin.
Figure 3. IN1 and IN2 of the LT3072 are preregulated by the dual, step-down LT8616. The connection between VOIC1 of the LT3072 and TR/SS1 of the LT8616 allows the LT3072 to dynamically preregulate its IN1 input for excellent efficiency and load transient performance, while allowing the output voltage of the LT3072 to be adjusted without hardware changes.
The current limit of the OUT1 linear regulator channel is set to 1.8 A, slightly higher than the 1.5 A maximum output current of the LT8616 Channel 1. OUT2 is fixed at 0.6 V and can be 2.5 A using the 3 A current limit.
The LT3008-3.3 provides bias current to the LT3072. The PG2 (power good) pin of the LT8616 provides a slight delay before the LT3072 starts up. Figure 4 shows the LT3072 dynamically controlling the switch channel that preregulates the LDO regulator input.
Figure 4. Dynamic testing of the circuit shown in Figure 3. The trace shows how software changes to the three-state pins V O1B2 and V O1B1 (V O1B0 is tied to ground) enable adjustment of the LT3072’s OUT1 voltage. In turn, the LT3072 dynamically controls the LT8616 Channel 1 output, which preregulates the LDO regulator’s IN1 input. This maintains the LDO regulator’s IN1 voltage at a fixed dropout above the LDO regulator’s OUT1, resulting in high efficiency and high load transient performance, all without any hardware changes.
The LT3072 dual-channel LDO regulator for digital IC power has two low noise channels and ultra-fast load transient response characteristics. The two output voltages can be set by setting a few three-state pins without the use of resistors. When the input power supply to the LT3072 is a pre-regulator, the LT3072 VIOC function can be used to control the input power supply, allowing dynamic changes in output voltage programming without affecting transient response performance or efficiency.
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