The back-to-back MOSFETs Q1-A and Q1-B are both connected to the V(IN1) (5V) supply, while Q3-A and Q3-B are connected to the V(IN2) (3.3V) supply. This design choice is made to prevent the internal diodes from being shorted to the 5V and 3.3V supplies. The Gate1 pin of the LTC1645 controls Q3-A and Q3-B, whereas the Gate2 pin controls Q1-A and Q1-B. The ON pin has a turn-on threshold voltage of 0.8V for Gate1 and 2.0V for Gate2. The undervoltage lockout thresholds for the V(CC1) and V(CC2) pins are 2.3V and 1.2V, respectively. Given that the circuit in Figure 1 employs two supply voltages, there are two potential scenarios:
Figure 2: V(GATE2) and V(OUT_HOT_SWAP) pin voltages are increased to 12V and 15V, respectively.
In this setup, the LTC1645 plays a critical role in managing the switching operations between the two supply voltages. The back-to-back configuration of the MOSFETs ensures a smooth transition between the 5V and 3.3V supplies without causing any unintended short circuits or current spikes. This arrangement is particularly useful in applications where multiple voltage levels need to be managed efficiently and safely.
Furthermore, the undervoltage lockout thresholds help protect the system from operating below optimal voltage levels, which could lead to instability or damage. By setting these thresholds at 2.3V for V(CC1) and 1.2V for V(CC2), the circuit ensures reliable operation across a wide range of input conditions. The turn-on thresholds for the ON pin further refine the control mechanism, allowing precise timing of when each MOSFET should activate based on the specific gate voltage requirements.
Additionally, the ability to adjust the V(GATE2) and V(OUT_HOT_SWAP) pin voltages to higher values such as 12V and 15V demonstrates the flexibility of the circuit design. This feature can be particularly beneficial in systems that require higher output voltages for certain components or stages. Overall, this configuration not only enhances the efficiency and reliability of the power management system but also provides robust protection against potential faults and malfunctions.
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