Zhishi Classroom [Discrete Semiconductors]——Master of Capacity Management of Electronic Devices: Power Management IC (Part 2)
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Load switch Is a space-saving integrated power switch. Most load switches consist of four pins, namely: input voltage, output voltage, enable terminal and ground. When the device is enabled through the ON pin, the pass FET is turned on, allowing current to flow from the input pin to the output pin and power is delivered to the downstream circuit.
Generally speaking, a load switch is usually connected between a power supply and a load (IC or LSI). During operation, it needs to control the on/off of the power line provided to the IC and LSI according to the system's operating mode to reduce power consumption. Load switch ICs have low power consumption and built-in functions such as undervoltage lockout, thermal shutdown, overcurrent protection, etc., which helps the system achieve integrity and reliability.
(1) Undervoltage lockout (UVLO)
UVLO is a protection mode when the supply voltage is lower than the IC's turn-on threshold voltage. When the input voltage drops below a specified value, this function puts the IC into standby mode, thereby avoiding internal circuit failures and allowing the circuit to operate stably.
(2) Thermal shutdown (TSD)
TSD is a circuit that prevents device degradation and destruction due to significant ambient temperature rise, and prevents heating of the device itself due to unexpected large current loads, etc. When the internal temperature detection circuit detects a specified temperature, the output transistor is turned off.
(3) True reverse current blocking
True reverse current blocking means that when the input voltage V IN is higher than the output voltage V OUT , current flows back from the V OUT pin to the V IN pin. Preventing reverse current protects the power supply connected to the V IN terminal from degradation and destruction.
(4) Overcurrent limitation
Overcurrent limiting is a function to protect the module power supply or load when the output terminal V OUT has overcurrent or short circuit, etc. It can prevent the electrical appliance from being damaged by high current.
(5) Conversion rate control drive circuit
This circuit will suppress the surge current generated during the switching transient process and prevent the electronic equipment from being damaged by excessive surge current at the moment of startup.
(6) Output discharge
In a general load switch circuit, when the output transistor is turned off, the terminal voltage of V OUT can be maintained for a certain time according to the load capacitance connected to the output terminal. This circuit can quickly discharge the charge accumulated on the load side and reduce the V OUT terminal voltage to around IC GND.
The above three-part knowledge of power management IC ends here. In the first two parts, we focused on (Part 1): Basic classification of power management ICs and (Part 2): Composition of power management systems , and focused on introducing the basic working principles and related functions of four major categories of products: linear regulators, switching regulators, LDOs, and load switches. I believe that those who read carefully will definitely gain a lot from it~
Please continue to pay attention to #芝识课堂 in the future , we will bring you more detailed semiconductor design knowledge and skills.
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