Can KT6368A Bluetooth chip directly connect to 5V MCU level? Or 1.8V, 3.3V MCU?

First, let's describe the level situation of KT6368A Bluetooth chip:

Check KT6368A's power supply: supports 2.6V-3.3V supply voltage [recommended 3.3V]. This means the chip's IO voltage also changes with the supply voltage. For example: if the supply voltage is 2.5V, then KT6368A's high level voltage is 2.5V



Next, facing customer application scenarios, there are three cases:
Case 1: Customer's MCU GPIO is 3.3V TTL level
1.Then it's recommended to directly connect with 100 ohm resistors in series, including both RX and TX, all should be connected with resistors
2.The purpose of this resistor is actually not for level matching, but to prevent current backflow, must add it, don't connect directly


Case 2: Customer's MCU GPIO is 1.8V TTL level
This can choose direct connection, or choose to connect with 100 ohm resistors in series, both TX and RX


Case 3: Customer's MCU GPIO is 5V TTL level
1. Then it's recommended to directly connect with 1K resistors in series, including both RX and TX, all should be connected with resistors
2. The purpose of this resistor is for voltage reduction, must add it, don't connect directly

3. At this time, if the customer's MCU IO drive capability is strong, after connecting resistors, the level reaching KT6368A's pin 7 may still be 3.7V. Then this resistor can be increased to 2K, both are fine, because different MCUs have different drive capabilities, hard to explain uniformly

4. Of course customers can also choose dedicated level conversion chips, if they accept the cost

5. Of course customers can also choose discrete components to do level conversion, there are many reference resources available online



Finally, the principle is still to save where possible
Today's chips are actually quite strong, whether in performance, cost, or durability

According to our extensive customer production experience, basically for 5V levels, connecting with 1K resistors can achieve normal mass production, very stable

Actually although the chip's IO is marked as 3.3V, strictly speaking level conversion is recommended

But considering practical applications, directly connecting with 1K resistor is no problem

The chip's IO port can also withstand 5V voltage, as long as the drive current isn't too large, then it's OK, it won't affect communication, nor affect lifespan



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