KCC's Quizzes AQQ305 about a mutual exponentiation equation
1. Quote of the month: "A train station is where a train stops. A bus station is where a bus stops. I have a work station on my desk, so..." - unknown
2. Quiz AQQ305 about finding a mutual exponential equation
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Quiz: How Well Do You Know Adaptive Power Switching?
Is your I/O module overheating? The AD74416H's Adaptive Power Switching (APS) can cut heat dissipation by up to 40% — but how well do you really understand how it works?
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LTC3878
Production
The LTC3878 is a synchronous step-down switching DC/DC controller optimized for high switching frequency and fast transient response. The constant on-time...
Datasheet
LTC3878 on Analog.com
LTC7803
Recommended for New Designs
The LTC7803 is a high performance, 100% Duty Cycle Capable, synchronous step-down DC/DC switching regulator controller that drives an all N-channel power...
Datasheet
LTC7803 on Analog.com
Hi,
We are doing a 214kHz Buck with 24vin and 15vout at 3a(out).(as attached in LTspice)
Using the LTC3878.
-Though it needs a 10 Meg resistor into its RON pin in order to give the 214kHz.
That means a current of just 2.3uA.
Surely using a 10 MEG resistor to set the switching frequency is asking for trouble? (with noise)
LTC3878LTC3878 BUCK.asc
Hello,
Per the figure below the on-time is a linear function of the ION current for ION currents over the 1uA to 100uA range. Therefore, even though an ION current of 2.3uA is on the lower end of this range, the on-time should follow the formulas in the data sheet.
I am not aware of cases where a low ION current has caused a noise issue, but it is a valid concern, especially if the layout is noisy. In case noise is an issue, add an optional footprint for a capacitor from the ION pin to the chip’s SGND pin as done on the standard demo board (DC1292A), see below. If used, the value should be about 1nF or lower.
The LTC3878 is an older generation valley current mode controller. It does not have a built in clock like other current mode controllers. Therefore, its switching frequency will vary slightly over-load and frequency. This is true for an ION current of any value. For tight control of the frequency, consider a fixed frequency current mode controller such as the LTC7803 (Vin: 4.5V to 40V, Vout: up to 40V, 100% duty cycle capable) or similar controller.
Best regards,
Mike
