【Introduction】The LTC3626 with current and temperature monitoring is a high efficiency, monolithic synchronous step-down switching regulator capable of delivering 2.5A maximum output current from an input voltage of 3.6V to 20V (circuit shown in figure 1). The LTC3626 employs a unique controlled on-time/constant frequency, current-mode architecture, making it ideal for low duty cycle applications and high frequency operation while providing fast response to load transients (see Figure 2) . In addition, the device has mode setting, tracking and synchronization functions. The LTC3626’s 3mm x 4mm package has very low thermal impedance and can operate without an external heat sink, even when delivering maximum power to the load.
Figure 1: 20V Max Input, 2.5A, 2MHz Step-Down Regulator with Current and Temperature Monitoring
Figure 2: Load Step Response of the Circuit of Figure 1
In addition to its excellent regulation capabilities, the LTC3626’s current and temperature monitoring capabilities are even more prominent. They provide monitoring and control with minimal additional components.
Output/input current detection
The LTC3626 senses the output current by synchronizing the switch during the on-time of the switch, andOUT A proportional current (in 1/16000) is drawn on the pin. In Figure 3, by placing IMONOUTThe measured output of the pin is compared to the calculated value, showing the IMONOUTthe accuracy of the output. The error remains below 1% over most of the output current range.
Figure 3: Output Current vs. Output Current Monitor Current
Similarly, combining this same sense current signal with the duty cycle of the buck regulator canIN A current proportional to the input current is generated at the pin (again at 1/16000). An accuracy of better than 5% is achieved over a wide current range (see Figure 4).
Figure 4: Input Current vs. Input Current Monitor Current
Both current signals are connected to an internal voltage amplifier referenced to 1.2V, which shuts down the device when triggered. Therefore, simply connect a separate resistor to IMONIN or IMONOUT pin (shown in Figure 1), the input and output current limits can be set. The relationship between the current limit and the resistor is:
For example: a 10k resistor will set a current limit of about 2A.
This simple scheme provides monitoring and active control of the input and output current limits, which can be accomplished with external control circuitry such as a DAC and a few passive components.
The LTC3626 generates a voltage proportional to its own die temperature, which can be used to set the maximum temperature limit. At room temperature, the temperature monitor pin (TMON) is typically 1.5V. To calculate the chip temperature TJthe T can beMONThe voltage is multiplied by the temperature monitor voltage-to-temperature conversion factor of 200°K/V, and the offset of 273°C is subtracted. In addition, the LTC3626 also has a temperature limit comparator, set by the temperature limit pins TSET and TMONA pin feeds it a signal. So, by giving TSET Applying a voltage to the pin sets the maximum temperature limit according to:
Choosing a maximum temperature limit of 125°C is equivalent to TSET With a setpoint of approximately 2V on the pin, the IC will be at the die temperature TJ Immediate shutdown when this limit is reached.
The LTC3626 combines current and temperature monitoring with a high performance buck regulator in a compact package. A microprocessor or other external control logic can implement condition monitoring through easy-to-use input and output current and temperature monitor pins, and the device can also be programmed with a threshold voltage on the temperature set limit pins. achieve its own shutdown.
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