SNVAA70 june   2023 LM5176 , LM5176-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Principle of the TEC
    2. 1.2 Design Specification and Key Challenge
  5. 2Tec Driver Design Using Buck-Boost Controller
    1. 2.1 System Description
    2. 2.2 Block Diagram of TEC Design With LM5176
    3. 2.3 Output Voltage Control of LM5176
  6. 3Test Result
    1. 3.1 TEC Current Versus Output Voltage
    2. 3.2 Current Ripple Measurement Through TEC Element
    3. 3.3 Start-Up
    4. 3.4 Efficiency
  7. 4Summary
  8. 5References

Output Voltage Control of LM5176

Figure 2-2 shows the topology of the output voltage control using a microcontroller. Vout is regulated by using a resistor divider (R1 and R2) to the FB pin. The internal reference voltage of the LM5176 is 0.8 V. To control Vout through the DAC, the Resistor R3 is connected with the feedback divider and allows current to feed into the feedback node. For a detailed explanation, please refer to PMP9796 5 V Low-Power TEC Driver Reference Design.

GUID-20230508-SS0I-JG7Q-4GN0-RLM9DMNMMRR7-low.svgFigure 2-2 Control of Vout Using MCU

According to the data sheet, the bottom resistor R2 in the resistor divider is in the 1 kΩ to 100 kΩ range. Once the value of R1 has been chosen, R2 and R3 can be calculated by using the following equations:

Equation 1. R3=Vctrl_max-Vctrl_minVo_max-Vo_min×R1
Equation 2. R2=VFB×R1×R3Vo_max×R3-VFB×R1+R3+Vctrl_min×R1

where

  • R3 is the resistor between control voltage and FB pin
  • Vctrl_max is the maximum value of control voltage
  • Vctrl_min is the minimum value of control voltage
  • Vo_max is the minimum value of output voltage
  • Vo_min is the minimum value of output voltage

For example, if R1 is selected as 280 kΩ, and Vout is from 5 V to 25 V, Vctrl needs to be varied from 0.5 V to 2 V. According to the previous equations, R2 and R3 are selected to be 11 kΩ and 21 kΩ respectively.