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MIC21LV32 Datasheet(PDF) 25 Page - Microchip Technology |
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MIC21LV32 Datasheet(HTML) 25 Page - Microchip Technology |
25 / 50 page ![]() 2021 Microchip Technology Inc. DS20006513A-page 25 MIC21LV32 For linearization and fitting the temperature coefficient of the bottom MOSFET RDSON, a resistance network from the ILIM pin to AGND, used with an NTC resistor, is shown in Figure 4-9. FIGURE 4-9: Resistance Network Used with RNTC Resistor for Linearization and Fitting the Temperature Coefficient of RDSON. In case a temperature-independent resistor sensing is used, a simple temperature constant standard resistance is used on the ILIM pin. 4.5.3 NEGATIVE CURRENT LIMIT The MIC21LV32 supports a cycle-by-cycle negative current limit. The absolute value of the negative current-limiting threshold is 50% of the programmed current limit. If the negative low-side MOSFET current is going to trigger a negative current limit, the low-side MOSFET will be turned off and allow current through the high-side MOSFET body diode. During this time, the output voltage tends to rise, because this protection limits the current to discharge the output capacitor. In order to prevent a huge reverse current over the short limit value, the low-side FET turns on after 500 ns, maintaining negative current at programmed level. 4.5.4 PRECISION ENABLE (EN) The precision Enable (EN) input is used to control the regulator. The precision feature allows the simple sequencing of multiple power supplies with a resistor divider from another supply. Connecting this pin to ground, or to a voltage lower than 1.2V (typ.), will turn off the regulator. In this state, the current drain from the input supply is 25 µA (typical) at a 12V input voltage. The EN input has an internal pull-up of about 6 µA. Therefore, this pin can be left floating or pulled to a volt- age greater than 1.2V (typical) to turn the regulator on. The hysteresis on this input is about 65 mV (typical) below the 1.2V (typical) threshold. When driving the enable input, the voltage must never exceed the abso- lute maximum specification for this pin. Although an internal pull-up is provided on the EN pin, it is a good practice to pull the input high when this feature is not used, especially in noisy environments. This can be done easily by connecting a high-value resistor (1 MΩ) between the VIN and EN pins. The MIC21LV32 device also incorporates an internal input Undervoltage Lock- out (UVLO) feature. This prevents the regulator from turning on when the input voltage is not high enough to properly bias the internal circuitry. The rising threshold is 4.3V (typ.) while the falling threshold is 3.9V (typ). In some cases, these thresholds may be too low to provide good system performance. The solution is to use the EN input as an external programmable input UVLO to disable the part when the input voltage falls below a target lower threshold. This is often used to prevent excessive battery discharge or early turn-on during start-up. This method is also recommended to prevent abnormal device operation in applications where the input voltage falls below the minimum of 4.5V. Figure 4-10 shows the connections to implement this method of UVLO. Equation 4-17 and Equation 4-18 can be used to determine the correct resistor values. EQUATION 4-17: EQUATION 4-18: Due to the 6 µA pull-up, the current in the divider should be much higher than this. A value of 20 kΩ for RBOT is a good first choice. Where: RTOP = Top Resistor of the VIN Voltage Resistor Divider RBOT = Bottom Resistor of the VIN Voltage Resistor Divider VOFF = Target VIN Voltage Below which the Regulator Turns Off VENTH = Device Enable Upper Threshold Voltage VENHYS = Enable Threshold Hysteresis RTOP = RBOT × VOFF VENTH – VENHYS – 1 Where: VOFF = Input Voltage where the Regulator Shuts Off VON = Input Voltage where the Regulator Turns On VENHYST = Enable Threshold Hysteresis VENTH = Enable Upper Threshold Voltage VON = VOFF × VENTH VENTH – VENHYS |
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