8.2.1.2.1 Supply and Enable Voltages

To ensure proper operation, V_EN and V_IN must be within a specified range. An acceptable range of input voltages is calculated by Equation 2:

The EN pin uses an internal pullup current source (I_PULLUP ≊ 2 µA) that may be left floating or triggered by an external source. If the device is not enabled by an external source, it may be connected to V_IN. An acceptable range of enable voltages is given by Figure 4. See Electrical Characteristics LM4132-1.8 (VOUT = 1.8 V) and Figure 3 for more detail. The device does not operate correctly for V_EN > V_IN.

8.2.1.2.2 Component Selection

A small ceramic (X5R or X7R) capacitor on the input must be used to ensure stable operation. The value of C_IN must be sized according to the output capacitor value. The value of C_IN must satisfy the relationship C_IN ≥ C_OUT. When no output capacitor is used, C_IN must have a minimum value of 0.1 µF. Noise on the power-supply input may affect the output noise. Larger input capacitor values (typically 4.7 µF to 22 µF) may help reduce noise on the output and significantly reduce overshoot during start-up. Use of an additional optional bypass capacitor from the input and ground may help further reduce noise on the output. With an input capacitor, the LM4132 drives any combination of resistance and capacitance up to V_REF / 20 mA and 10 µF, respectively.

The LM4132 is designed to operate with or without an output capacitor and is stable with capacitive loads up to 10 µF. Connecting a capacitor from the output and ground significantly improves the load transient response when switching from a light load to a heavy load. The output capacitor must not be made arbitrarily large because capacitor selection affects the turnon time as well as line and load transients.

While a variety of capacitor chemistry types may be used, it is typically advisable to use low equivalent series resistance (ESR) ceramic capacitors. Such capacitors provide a low impedance to high frequency signals, effectively bypassing them to ground. Bypass capacitors must be mounted close to the device. Mounting bypass capacitors close to the device helps reduce the parasitic trace components thereby improving performance.

8.2.1.2.3 Temperature Coefficient

Temperature drift is defined as the maximum deviation in output voltage over the operating temperature range. This deviation over temperature may be shown in Figure 48:

Figure 48. V_REF vs Temperature Profile

Temperature coefficient may be expressed analytically as Equation 3:

Equation 3.

where

• T_D = Temperature drift
• V_REF = Nominal preset output voltage
• V_{REF_MIN} = Minimum output voltage over operating temperature range
• V_{REF_MAX} = Maximum output voltage over operating temperature range
• ΔT = Operating temperature range
• The LM4132 features a low temperature drift of 10 ppm (maximum) to 30 ppm (maximum), depending on the grade.

8.2.1.2.4 Long-Term Stability

Long-term stability refers to the fluctuation in output voltage over a long period of time (1000 hours). The LM4132 features a typical long-term stability of 50 ppm over 1000 hours. The measurements are made using 5 units of each voltage option, at a nominal input voltage (5 V), with no load, at room temperature.

8.2.1.2.5 Expression of Electrical Characteristics

Electrical characteristics are typically expressed in mV, ppm, or a percentage of the nominal value. Depending on the application, one expression may be more useful than the other. To convert one quantity to the other one may apply the following:

ppm to mV error in output voltage:

Equation 4.

where

• V_REF is in volts (V)
• V_ERROR is in millivolts (mV)

Bit error (1 bit) to voltage error (mV):

Equation 5.

where

• V_REF is in volts (V)
• V_ERROR is in millivolts (mV)
• n is the number of bits

mV to ppm error in output voltage:

Equation 6.

where

• V_REF is in volts (V)
• V_ERROR is in millivolts (mV)

Voltage error (mV) to percentage error (percent):

Equation 7.

where

• V_REF is in volts (V)
• V_ERROR is in millivolts (mV)