7.2.1 Design Requirements

For this design example, use the parameters listed in Table 7-1 as the input parameters.

Table 7-1. Design Parameters

PARAMETER

DESIGN REQUIREMENT

Input voltage

12V

Output voltage

3.3V

Output current

100mA

7.2.2 Detailed Design Procedure

For this design example, the 3.3V, fixed-version LM111733QxxxRQ1 is selected and is powered by a standard

12V input supply. The dropout voltage (VDO) is kept within the LM1117-Q1 dropout voltage specification for the

3.3V output voltage option to keep the device in regulation under all load and temperature conditions for this

design. A 1.0µF output capacitor is recommended for excellent load transient response. The input capacitor is

optional and is used to reduce the input impedance of the circuit and improve the transient response.

As with any regulator, increasing the size of the output capacitor reduces overshoot and undershoot magnitude.

7.2.3 Application Curves

at operating temperature TJ = 25°C, VIN = VOUT(NOM) + 1.5V or 2.5V (whichever is greater), IOUT = 10mA, CIN =

1.0µF, and COUT = 1.0µF (unless otherwise noted).

Time (ms)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

-1

-1.75

0

-1.5

1

-1.25

2

-1

3

-0.75

4

-0.5

5

-0.25

6

0

7

0.25

8

0.5

9

0.75

VIN

IIN

VOUT

IOUT = 0.1A, COUT = 22µF

Figure 7-3. Start-up and Inrush Current With 22µF

at COUT

VIN = 5V, VOUT = 3.3V, ramp rate = 0.4A/µs

Figure 7-4. IOUT Transient From 0mA to 100mA

VIN = 5V, VOUT = 3.3V, ramp rate = 0.5A/µs

Figure 7-5. IOUT Transient From 1mA to 1A

VIN = 5V, VOUT = 3.3V, ramp rate = 0.8A/µs

Figure 7-6. IOUT Transient From 250mA to 850mA

LM1117-Q1

SBVS468 – DECEMBER 2024

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