7.2.1 Design Requirements

Table 7-2 lists the design requirements.

Table 7-2. Design Parameters

PARAMETER

DESIGN REQUIREMENTS

Input voltage

3V – 4V (lithium ion battery)

Output voltage

2.8V

DC output current

10mA

Peak output current

75mA

Maximum ambient temperature

65°C

7.2.2 Detailed Design Procedure

7.2.2.1 Capacitor Recommendations

Low equivalent series resistance (ESR) capacitors must be used for the input, output, noise reduction, and

bypass capacitors. Ceramic capacitors with X7R and X5R dielectrics are preferred. These dielectrics offer more

stable characteristics. Ceramic X7R capacitors offer improved over-temperature performance, while ceramic

X5R capacitors are more cost-effective and are available in higher values.

7.2.2.2 Input and Output Capacitor Requirements

A 0.1μF or larger ceramic input bypass capacitor, connected between IN and GND and located close to the

legacy chip of TPS792xx, is required for stability and improves transient response, noise rejection, and ripple

rejection. A 1μF or larger ceramic input bypass capacitor, connected between IN and GND and located close to

the new chip of TPS792xx, is required for stability and improves transient response, noise rejection, and ripple

rejection. A higher-value input capacitor can be necessary if large, fast-rise-time load transients are anticipated

or the device is located several inches from the power source.

Like most low-dropout regulators, the TPS792xx requires an output capacitor connected between OUT and GND

to stabilize the internal control loop. The minimum recommended capacitance is 2.2μF. Any 2.2μF or larger

ceramic capacitor is suitable, provided the capacitance does not vary significantly over temperature. If load

current is not expected to exceed 100 mA, a 1.0μF ceramic capacitor can be used. If a feed-forward capacitor

is not used (such as in a unity-gain configuration) or if an output voltage less than 1.8V is chosen, then the

minimum recommended output capacitor is 4.7μF instead of 2.2μF. The table below lists the recommended

output capacitor sizes for several common configurations.

Table 7-3. Output Capacitor Sizing

Condition

COUT (µF)

VOUT < 1.8V or CFF = 0nF

4.7

VOUT > 1.8V, IOUT > 100mA

2.2

VOUT > 1.8V, IOUT < 100mA

1

7.2.2.3 Noise Reduction and Feed-Forward Capacitor Requirements

The internal voltage reference is a key source of noise in an LDO regulator. The legacy chip of TPS792xx has

an NR pin which is connected to the voltage reference through a 250kΩ internal resistor. The 250kΩ internal

resistor, in conjunction with an external bypass capacitor connected to the NR pin, creates a low-pass filter to

reduce the voltage reference noise and, therefore, the noise at the regulator output. In order for the regulator to

operate properly, the current flow out of the NR pin must be at a minimum, because any leakage current creates

an IR drop across the internal resistor, thus creating an output error. Therefore, the bypass capacitor must have

minimal leakage current. The bypass capacitor must be no more than 0.1μF to verify that the capacitor is fully

charged during the quick-start time provided by the internal switch in the Functional Block Diagrams.

A feed-forward capacitor is recommended when using the adjustable version, to improve the stability of the

device. If R2 = 30.1kΩ, set C1 to 15pF for optimal performance. For voltages less than 1.8V, the value of this

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TPS792

SLVS337E – MARCH 2001 – REVISED JANUARY 2025

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