7.3.1 ANY-OUT Programmable Output Voltage

The TPS7A8300 does not require external resistors to set output voltage, which is typical of adjustable low-dropout voltage regulators (LDOs). However, the TPS7A8300 uses pins 5, 6, 7, 9, 10, and 11 to program the regulated output voltage. Each pin is either connected to ground (active) or left open (floating). ANY-OUT programming is set by Equation 1 as the sum of the internal reference voltage (V_REF = 0.8 V) plus the accumulated sum of the respective voltages assigned to each active pin; that is, 50mV (pin 5), 100mV (pin 6), 200mV (pin 7), 400mV (pin 9), 800mV (pin 10), or 1.6V (pin 11). Table 1 summarizes these voltage values associated with each active pin setting for reference. By leaving all program pins open, or floating, the output is thereby programmed to the minimum possible output voltage equal to V_REF.

Equation 1.

Table 2 provides a full list of target output voltages and corresponding pin settings. The voltage setting pins have a binary weight; therefore, the output voltage can be programmed to any value from 0.8 V to 3.95 V in 50-mV steps.

There are several alternative ways to set the output voltage. The program pins can be driven using external general-purpose input/output pins (GPIOs), manually connected to ground using 0-Ω resistors (or left open), or hardwired by the given layout of the printed circuit board (PCB) to set the ANY-OUT voltage.

7.3.2 Adjustable Operation

The TPS7A8300 can be used either with the internal ANY-OUT network or using external resistors. Using the ANY-OUT network allows the TPS7A8300 to be programmed from 0.8 V to 3.95 V. To extend this range of output voltage operation to 5.0 V, external resistors must be used. This configuration is referred to as the adjustable configuration of the TPS7A8300 throughout this document. Regardless whether the internal resistor network or whether external resistors are used, the nominal output voltage of the device is set by two resistors, as shown in Figure 50. Using an internal resistor ensures a 1% matching and minimizes both the number of external components and layout footprint.

Figure 50. Adjustable Operation for Maximum AC Performance

R₁ and R₂ can be calculated for any output voltage range using Equation 2. This resistive network must provide a current equal to or greater than 5 μA for optimum noise performance.

Equation 2.

If greater voltage accuracy is required, take into account the output voltage offset contributions resulting from the feedback pin current (I_FB) and use 0.1% tolerance resistors.

Table 3 shows the resistor combination required to achieve a few of the most common rails using commercially-available, 0.1%-tolerance resistors to maximize nominal voltage accuracy while abiding to the formula shown in Equation 2.

7.3.3 ANY-OUT Operation

Considering the use of the ANY-OUT internal network (where the unit resistance of 1R is equal to 6.05 kΩ) the output voltage is set by grounding the appropriate control pins, as shown in Figure 51. When grounded, all control pins add a specific voltage on top of the internal reference voltage (V_REF = 0.8 V). The output voltage can be equated with Equation 4. Figure 51 and Figure 52 show a 1.2-V and 1-V output voltage, respectively, that provide an example of the circuit usage with and without BIAS voltage. These schematics are described in more detail in the Typical Application section.

Figure 51. ANY-OUT Configuration Circuit
(1.4-V Input, 1.2-V Output, No External BIAS)

Figure 52. ANY-OUT Configuration Circuit
(1.1-V Input, 1.0-V Output, 3-V BIAS Voltage)

7.3.4 2-A LDO with an Internal Charge Pump

The TPS7A8300 can be used either with the internal resistor network provided, or with the external component as a traditional adjustable LDO. Regardless of the implementation, the TPS7A8300 provides excellent regulation to 1% accuracy, excellent dropout voltage, and high output current capability.

If the input voltage is below 1.4 V, an external BIAS voltage must be supplied to maintain the dropout characteristics. The input voltage or the BIAS voltage is fed through to a internal charge pump to power the internal error amplifier providing the regulation.

7.3.4.1 Dropout Voltage (V_DO)

Generally speaking, the dropout voltage often refers to the voltage difference between the input and output voltage (V_DO = V_IN – V_OUT). However, in the , V_DO is defined as the V_IN – V_OUT voltage at the rated current (I_RATED), where the main current pass-FET is fully on in the ohmic region of operation and is characterized by the classic R_DS(ON) of the FET. V_DO indirectly specifies a minimum input voltage above the nominal programmed output voltage at which the output voltage is expected to remain within its accuracy boundary. If the input falls below this V_DO limit (V_IN < V_OUT + V_DO), then the output voltage decreases in order to follow the input voltage.

Dropout voltage is always determined by the R_DS(ON) of the main pass-FET. Therefore, if the LDO operates below the rated current, then the V_DO for that current scales accordingly. The R_DS(ON) for the TPS7A8300 can be calculated using Equation 5:

Equation 5.

7.3.5 Low-Noise, 0.8-V Reference

The TPS7A8300 includes a low-noise reference ensuring minimal noise during operation because the internal reference is normally the dominant term in noise analysis. Further noise reduction can be achieved using the NR/SS pin and by adding an external C_FF between the SNS pin and the FB pin.

7.3.6 Internal Protection Circuitry

7.3.7 Programmable Soft-Start

Soft-start refers to the ramp-up characteristic of the output voltage during LDO turn-on after EN and UVLO exceed the respective threshold voltage. The noise-reduction capacitor (C_NR/SS) serves a dual purpose of both governing output noise reduction and programming the soft-start ramp during turn-on. See the Application and Implementation section on implementing a soft-start.

7.3.8 Power-Good Function

The TPS7A8300 has a power-good function that works by toggling the state of the PG output pin. When the output voltage falls below the PG threshold voltage (V_IT(PG)), the PG pin open-drain output engages (low impedance to GND). When the output voltage exceeds the V_IT(PG) threshold by an amount greater than V_HYS(PG), the PG pin becomes high-impedance. By connecting a pull-up resistor to an external supply, any downstream device can receive PG as a logic signal. Make sure that the external pull-up supply voltage results in a valid logic signal for the receiving device or devices. Use a pull-up resistor from 10 kΩ to 100 kΩ for best results.

When employing the feed-forward capacitor (C_FF), the turn-on time-constant for the LDO is increased and the power-good output time-constant stays the same, resulting in an invalid status of the LDO. To avoid this issue and receive a valid PG output, ensure that the time-constant of both the LDO and the power-good output match. For more details, see application report, Pros and Cons of Using a Feed-Forward Capacitor with a Low Dropout Regulator, SBVA042.

7.3.9 Integrated Resistance Network (ANY-OUT)

An internal resistance network is provided allowing the TPS7A8300 output voltage to be programmed easily between 0.8 V to 3.95 V with a 50-mV step.

7.4.1 Operation with 1.1 V > V_IN > 1.4 V

The TPS7A8300 requires a bias voltage on the BIAS pin ≥ 3.0 V if the high-current input supply voltage is between 1.1 to 1.4 V. The bias voltage pin consumes 2.3 mA, nominally.

7.4.2 Operation with 1.4 V ≥ V_IN > 6.5 V

If the input voltage is equal to, or exceeds 1.4 V, no bias voltage is necessary. The device is automatically selected to be powered from the IN pin in this condition and the BIAS pin can be left floating.

7.4.3 Disabled

If the voltage on the EN pin is less than 0.5 V, the device is disabled and the output is high impedance. The output impedance of the LDO is then set by the gain setting resistors if a path to GND is provided between OUT and GND. Raising EN above 1.1 V (maximum) initiates the startup sequence of the device. In this state, quiescent current does not exceed 2.5 µA.