9.3.1 Controller Circuit

The device is based on a current-mode control topology using a constant frequency pulse-width modulator to regulate the output voltage. The controller limits the current through the power switch on a pulse by pulse basis. The current-sensing circuit is integrated in the device, therefore, no additional components are required. Due to the nature of the boost converter topology used here, the peak switch current is the same as the peak inductor current, which will be limited by the integrated current limiting circuits under normal operating conditions.

The control loop must be externally compensated with an R-C-C network connected to the COMP-pin.

9.3.2 Synchronous Rectifier

The device integrates an N-channel and a P-channel MOSFET transistor to realize a synchronous rectifier. There is no additional Schottky diode required. Because the device uses a integrated low r_DS(on) PMOS switch for rectification, the power conversion efficiency reaches 95%.

A special circuit is applied to disconnect the load from the input during shutdown of the converter. In conventional synchronous rectifier circuits, the backgate diode of the high-side PMOS is forward biased in shutdown and allows current flowing from the battery to the output. This device, however, uses a special circuit to disconnect the backgate diode of the high-side PMOS and so, disconnects the output circuitry from the source when the regulator is not enabled (EN = low).

The benefit of this feature for the system design engineer, is that the battery is not depleted during shutdown of the converter. So, no additional effort has to be made by the system designer to ensure disconnection of the battery from the output of the converter. Therefore, design performance will be increased without additional costs and board space.

9.3.3 Power-Save Mode

The TPS61010 is designed for high efficiency over a wide output current range. Even at light loads, the efficiency stays high because the switching losses of the converter are minimized by effectively reducing the switching frequency. The controller enters a powersave-mode if certain conditions are met. In this mode, the controller only switches on the transistor if the output voltage trips below a set threshold voltage. It ramps up the output voltage with one or several pulses, and goes again into powersave-mode once the output voltage exceeds a set threshold voltage.

9.3.4 Device Enable

The device is shut down when EN is set to GND. In this mode, the regulator stops switching, all internal control circuitry including the low-battery comparator, is switched off, and the load is disconnected from the input (as described above in the synchronous rectifier section). This also means that the output voltage may drop below the input voltage during shutdown.

The device is put into operation when EN is set high. During start-up of the converter, the duty cycle is limited in order to avoid high peak currents drawn from the battery. The limit is set internally by the current limit circuit and is proportional to the voltage on the COMP-pin.

9.3.5 Undervoltage Lockout (UVLO)

The UVLO function prevents the device from starting up if the supply voltage on VBAT is lower than approximately 0.7 V. This UVLO function is implemented in order to prevent the malfunctioning of the converter. When in operation and the battery is being discharged, the device will automatically enter the shutdown mode if the voltage on VBAT drops below approximately 0.7 V.

9.3.6 Autodischarge

The autodischarge function is useful for applications where the supply voltage of a μC, μP, or memory has to be removed during shutdown in order to ensure a defined state of the system.

The autodischarge function is enabled when the ADEN is set high, and is disabled when the ADEN is set to GND. When the autodischarge function is enabled, the output capacitor will be discharged after the device is shut down by setting EN to GND. The capacitors connected to the output are discharged by an integrated switch of 300 Ω, hence the discharge time depends on the total output capacitance. The residual voltage on VOUT is less than 0.4 V after autodischarge.

9.3.7 Low-Battery Detector Circuit (LBI and LBO)

The low-battery detector circuit is typically used to supervise the battery voltage and to generate an error flag when the battery voltage drops below a user-set threshold voltage. The function is active only when the device is enabled. When the device is disabled, the LBO-pin is high impedance. The LBO-pin goes active low when the voltage on the LBI-pin decreases below the set threshold voltage of 500 mV ±15 mV, which is equal to the internal reference voltage. The battery voltage, at which the detection circuit switches, can be programmed with a resistive divider connected to the LBI-pin. The resistive divider scales down the battery voltage to a voltage level of 500 mV, which is then compared to the LBI threshold voltage. The LBI-pin has a built-in hysteresis of 10 mV. See the application section for more details about the programming of the LBI-threshold.

If the low-battery detection circuit is not used, the LBI-pin should be connected to GND (or to VBAT) and the LBO-pin can be left unconnected. Do not let the LBI-pin float.

9.3.8 Antiringing Switch

The device integrates a circuit that removes the ringing that typically appears on the SW-node when the converter enters the discontinuous current mode. In this case, the current through the inductor ramps to zero and the integrated PMOS switch turns off to prevent a reverse current from the output capacitors back to the battery. Due to remaining energy that is stored in parasitic components of the semiconductors and the inductor, a ringing on the SW pin is induced. The integrated antiringing switch clamps this voltage internally to V_BAT and therefore, dampens this ringing.

9.3.9 Adjustable Output Voltage

The devices with fixed output voltages are trimmed to operate with an output voltage accuracy of ±3%.

The accuracy of the adjustable version is determined by the accuracy of the internal voltage reference, the controller topology, and the accuracy of the external resistor. The reference voltage has an accuracy of ±4% over line, load, and temperature. The controller switches between fixed frequency and pulse-skip mode, depending on load current. This adds an offset to the output voltage that is equivalent to 1% of V_O. The tolerance of the resistors in the feedback divider determine the total system accuracy.

Table 1. TPS6101x Operation Modes