The TPS6513x operates with an input voltage range of 2.7 V to 5.5 V and can generate both a positive and negative output. Both converters work independently of each other. They only share a common clock and a common voltage reference. Both outputs are separately controlled by a fixed-frequency, pulse-width-modulated (PWM) regulator. In general, each converter operates at continuous conduction mode (CCM). At light loads, the negative converter can enter discontinuous conduction mode (DCM). As the load current decreases, the converters can enter a power-save mode if enabled. This works independently at both converters. Output voltages can go up to 15 V at the boost output and down to –15 V at the inverter output.
Both converters operate in a fixed-frequency, PWM control scheme. So, the ON-time of the switches varies depending on input-to-output voltage ratio and the load. During this ON-time, the inductors connected to the converters charge with current. In the remaining time, the time period set by the fixed operating frequency, the inductors discharge into the output capacitors through the rectifier diodes. Usually at greater loads, the inductor currents are continuous. At lighter loads, the boost converter uses an additional internal switch to allow current flowing back to the input. This avoids inductor current becoming discontinuous in the boost converter. So, the boost converter is always controlled in a continuous current mode. At the inverting converter, during light loads, the inductor current can become discontinuous. In this case, the control circuit of the inverting controller output automatically takes care of these changing conditions to always operate with an optimum control setup.
The controller circuits of both converters employ a fixed-frequency, multiple-feedforward controller topology. The circuits monitor input voltage, output voltage, and voltage drop across the switches. Changes in the operating conditions of the converters directly affect the duty cycle and must not take the indirect and slow way through the output voltage control loops. Measurement errors in this feedforward system are corrected by a self-learning control system. An external capacitor damps the output to avoid output-voltage steps due to output changes of this selflearning control system.
The voltage loops, determined by the error amplifiers, must only handle small signal errors. The error amplifiers feature internal compensation. Their inputs are the feedback voltages on the FBP and FBN pins. The device uses a comparison of these voltages with the internal reference voltage to generate an accurate and stable output voltage.
Both converters can be enabled or disabled individually. Applying a logic HIGH signal at the enable pins (ENP for the boost converter, ENN for the inverting converter) enables the corresponding output. After enabling, internal circuitry, necessary to operate the specific converter, then turns on, followed by the Soft-Start.
AApplying a low signal at the enable ENP or ENN pin shuts down the corresponding converter. When both enable pins are low, the device enters shutdown mode, where all internal circuitry turns off. The device now consumes shutdown current flowing into the VIN pin. The output loads of the converters can be disconnected from the input, see Load Disconnect.
The device supports completely disconnecting the load when the converters are disabled. For the inverting converter, the device turns off the internal PMOS switch. If the inverting converter is turned off, no DC current path remains which could discharge the battery or supply.
This is different for the boost converter. The external rectifying diode, together with the boost inductor, form a DC current path which could discharge the battery or supply if any load connects to the output. The device has no internal switch to prevent current from flowing. For this reason, the device offers a PMOS gate control output (BSW) to enable and disable a PMOS switch in this DC current path, ideally directly between the boost inductor and battery. To be able to fully disconnect the battery, the forward direction of the parasitic backgate diode of this switch must point to the battery or supply. The external PMOS switch, which connects to BSW, turns on when the boost converter is enabled and turns off when the boost converter is disabled.
Both converters have implemented soft-start functions. When each converter is enabled, the implemented switch current limit ramps up slowly to its nominal programmed value in about 1 ms. Soft-start is implemented to limit the input current during start-up to avoid high peak currents at the battery which could interfere with other systems connected to the same battery. Without soft-start, the high input peak current could trigger the implemented switch current limit, which can lead to a significant voltage drops across the series resistance of the battery and its connections.
Both converters (boost and inverter) have implemented individual overvoltage protection. If the feedback voltage under normal operation exceeds the nominal value by typically 5%, the corresponding converter shuts down immediately to protect any connected circuitry from possible damage.
An undervoltage lockout (UVLO) prevents the device from starting up and operating if the supply voltage at the VIN pin is lower than the undervoltage lockout threshold. For this case, the device automatically shuts down both converters when the supply voltage at VIN falls below this threshold. Nevertheless, parts of the control circuits remain active, which is different than device shutdown.
The device automatically shuts down both converters if the implemented internal temperature sensor detects a chip temperature above the thermal shutdown temperature. It automatically starts operating again when the chip temperature falls below this thermal shutdown temperature. The built-in hysteresis avoids undefined operation caused by ringing from shutdown and prevents operating at a temperature close to the overtemperature shutdown threshold.
The power-save mode can improve efficiency at light loads. In power-save mode, the converter only operates when the output voltage falls below an device internally set threshold voltage. The converter ramps up the output voltage with one or several operating pulses and goes again into power-save mode once the inductor current becomes discontinuous.
The PSN and PSP logic level selects between power-save mode and continuous-conduction mode. If the specific pins (PSP for the boost converter, PSN for the inverting converter) are HIGH, the power-save mode for the corresponding converter operates at light loads. Similarly, a LOW on the PSP pin or PSN pin disables the power-save mode for the corresponding converter.
The recommended minimum input supply voltage for the TPS6513x device is 2.7 V. Above this voltage, the device achieves the performance described in this data sheet.
With input supply voltages between VUVLO and 2.7 V, the device continues to operate — no functions are disabled — but full performance is not ensure.
The TPS6513x enters an undervoltage lockout condition when the input supply voltage is below the UVLO threshold. In this mode, all device functions are disabled, and the input supply current consumption is minimized. See also the Undervoltage Lockout section.