The TPS7H401x can be configured as an inverting
buck-boost to create a negative output voltage as shown in Figure 10-4.
Additional considerations for designing an
inverting buck-boost are described in the application note, Working With Inverting
Buck-Boost Converters. While many details and equations are provided
within the application note, a few considerations for the TPS7H401x are as follows:
- Maintain that the recommended
maximum input voltage of 14V is followed. This means VIN + |VOUT| ≤ 14V. For
example, an inverting buck-boost configured from 5V to –5V is acceptable
(10V differential) but 12V to –12V is not acceptable (24V
differential).
- Be sure the current limit
supports the application . The average inductor current for an inverting
buck-boost is greater than the load current. This can result in higher peak
currents than expected when compared to a buck converter. Additionally, this
means that the average inductor current must be kept lower than the
TPS7H4012 recommended maximum of 6A and TPS7H4013 maximum of 3A.
- CIO in the Figure 10-4 is the standard input capacitor that is utilized in a buck converter.
CIN is an input capacitor with respect to system ground which
provides a low impedance path at the regulator input.
- Be sure that device logic
input pins such as EN never exceed the recommended maximum rating of 7V. For
example, if EN is driven to 5V from an external source and the inverting
buck-boost is configured for a –5V output, this applies 10V to EN (with
respect to the device GND pin) which exceeds the rating. Take care with
selecting the input voltage signals to avoid this condition. Alternatively,
logic shift the signals so the signals are referenced with respect to -VOUT
(which is the device GND pin).