SLVSDA7E February 2017 – August 2019 TPS61178
TPS61178x operates at the peak current-mode pulse-width-modulation (PWM). At the beginning of each switching cycle, the low-side FET switch turns on, and the inductor current ramps up to a peak current that is determined by the output of the internal error amplifier. The PWM controller turns off the low-side FET when the peak inductor current reaches a threshold level set by the error amplifier output. After the low-side FET turns off, the high-side synchronous FET is turned on after a short dead time until the beginning of the next oscillator clock cycle or until the inductor current reaches the reverse current sense threshold.
During the portion of the switching cycle when the low-side FET is on, the input voltage is applied across the inductor and stores the energy as the inductor current ramps up. Meanwhile only the output capacitor supplies the load current. When it turns off the low-side FET, the inductor transfers the stored energy via the high-side synchronous FET to replenish the output capacitor and also supply the load current. This operation repeats every switching cycle.
The device features the internal slope compensation to avoid sub-harmonic oscillation that is intrinsic to peak-current mode control at duty cycle larger than 50%. The internal slope compensation may not be adequate to maintain stability for a very low inductance in application.
At the light load condition, the TPS61178x implements two options: Auto PFM mode (TPS61178) and Forced PWM mode (TPS611781) to meet different application requirements.