ZHCS026C December 2010 – February 2016 TPS57060-Q1
PRODUCTION DATA.
The TPS57060-Q1 device implements current mode control which uses the COMP pin voltage to turn off the high-side MOSFET on a cycle-by-cycle basis. Each cycle the switch current and COMP pin voltage are compared, when the peak switch current intersects the COMP voltage, the high side switch is turned off. During overcurrent conditions that pull the output voltage low, the error amplifier responds by driving the COMP pin high, increasing the switch current. The error amplifier output is clamped internally, which functions as a switch current limit.
To increase the maximum operating switching frequency at high input voltages the TPS57060-Q1 device implements a frequency shift. The switching frequency is divided by 8, 4, 2, and 1 as the voltage ramps from 0 to 0.8 vV on VSENSE pin.
The device implements a digital frequency shift to enable synchronizing to an external clock during normal startup and fault conditions. Because the device can only divide the switching frequency by 8, the device operates within a maximum input voltage limit that still allows for frequency shift protection.
During short-circuit events (particularly with high input voltage applications), the control loop has a finite minimum controllable on time and the output has a low voltage. During the switch on time, the inductor current ramps to the peak current limit because of the high input voltage and minimum on time. During the switch off time, the inductor would normally not have enough off time and output voltage for the inductor to ramp down by the ramp up amount. The frequency shift effectively increases the off time allowing the current to ramp down.