R16DS0137EU0100 Rev.1.0

Page 16

Apr 13, 2021

RAA210040 Datasheet

When the FS pin is directly tied to VIN, the frequency of operation is fixed at 2MHz. See Table 1 to help with the

selection of switching frequency for typical operation conditions. More detailed information on recommended

switching frequency is provided in the Switching Frequency Selection section.

5.3

Overcurrent Protection (OCP)

The overcurrent protection is implemented by monitoring the CSA output with the OCP comparator, as shown in

Figure 4. The current-sensing circuit has a gain of 200mV/A, from the P-channel MOSFET current to the CSA

output. When the CSA output reaches the threshold, the OCP comparator is tripped and turns off the P-channel

MOSFET immediately. The overcurrent function protects the module from a shorted output by monitoring the

current flowing through the P-channel MOSFET.

With the detection of an overcurrent condition, the P-channel MOSFET is immediately turned off and is not turned

on again until the next switching cycle. With the detection of the initial overcurrent condition, the overcurrent fault

counter is set to 1. During the subsequent cycle, if another overcurrent condition is detected, the OC fault counter

is incremented. If there are 17 sequential OC fault detections, the module shuts down under an overcurrent fault

condition. An overcurrent fault condition results in the module attempting to restart in Hiccup mode within the

delay of eight soft start-up periods. At the end of the eighth soft start-up wait period, the fault counters are reset

and soft start-up is attempted again. If the overcurrent condition goes away during the delay of eight soft start-up

periods, the output resumes back into regulation after the Hiccup mode expires as shown in Figure 34.

5.4

Negative Current Protection

Similar to overcurrent, the negative current protection is realized by monitoring the current across the low-side

N-channel MOSFET, as shown in Figure 4. When the valley point of the inductor current reaches -3A for four

consecutive cycles, both P-channel MOSFET and N-channel MOSFET are turned off. The 100Ω in parallel to the

N-channel MOSFET activates discharging the output into regulation. The control begins to switch when output is

within regulation.

5.5

Power-Good

Power-Good (PG) is the open-drain output of a window comparator that continuously monitors the module output

voltage. PG is actively held low when EN is low and during the module soft start-up period. After the 1ms delay of

the soft start-up period, PG becomes high impedance as long as the output voltage is within the nominal

regulation voltage set by VFB. During an output overvoltage fault condition (output voltage is 33% higher than

nominal value) or an output undervoltage fault condition (output voltage is 15% lower than nominal value), PG is

pulled low. Any fault condition forces PG low until the fault condition is cleared during soft start-up. For logic level

output voltages, connect an external pull-up resistor between PG and VIN. A 100kΩ resistor works well in most

applications.

Figure 34. OCP Response; Output Short-Circuited from No Load to Ground and Released, VOUT = 1.2V

8ms

IIN 2A/Div

VOUT 1V/Div

PG 5V/Div

500µs/Div