Table 7-2. Power Good Pin Logic (continued)

DEVICE STATE

PG LOGIC STATUS

HIGH IMPEDANCE

LOW

Power Supply Removal

√

7.3.8 Noise Reduction and Soft-Start Capacitor (NR/SS)

A capacitor connected to this pin reduces the low frequency noise of the converter and sets the soft-start time.

The larger the capacitor, the lower the noise and the longer the start-up time of the converter. A 470-nF capacitor

is typically connected to this pin for a start-up time of 5 ms, although longer and shorter start-up times can be

used. During soft start with a light load, the device skips switching pulses as needed to not discharge the output

voltage. The device can start into a pre-biased output voltage.

The device achieves low noise by adding an R-C filter to the reference voltage, as shown in Section 7.2. During

start-up, the NR/SS capacitor is charged with a constant current of 75 µA (typ) to 0.8 V. Larger NR/SS capacitors

provide for lower low frequency noise, as shown in Figure 6-28. The maximum NR/SS cap is 3.3 µF for a start-

up time of 35 ms. The minimum start-up time is set internally to 0.7 ms, which occurs when there is a small

NR/SS capacitor or no NR/SS capacitor.

7.3.9 Current Limit and Short Circuit Protection

The device is protected against short circuits and overcurrent. The switch current limit prevents the device from

high inductor current and from drawing excessive current from the input voltage rail. Excessive current can occur

with a shorted/saturated inductor or a heavy load/shorted output circuit condition. If the inductor current reaches

the inductor current. The high-side MOSFET is turned on again only when the low-side current is below the low-

Due to internal propagation delay, the actual current can exceed the static current limit, especially if the input

voltage is high and very small inductances are used. The dynamic current limit is calculated as follows:

(

)

L

peak typ

SWpeak

PD

V

I

I

t

L

§

·

u

¨

¸

©

¹

(1)

where

• L is the inductance

The low-side MOSFET also contains a negative current limit to prevent excessive current from flowing back

through the inductor to the input. If the low-side sinking current limit is exceeded, the low-side MOSFET is turned

off. In this scenario, both MOSFETs are off until the start of the next cycle.

7.3.10 Thermal Shutdown

The device goes into thermal shutdown once the junction temperature exceeds typically 170°C with a 20°C

hysteresis.

7.4 Device Functional Modes

7.4.1 Fixed Frequency Pulse Width Modulation

To minimize output voltage ripple, the device operates in fixed frequency PWM operation down to no load. The

switching frequency of 1 MHz or 2.2 MHz is selected using the S-CONF pin.

TPS62912, TPS62913

SLVSFP4 – AUGUST 2020

www.ti.com

18

Submit Document Feedback

Copyright © 2020 Texas Instruments Incorporated

Product Folder Links: TPS62912 TPS62913