Datasheet

1.22

ss ss

t C

100

50 150 250 350 450 550 650 750 850 950 1050

Max Duty Cycle (%)

Frequency (kHz)

C019

TPS43060

TPS43061

SLVSBP4C –DECEMBER 2012–REVISED SEPTEMBER 2013

www.ti.com

Figure 19. Maximum Duty Cycle vs Frequency

SOFT-START

The TPS43060 and TPS43061 have a built-in soft-start circuit which significantly reduces the start-up current

spike and output voltage overshoot. When the IC is enabled, an internal bias current source (5 µA typical)

charges the capacitor (C

) on the SS pin. When the SS pin voltage is less than the internal 1.22 V reference,

the device regulates the FB pin voltage to the SS pin voltage rather than the internal 1.22 V reference voltage.

Once the SS pin voltage exceeds the reference voltage the device regulates the FB pin voltage to 1.22V. The

soft-start time of the output voltage can be calculated using Equation 9.

(9)

POWER GOOD

The TPS43060 and TPS43061 PGOOD pin indicates when the output voltage is within pre-determined limits of

the desired regulated output voltage by monitoring the FB pin voltage. The PGOOD pin is driven by the open-

drain signal of an internal MOSFET. When the output voltage of the power converter is not within ±10% of the

output voltage set point, the PGOOD MOSFET turns on and pulls the PGOOD pin low. Otherwise, the PGOOD

MOSFET stays off and the PGOOD pin can be pulled up by an external resistor to a voltage supply up to 8V.

OVERVOLTAGE PROTECTION

The TPS43060 and TPS43061 integrate an overvoltage protection (OVP) circuit that turns off the low side

MOSFET when the output voltage reaches the OVP threshold which is internally fixed to 107% of the output

voltage set point. The low side MOSFET resumes normal PWM control when the output voltage drops below

105% of the output voltage set point. The OVP circuit protects the power MOSFETs and minimizes the output

voltage overshoot during transients or fault conditions.

OVERCURRENT PROTECTION AND CURRENT SENSE RESISTOR SELECTION

The TPS43060 and TPS43061 provide cycle-by-cycle current limit protection that turns off the low side MOSFET

when the inductor current reaches the current limit threshold. The cycle-by-cycle current limit circuitry is reset at

the beginning of the next switching cycle. During an overcurrent event, the output voltage begins to droop as a

function of the load on the output.

A slope compensation ramp is added to the current sense ramp to prevent sub-harmonic oscillations at high duty

cycle. The slope compensation reduces the overcurrent limit threshold (maximum current sense threshold) with

increasing duty cycle as detailed in Figure 20.

Product Folder Links: TPS43060 TPS43061