TPS43060
TPS43061
SLVSBP4A –DECEMBER 2012–REVISED DECEMBER 2012
www.ti.com
100
95
90
85
80
75
70
50 150 250 350 450 550 650 750 850 950 1050
C019
Frequency (kHz)
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 (CSS) 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.
1.22V
t = C
ss
ss
5mA
(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.
14
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