Datasheet
Table Of Contents
- FEATURES
- APPLICATIONS
- DESCRIPTION
- ABSOLUTE MAXIMUM RATINGS
- THERMAL INFORMATION
- ELECTRICAL CHARACTERISTICS
- DEVICE INFORMATION
- TYPICAL CHARACTERISTICS
- OVERVIEW
- DETAILED DESCRIPTION
- Fixed Frequency PWM Control
- Slope Compensation Output Current
- Pulse Skip Eco-Mode
- Low Dropout Operation and Bootstrap Voltage (BOOT)
- Error Amplifier
- Voltage Reference
- Adjusting the Output Voltage
- Enable and Adjusting Undervoltage Lockout
- Slow Start/Tracking Pin (SS/TR)
- Overload Recovery Circuit
- Sequencing
- Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
- Overcurrent Protection and Frequency Shift
- Selecting the Switching Frequency
- How to Interface to RT/CLK Pin
- Power Good (PWRGD Pin)
- Overvoltage Transient Protection
- Thermal Shutdown
- Small Signal Model for Loop Response
- Simple Small Signal Model for Peak Current Mode Control
- Small Signal Model for Frequency Compensation
- APPLICATION INFORMATION
- Design Guide — Step-By-Step Design Procedure
- Selecting the Switching Frequency
- Output Inductor Selection (LO)
- Output Capacitor
- Catch Diode
- Input Capacitor
- Slow Start Capacitor
- Bootstrap Capacitor Selection
- Under Voltage Lock Out Set Point
- Output Voltage and Feedback Resistors Selection
- Compensation
- Discontinuous Mode and Eco Mode Boundary
- APPLICATION CURVES
- Power Dissipation Estimate
- Layout
- Revision History
Tss(ms) Iss( A)
Css(nF) =
Vref (V) 0.8
m´
´
EN
SS/TR
V
SENSE
VOUT
TPS54060
www.ti.com
SLVS919A –JANUARY 2009–REVISED JULY 2010
DETAILED DESCRIPTION (continued)
Slow Start/Tracking Pin (SS/TR)
The TPS54060 effectively uses the lower voltage of the internal voltage reference or the SS/TR pin voltage as
the power-supply's reference voltage and regulates the output accordingly. A capacitor on the SS/TR pin to
ground implements a slow start time. The TPS54060 has an internal pull-up current source of 2mA that charges
the external slow start capacitor. The calculations for the slow start time (10% to 90%) are shown in Equation 6.
The voltage reference (V
REF
) is 0.8 V and the slow start current (I
SS
) is 2mA. The slow start capacitor should
remain lower than 0.47mF and greater than 0.47nF.
(6)
At power up, the TPS54060 will not start switching until the slow start pin is discharged to less than 40 mV to
ensure a proper power up, see Figure 30.
Also, during normal operation, the TPS54060 will stop switching and the SS/TR must be discharged to 40 mV,
when the VIN UVLO is exceeded, EN pin pulled below 1.25V, or a thermal shutdown event occurs.
The VSENSE voltage will follow the SS/TR pin voltage with a 45mV offset up to 85% of the internal voltage
reference. When the SS/TR voltage is greater than 85% on the internal reference voltage the offset increases as
the effective system reference transitions from the SS/TR voltage to the internal voltage reference (see
Figure 23). The SS/TR voltage will ramp linearly until clamped at 1.7V.
Figure 30. Operation of SS/TR Pin when Starting
Overload Recovery Circuit
The TPS54060 has an overload recovery (OLR) circuit. The OLR circuit will slow start the output from the
overload voltage to the nominal regulation voltage once the fault condition is removed. The OLR circuit will
discharge the SS/TR pin to a voltage slightly greater than the VSENSE pin voltage using an internal pull down of
100mA when the error amplifier is changed to a high voltage from a fault condition. When the fault condition is
removed, the output will slow start from the fault voltage to nominal output voltage.
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