Datasheet

Vout 0.8V
R1 = R2
0.8 V
-
æ ö
´
ç ÷
è ø
EN
VIN
+
-
TPS54060
R1
R2
Ihys
I1
0.9 Am
1.25V
2.9 Am
START STOP
HYS
V V
R1
I
-
=
ENA
START ENA
1
V
R2
V V
I
R1
=
-
+
TPS54060
www.ti.com SLVS919A –JANUARY 2009–REVISED JULY 2010
DETAILED DESCRIPTION (continued)
Adjusting the Output Voltage
The output voltage is set with a resistor divider from the output node to the VSENSE pin. It is recommended to
use 1% tolerance or better divider resistors. Start with a 10 kΩ for the R2 resistor and use the Equation 1 to
calculate R1. To improve efficiency at light loads consider using larger value resistors. If the values are too high
the regulator will be more susceptible to noise and voltage errors from the VSENSE input current will be
noticeable
(1)
Enable and Adjusting Undervoltage Lockout
The TPS54060 is disabled when the VIN pin voltage falls below 2.5 V. If an application requires a higher
undervoltage lockout (UVLO), use the EN pin as shown in Figure 28 to adjust the input voltage UVLO by using
the two external resistors. Though it is not necessary to use the UVLO adjust registers, for operation it is highly
recommended to provide consistent power up behavior. The EN pin has an internal pull-up current source, I1, of
0.9mA that provides the default condition of the TPS54060 operating when the EN pin floats. Once the EN pin
voltage exceeds 1.25V, an additional 2.9mA of hysteresis, Ihys, is added. This additional current facilitates input
voltage hysteresis. Use Equation 2 to set the external hysteresis for the input voltage. Use Equation 3 to set the
input start voltage.
Figure 28. Adjustable Undervoltage Lockout (UVLO)
(2)
(3)
Another technique to add input voltage hysteresis is shown in Figure 29. This method may be used, if the
resistance values are high from the previous method and a wider voltage hysteresis is needed. The resistor R3
sources additional hysteresis current into the EN pin.
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