Datasheet

-
× -
´
START STOP
6
0.944 V V
R1 =
2.59 10
EN
i
1
i
hys
VIN
+
-
TPS54318
R1
R2
0.6 mA
2.55 mA
VSENSE
V
O
+
-
TPS54318
R1
R2
0.8V
O
0.8 V
R2 = R1
V 0.8 V
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TPS54318
SLVS975A –SEPTEMBER 2009–REVISED SEPTEMBER 2013 www.ti.com
VOLTAGE REFERENCE
The voltage reference system produces a precise ±1% voltage reference overtemperature by scaling the output
of a temperature stable bandgap circuit. The bandgap and scaling circuits produce 0.8 V at the non-inverting
input of the error amplifier.
ADJUSTING THE OUTPUT VOLTAGE
The output voltage is set with a resistor divider from the output node to the VSENSE pin. TI recommends to use
divider resistors with 1% tolerance or better. Start with a 100 kΩ for the R1 resistor and use Equation 1 to
calculate R2. To improve efficiency at light loads consider using larger value resistors. If the values are too high
the regulator is more susceptible to noise, and voltage errors from the VSENSE input current are noticeable.
(1)
Figure 23. Voltage Divider Circuit
ENABLE AND ADJUSTING UNDERVOLTAGE LOCKOUT
The TPS54318 is disabled when the VIN pin voltage falls below 2.6 V. If an application requires a higher
undervoltage lockout (UVLO), use the EN pin as shown in Figure 24 to adjust the input voltage UVLO by using
two external resistors. TI recommends to use the enable resistors to set the UVLO falling threshold (V
STOP
)
above 2.7 V. The rising threshold (V
START
) should be set to provide enough hysteresis to allow for any input
supply variations. The EN pin has an internal pull-up current source that provides the default condition of the
TPS54318 operating when the EN pin floats. Once the EN pin voltage exceeds 1.25 V, an additional 2.55 μA of
hysteresis is added. When the EN pin is pulled below 1.18 V, the 2.55 μA is removed. This additional current
facilitates input voltage hysteresis.
Figure 24. Adjustable Undervoltage Lockout
(2)
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