Datasheet

EN
i
1
i
hys
VIN
+
-
TPS54218
R1
R2
0.6 mA
2.55 mA
VSENSE
V
O
+
-
TPS54218
R1
R2
0.8V
O
0.8 V
R2 = R1
V 0.8 V
æ ö
´
ç ÷
-
è ø
TPS54218
SLVS974B –SEPTEMBER 2009–REVISED JULY 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. It is recommended to
use divider resistors with 1% tolerance or better. Start with a 100 kΩ for the R1 resistor and use the Equation 1
to calculate R2. To improve efficiency at very 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 UNDER-VOLTAGE LOCKOUT
The TPS54218 is disabled when the VIN pin voltage falls below 2.6 V. If an application requires a higher under-
voltage lockout (UVLO), use the EN pin as shown in Figure 24 to adjust the input voltage UVLO by using two
external resistors. It is recommended 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 TPS54218
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 Under Voltage Lock Out
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