Datasheet

START STOP
OUT
HYS
V V
R1
V
I
R3
-
=
+
EN
Ihys
VIN
+
-
TPS57040-Q1
R1
R2
VOUT
R3
I1
0.9 Am
2.9 Am
1.25 V
ENA
START ENA
1
V
R2
V V
I
R1
=
-
+
START STOP
HYS
V V
R1
I
-
=
EN
VIN
+
-
TPS57040-Q1
R1
R2
Ihys
I1
0.9 Am
1.25 V
2.9 Am
TPS57040-Q1
www.ti.com SLVSAP4C –DECEMBER 2010–REVISED OCTOBER 2012
DETAILED DESCRIPTION (continued)
Enable and Adjusting Undervoltage Lockout
The TPS57040-Q1 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 resistors, for operation it is highly
recommended to provide consistent power up behavior. The EN pin has an internal pull-up current source, I1, of
0.9 μA that provides the default condition of the TPS57040-Q1 operating when the EN pin floats. Once the EN
pin voltage exceeds 1.25 V, an additional 2.9 μA of hysteresis, I
HYS
, 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.
Figure 29. Adding Additional Hysteresis
(4)
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