Datasheet

VSENSE
V
O
+
–
TPS54478
R1
R2
0.6 V
EN
i
p
i
hys
VIN
+
–
TPS54478
R1
R2
0.64 mA
2.76 mA
Vena
1
æ ö
-
ç ÷
è ø
æ ö
- +
ç ÷
è ø
ENFALLING
START STOP
ENRISING
ENFALLING
p h
ENRISING
V
V V
V
R1 =
V
I I
V
( )
´
- + +
ENFALLING
STOP ENFALLING p h
R1 V
R2 =
V V R1 I I
TPS54478
SLVSAS2 – JUNE 2011 www.ti.com
Figure 21. Voltage Divider Circuit
ENABLE AND ADJUSTING UNDER-VOLTAGE LOCKOUT
The TPS54478 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 22 to adjust the input voltage UVLO by using
two external resistors. It is recommended to use the EN resistors to set the UVLO falling threshold (V
STOP
) above
2.6V. 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 TPS54478
operating when the EN pin floats. Once the EN pin voltage exceeds 1.30 V, an additional 2.76 μA of hysteresis is
added. When the EN pin is pulled below 1.21 V, the 2.76 μA is removed. This additional current facilitates input
voltage hysteresis.
Figure 22. Adjustable Under Voltage Lock Out
(2)
vertical spacer
(3)
Where I
h
= 2.76uA, I
p
= 0.64uA, V
ENRISING
= 1.30V, V
ENFALLING
= 1.21V
12 Copyright © 2011, Texas Instruments Incorporated