Datasheet

( )
REF
(TOP)
XVLO
REF
XV_L
V
R = R
V
´
– V
( ) ( )
UV_L
–5
OV_L
UV_L
1.4
R3
V 1.4 V 10 R1
´ ´
=
– ´ + ´
R1
V
( ) ( )
UV_L
–5
-1.4
UV_L
OV_L
1.4 R1 V
R2 = 1
–
V V 10 R1
é ù
´
´
ê ú
+ ´
ë û
TPS2350
www.ti.com SLUS574D –JULY 2003–REVISED OCTOBER 2013
APPLICATION INFORMATION
For example, assume the typical application design targets have been set to undervoltage turn-on at 33 V (input
supply rising), turn-off at 31 V (input voltage falling), and overvoltage shutdown at 72 V. Then Equation 9 yields
R1 = 200 kΩ for the 2-V hysteresis. Once the value of R1 is selected, it is used to calculate resistors R2 and R3.
(10)
(11)
where
• V
UV_L
is the UVLO threshold when the input supply is low; i.e., less than V
UV
, and
• V
OV_L
is the OVLO threshold when the input supply is low; i.e., less than V
OV
Again referring to the Figure 17a schematic, Equation 10 and Equation 11 produce R2 = 4.909 k Ω (4.99 kΩ
selected) and R3 = 3.951 kΩ (3.92 kΩ selected), as shown. For the selected values, the expected nominal
supply thresholds are V
UV_L
= 32.8 V, V
UV_H
= 30.8 V, and V
OV_L
= 72.6 V. The hysteresis of the overvoltage
threshold, as seen at the supply inputs, is given by the quantity (10 µA) × (R1 + R2). For the majority of
applications, this value is very nearly the same as the UV hysteresis, since typically R1 >> R2.
If more independent control is needed for the OVLO hysteresis, there are several options. One option is to use
separate dividers for both the UV and OV pins, as shown in Figure 16b. In this case, once R1 and R8 have been
selected for the required hysteresis per Equation 9, and values for the bottom resistors in the divider (R2 and R9
in Figure 16b) can be calculated using Equation 12.
(12)
where
• R
XVLO
is R2 or R9
• R
(TOP)
is R1 or R8 as appropriate for the threshold being set
• V
XV_L
is the under (V
UV_L
) or overvoltage (V
OV_L
) threshold at the supply input, and
• V
REF
is either V
THUV
or V
THOV
from the specification table, as required for the resistor being calculated.
Reverse Voltage Protection
In some applications, it may be necessary to protect the TPS2350 against reverse polarity supply connections or
input transients. If the potential at either the –VINA or –VINB pin rises above that of the RTN pin, device damage
may result. If the application environment is such that these conditions are anticipated, a small-signal diode
should be inserted between the supply return bus and the TPS2350 RTN pin, as shown in the Typical Application
diagram. A 75-V to 100-V rated device (VRRM), such as MMBD4148 or BAV19, is recommended.
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