Datasheet

( )
( )
-
- ´
UV_L
5
UV_L OV_L
1.4 × R1 × V
R3 =
V 1.4 V + 10 × R1
( )
´
-
REF
XVLO (TOP)
XV_L REF
V
R = R
V V
TPS2394
SLVSAA9 –AUGUST 2010 www.ti.com
(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
Referring to Figure 10a, Equation 10 and Equation 11 produce R2 = 4.909 kW (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 almost
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 10b. 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 10b) 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 TPS2394 against reverse polarity supply connections or
input transients. If the potential at SOURCE 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 TPS2394 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.
14 Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): TPS2394