Datasheet

SLUU171A - September 2003
19
TPS2350 −48-V Hot Swap/Supply Selector Evaluation Module
The thresholds are easily modified by changing the resistor values. When the desired trip voltages and the UV
hysteresis have been established for the protected load, new values are determined as follows. Generally, the
process is simplest by first selecting the top leg of the divider (R1) needed to obtain the desired hysteresis. This
value is calculated from equation 4.
R1 +
V
HYS_UV
10 mA
where V
HYS_UV
is the desired amount of undervoltage hysteresis.
Once a value for R1 is selected, it is used to calculate R2 and R3 using equations 5 and 6.
R2 +
1.4 R1
ǒ
V
UV_L
* 1.4
Ǔ
ȧ
ȱ
Ȳ
1 *
V
UV_L
ǒ
V
OV_L
) 10
*5
R1
ȧ
ȳ
ȴ
R3 +
1.4 R1
ǒ
V
UV_L
* 1.4
Ǔ
ȧ
ȱ
Ȳ
V
UV_L
ǒ
V
OV_L
) 10
*5
R1
ȧ
ȳ
ȴ
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
4.8 TPS2350 Powergood Output (PG)
The supply selector EVM features two nodes to access the powergood status generated by the TPS2350. For
simply monitoring, for example with a scope probe, the actual output signal itself is available at test point TP12.
The MOD_EN output at J7 demonstrates an isolated signal interface using an opto device. An example
application of such a signal is to drive the enable input of downstream converters. As such, this output is
referenced to the VOUT− node, as this would be the low side of input power to the brick. The EVM schematic
shows the circuit details. The MOD_EN assertion level is active-high. The use of this signal requires a pull-up
source at the VS input, J6. See Tables 2 and 3 for the requirements of the VS supply.
(4)
(5)
(6)