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TPS2592BA Datasheet, PDF (21/34 Pages) Texas Instruments – 5-V eFuse with Over Voltage Protection and Blocking FET Control
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10.2.2.1 Design Requirements
TPS2592BA, TPS2592BL
SLVSCU2 – DECEMBER 2014
Table 3. Design Parameters
DESIGN PARAMETER
Input voltage range, VIN
Undervoltage lockout set point, V(UV)
Overvoltage protection set point , V(OV)
Load at Start-Up , RL(SU)
Current limit, IOL= IILIM
Load capacitance , COUT
Maximum ambient temperatures , TA
EXAMPLE VALUE
5V
4.5 V
Default: VOVC = 6.1 V
1000 Ω
3A
4700 µF
85°C
10.2.2.2 Detailed Design Procedure
10.2.2.2.1 Programming the Current-Limit Threshold: RILIM Selection
The RILIM resistor at the ILIM pin sets the over load current limit, this can be set using Equation 4.
For IOL= IILIM = 3 A, from equation 4, RILIM = 76.8 kΩ, choose closest standard value resistor with 1% tolerance.
10.2.2.2.2 Undervoltage Lockout Set Point
The undervoltage lockout (UVLO) trip point is adjusted using the external voltage divider network of R1 and R2 as
connected between IN, EN/UVLO and GND pins of the device. The values required for setting the undervoltage
are calculated solving Equation 5.
For UVLO of V(UV) = 4.5 V, select R2 = 453 kΩ, and R1 = 1 MΩ.
The power failure threshold is detected on the falling edge of supply. This threshold voltage is 4% lower than the
rising threshold, V(UV). This is calculated using Equation 6.
Where V(UV) = 4.5 V, Power fail threshold set is : V(PFAIL) = 4.33 V
10.2.2.2.3 Setting Output Voltage Ramp Time (TdVdT)
For a successful design, the junction temperature of device should be kept below the absolute-maximum rating
during both dynamic (start-up) and steady state conditions. Dynamic power stresses often are an order of
magnitude greater than the static stresses, so it is important to determine the right start-up time and in-rush
current limit required with system capacitance to avoid thermal shutdown during start-up with and without load.
For the design example under discussion, select ramp-up capacitor CdVdT = 22 nF. Then, using Equation 2.
TdVdT = 106 x 5 x (22 nF + 70 pF) = 110 ms
(18)
The inrush current drawn by the load capacitance (COUT) during ramp-up using Equation 7.
I(INRUSH)
= 4700
mF x
5
110 ms
= 213 mA
(19)
The inrush Power dissipation is calculated, using Equation 8.
PD(INRUSH) = 0.5 x 5 x 213 m = 533 mW
(20)
Considering the start-up with load 1000 Ω, the additional power dissipation, when load is present during start up
is calculated, using Equation 9.
PD(LOAD)
=
6
5x5
´ 1000
= 4.2 mW
(21)
The total device power dissipation during start up is:
PD(STARTUP) = 533 + 4.2 = 537 mW
(22)
From thermal shutdown limit graph at TA = 85°C, the thermal shutdown time for 537 mW is more than 300 ms.
So the device will start safely.
Copyright © 2014, Texas Instruments Incorporated
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