TPS2560_15 Datasheet, PDF (14/29 Pages) Texas Instruments – Dual Channel Precision Adjustable Current-limited Power Switches

TPS2560, TPS2561
SLVS930B – DECEMBER 2009 – REVISED DECEMBER 2015
www.ti.com
10.2.2 Detailed Design Procedure
10.2.2.1 Input and Output Capacitance
Input and output capacitance improves the performance of the device; the actual capacitance should be
optimized for the particular application. For all applications, a 0.1μF or greater ceramic bypass capacitor between
IN and GND is recommended as close to the device as possible for local noise decoupling. This precaution
reduces ringing on the input due to power-supply transients. Additional input capacitance may be needed on the
input to reduce voltage overshoot from exceeding the absolute maximum voltage of the device during heavy
transient conditions. This is especially important during bench testing when long, inductive cables are used to
connect the evaluation board to the bench power supply.
Output capacitance is not required, but placing a high-value electrolytic capacitor on the output pin is
recommended when large transient currents are expected on the output.
10.2.2.2 Programming the Current-Limit Threshold
The overcurrent threshold is user programmable via an external resistor, R_ILIM. R_ILIM sets the current-limit
threshold for both channels. The TPS256x use an internal regulation loop to provide a regulated voltage on the
ILIM pin. The current-limit threshold is proportional to the current sourced out of ILIM. The recommended 1%
resistor range for R_ILIM is 20 kΩ ≤ R_ILIM ≤ 187 kΩ to ensure stability of the internal regulation loop. Many
applications require that the minimum current limit is above a certain current level or that the maximum current
limit is below a certain current level, so it is important to consider the tolerance of the overcurrent threshold when
selecting a value for R_ILIM. The following equations calculates the resulting overcurrent threshold for a given
external resistor value (R_ILIM). The traces routing the R_ILIM resistor to the TPS256x should be as short as possible
to reduce parasitic effects on the current-limit accuracy.
I_OSmax (mA) =
52850V
R_ILIM0.957kW
I_OSnom (mA) =
56000V
R_ILIMkW
I_OSmin (mA) =
61200V
R_ILIM1.056kW
(1)
3000
2750
2500
2250
2000
1750
1500
1250
1000
750
500
250
0
20
I_OS(typ)
I_OS(min)
I_OS(max)
30 40 50 60 70 80 90 100 110 120 130 140 150
R_ILIM – Current Limit Resistor – kΩ
Figure 19. Current-Limit Threshold vs R_ILIM
14
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