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Datasheet for the part in question: http://www.ti.com/lit/ds/symlink/tps92513.pdf

So, on the pin description on page 3 it describes I_adj as: Analog current adjust pin. The voltage applied to this pin will set the current sense (ISENSE pin) voltage. The range of the ADJ pin is 180 mV to 1.8 V and the corresponding ISENSE pin voltage is the IADJ pinvoltage divided by 6.

Okay, makes sense, U_Isense = U_Iadj/6.

Typical application just saturates it with the RC circuit, as internally, Isense has a 1.8V zener, Alright.

Now, I am looking to create a lighting application that's long lasting with variable light. Dimming through the PWM output dimms the output, well, with PWM, not regulating the current. As LEDs get more efficient at lower current, I'd like an option to also drive them with lower current. I require up to 1A through my string of LEDs, but they might be driven with 100mA or less. So I was thinking of being able to switch these around; having a circuit to cut the reference voltage in half, for when I'm driving the LEDs from 100-500mA. Would it be feasible to change the reference voltage during operation? As far as I can see, it goes into a comparator, so it would just adjust the output.

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  • \$\begingroup\$ What RC circuit? What gets saturated? \$\endgroup\$
    – Andy aka
    Feb 5, 2020 at 12:45
  • \$\begingroup\$ the 10MOhm + 10nF section at the top. Slowly ramps up the voltage to 1.8V, at which the internal Zener prevents further charging as per 9.4.1 @Andyaka \$\endgroup\$
    – Overrice
    Feb 5, 2020 at 12:55
  • \$\begingroup\$ At the top of what? Post your circuit to save on comments. \$\endgroup\$
    – Andy aka
    Feb 5, 2020 at 13:13
  • \$\begingroup\$ Oh, sorry. Got lost in editing, I'm referring to Figure 13 on Page 17 of the datasheet (ti.com/lit/ds/symlink/tps92513.pdf) \$\endgroup\$
    – Overrice
    Feb 5, 2020 at 13:27

1 Answer 1

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  1. Create a resistive ladder with a zener shunt regulator. You can short selected resistors(BJT, MOSFET or analog switches) to change the effective voltage at the IADJ pin
  2. If you have a DAC in the MCU you can use it to change the voltage at the IADJ pin
  3. 2nd PWM signal to create a filtered analog Voltage using RC circuit and or an opamp as a buffer.
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