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TLV1805: Output current

Masayoshi Takahashi
Intellectual 1530 points
Part Number: TLV1805

Hi team,

I'd like to confirm the test condition of figure 22. Maximum Continuous Current vs. Ambient Temperature. 

There are some curve when the voltage is 5V, 12V, 21V, 30V, 40V. I think these value is supply voltage. Is it correct?

I also want to confirm the typical output current of TLV1805 is 100mA.  Is there any data when 100mA output current vs. Ambient temperature?

Regards,

Yoshi

  • 0
    TI__Guru 60476 points
    Hello Yoshi,

    The output current limits at 100mA - so you may not be able to sink/source 100mA continuously. The TLV1805 was designed to provide high peak currents for short periods of time (driving gate capacitance) and low duty cycles.

    The biggest limitation is the power dissipation, particularly at the higher voltages. The SOT-23 package is not the best for getting heat out...

    The Figure 22 graph is simply back-calculating the maximum output current based on a maximum junction temperature of 150C. Remember, 150C is the Abs Max (no damage, but outside DS specs) , and 125C is the warranted limit (still meets DS specs).

    The output current vs output voltage at various temperatures is shown in figures 25-30. These graphs give you the output voltage in relation to the nearest rail at the specific output sink or source current.

    The more current and voltage across the output, the more heat is generated in the die. Since the SOT-23 package is a poor heat conductor, the die can heat up very quickly - to the point of destruction (these devices do not have thermal limiting).

    To source 100mA, according to Fig 30, there will be about 4V dropped across the output. 100mA*4V=400mW. And it gets worse as the die heats up. Multiply the power dissipated by the package thermal rating (Theta-Ja) to get the temperature rise.

    400mW * 167°C/w = 67°C die temperature rise over ambient due to that load current. So if the ambient temp is 25C, then the die temp will be 25+67= 92°C. That is getting pretty warm, and limits your maximum ambient temp to 125-92=33°C to meet specs.

    So the limiting factor is the die temp. I do not recommend sinking/sourcing such high current (>30mA) in these small packages. If high currents are needed, then an external MOSFET or transistor should be used (the TLV1805 was designed to directly drive MOSFET gates quickly).
  • 0 in reply to Paul Grohe
    TI__Intellectual 1530 points
    Hi Paul,
    Thanks for your advice quickly. I understood peak output current is 100mA and can't sink/source continuously. This is why the figures 25 - 30 didn't mention 100mA value.

    BTW, I got another question from my customer.
    The customer is referring to the design of the N-channel schematic TLV1805-Q1 EVM which has charge pump circuit.
    He would like to know how much the output current of this schematic (Figure 22)
    Could you tell me how to calculate the output current of charge pump?

    Regards,
    Yoshi
  • 0 in reply to Masayoshi Takahashi
    TI__Intellectual 1530 points
    Hi Paul,
    Could you give me your advice?
  • 0 in reply to Masayoshi Takahashi
    TI__Guru 60476 points

    Hello Masayoshi,

    Theoretically, the charge pump can deliver 10's of mA, depending on the amount of ripple that is acceptable.

    The limiting factor is the peak charging current available to charge the charge pump capacitors, and the capacitor ESR's and diode resistance.

    The charge pump circuit described here is not expected to continuously supply high currents, but supply just enough current for the comparator and pull-down resistor and keep the bypass/reservoir capacitor charged. The peak drive current to drive the gate quickly would come from the charged 10uF bypass/reservoir capacitor. The 1805 limits the peak currents to 100mA. These peak currents occur during the first cycles after power-up until the reservoir cap charges up.

    See section 4.1 of this appnote for basic charge pump output current calculations:

     http://www.ti.com.cn/cn/lit/an/slva398a/slva398a.pdf

    Please note it is a tradeoff between ripple voltage and efficiency. Nothings perfect...