LMC7660 Output Current

I looked at Figure 4 and from what I understand, it describes the voltage drop at the output given a +5V input at different load currents. For example, when tracing the curve, a drop of -5V to -4V (by 1 volt) will occur due to a 20mA load current.

If my understanding is correct, then please inform me.

I think that is correct. These charge pumps are intended for very light load in the rang of 1 mA or so.

In this case, could you please recommend me an alternative part form TI that can support a little heavier load (Min of 2mA @ 0.1V max drop) across a wide temperature range?

I am trying to be careful here because I am using this charge pump to provide a negative supply to ADS1220's AVSS which is rated for a maximum of -2.3V. In addition, I am using it to supply TI's OP AMP (TLV333) as a part of bipolar spply (+2.5V and -2.5V). I want to make sure that at the very worst case, charge pump would maintain a regulation no higher than -2.4V.

I don't really know those parts very well. Let me see if I can find someone who does.

Dear John and others,

I hope that, if you can, you address the following concerns I have regarding this part:

As I said before, I am using LMC7660 to provide a -2.5 supply rail to ADS1220 and TLV2333. The +2.5V supply rail fed to charge pump is coming from TLV7132 (2.5V LDO).  To check maximum load current of this -2.5V rail, I  referred to datasheet of ADC and OP AMP and came with the following information:

TLV2333's IQ = 28μA (MAX)  

, and assuming this consumption per amp ---->  IQ= 28×2 = 56μA ,

, and since it's driving a light load (input of ADS1220 with PGA disabled) ----> IQ + load current <= 100μA (WORST CASE)

ADS1220's Ivdd (analog supply current @ Turbo mode, PGA disabled) =~ 400μA  ---> pump it up to 500μA

TOTAL CONSUMPTION = 100 + 500 = 600μA

My only concern now is that since I am using a bipolar power supply for ADS1220 (+2.5V, -2.5V), I am worried that charge pump's voltage drop @ 600μA, in addition to output ripple might at some point exceed ADS1220's maximum rated supply for AVSS, which -2.3V.

From LMC7660's datasheet, graph of output voltage vs. load current shows that at my load current (600μA), voltage drop will not even reach 0.1V, which is a good thing, but what about ripple? is there an equation to calculate the expected amount of ripple at the output? I found the following equation from TL7660's datasheet, but I am not sure if it's applicable:

Given the pumping frequency of LMC7660 (10KHz), C2 = 10μF, ESR OF C2 = 2.5, Iout = 600μA

,then peak-to-peak ripple =~ 116μV

What do you think? is there anything wrong or missing here?

Thanks,

Abdullah