Paralleled MAX889

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I have, already, contacted technical support and have no answer, yet. To generalize the question : Can any Switched Capacitor Charge Pump with output voltage regulation be paralleled?

Most likely, the answer would be not to do so in order to achieve a better regulation. However, I think, there shouldn't be any reason not to.

Hi StevenStanleyBayes,  Please tell me which regional support team you submitted a ticket to? If you provide some details, we will follow up with the support team to understand the delay in response. Thank you - Geneva

Thank for your help. I received a reply from Analog Devices, which, is of enormous help. I am, still, in communication with them and will post their answer, when, I got more information.

I have received an answer and would like to post the answer for whoever is interested :

1. There is no limit for any of the capacitors. For the flying capacitor, the value can be 100uF. I prefer 330uF, Solid State, Lowest ESR || 10uF Ceramic || 0.1uF Ceramic, X7R. Another approach may be to use 10 fold what the datasheet recommends. The basic rule : the capacitor may not fully charge from 0 to maximum in one cycle, but, then, the capacitor will not fully discharge and after a transient process, the capacitor will reach steady state regime and rub at the desired voltage. The input and the output capacitor can be 1.5mF, Solid State || 10uF Ceramic || 0.1uF Ceramic, X7R || to as many Ceramics as possible, as many X7R as possible : 10uF || 1uF || 0.1uF || 10nF || 1nF || 100pF || 10pF || 2pF. The same applies to the flying capacitor.

2. MAX889 and other REGULATED inverters and power supply devices are not recommended to parallel. The feedbacks may fight. I, personally, think, they would be OK, but, this opinion is not important. DO NOT! Of course, there is, always, a way to parallel batteries and any, other, power supply devices with diodes or even Schottky diodes. This will lower the voltage, but, in some cases, this is not important. The paralleled devices can be fed with 5V to make - 4.3V ( nominal ) after the diode. A diode can be installed on the 5V input to make 4.3V ( nominal ) output. Thus, there would be a + - 4.3V, somewhat regulated, which is OK in most cases. The forward voltage of the diodes, however, depend on the forward current and temperature and may vary between <= 0.5V and >= 2V. The diodes may be before the feedbacks, in some cases. This will ensure regulation.

3. MAX889, MAX168x and other have a VERY LIMITED CURRENT, because of their limited power dissipation to 471mW at 70C. This allows for around 40mA with MAX1680. MAX889 in regulation will provide more current then when not in regulation, because, of the lower current consumption. The advertised currents of 125mA and 200mA are NOT applicable. Maybe, only, at the lowest, possible, voltage for the devices to run, but, definitely, NOT for the standard 5V. Also, the higher the frequency, the higher the consumed ( quiescent ) current, the lower the input current. All this because of surface mount stupidity. Maxim should make these parts in T)220 style, multi pin package with case, connected to ground, so, they can be mount on the chassis. DIP is easily possible and allows for, nearly, double the power.

4. I have decided on this solution : parallel 7 MAX1680 to make around 300mA. Make FSEL selectable with a jumper for a higher versatility. Then make a voltage regulator to get 3.3V from 5V and - 3.3V from - 5V. These can be made with pass through transistors ( common emitter ). However, the best is to use a common collector buffer. Thus : 3.3V voltage reference with LM431 with heavy, output capacitors, then a heavy, passive RC filter, then a buffer, then, another, heavy, passive RC filter, then a buffer with a buffer transistor before the feedback. This will give 3.3V. From the output of the first buffer, put an inverting filter amplifier, then, a heavy, passive RC filter then, another, buffer with a buffer transistor before the feedback. Ensure the amplifiers are rail to rail input and output. Pay attention : manufacturers advertise rail to rails and they are not. Their maximum and minimum output voltages depend heavily on the output current. Most can reach very near the rails at 5uA. These can get to 1V away from the rails at around 10mA. Some are much better and can get to 33mA. Ensure the output transistors are Toshiba. They are the best, the lowest noise and the highest Beta.