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Honest Reviews: FAN48610 - Fairchild Semiconductor's Not-Programmable TinyBoost Regulator

It is nice not to hear any unreferenced superlatives in the short description of Fairchild Semiconductor's TinyBoost regulator, the counterpart of their TinyBuck regulator. For completion, I review FAN48610, being even smaller than TinyBuck but with a lower output current capacity (as expected from a boost)  and no trimming feature.

FAN48610 or TinyBoost (mind if I call it by its family name for the rest of the article) is "a low-power boost regulator designed to provide a minimum voltage regulated rail from a standard single-cell Li-ion battery and advanced battery chemistries" according to FS. A boost regulator, which serves the opposite function of a buck regulator, steps up the input voltage by essentially taking advantage of the inductor's ability to resist current change. It is available in a 1.215mm by 1.215mm WLCSP package, with 0.4mm pitch (datasheet available for download by following the link below).
Download TinyBoost's DataSheet 

DataSheet Analysis

Based on the data sheet, the input voltage range is from 2.5V to 4.5V, which is typical. TinyBoost isn't programmable, so it provides an output voltage directly proportional to VIN. With a VIN of 3.6V, the expected output voltage should be 5V given the setup below (Fig.1):

Figure 1. Typical application set-up of FAN48610


 It is worth noting that CIN (10uF) and COUT (22uF) should be placed as close to TinyBoost as possible. Capacitors are usually placed at the input and output sides in application because the input capacitor helps attenuate  input voltage transients, the output capacitor helps attenuate load transients, and both help couple AC noise and interference to ground.

Speaking of inductors and capacitors, the suggested suppliers for inductors and capacitors are Toko and Murata respectively. They are both reputable, based on experience. Reputable in the sense that you'd get better transient responses out of them, and the capacitance values don't drift too much with frequency and temperature.


A maximum efficiency of 94%, at input voltages above 3.6V

TinyBoost has a maximum efficieny of up to 94%.





Figure 2. Efficiency curves of FAN48610 against input voltage, temperature and load current
Based on the curves, 94% maximum efficiency is only plausible at input voltages greater than 3.6V. At 2.6V, we can only expect a maximum efficiency of around 90%. As expected, colder temperature yields higher efficiency from the curve at the right.



Also, a soft start feature is added to protect internal circuitry from sudden bursts of current at the input. This scenario becomes very probable when the capacitance seen at VOUT is significantly high.


Shown below are TinyBoost's block diagram, pin configuration, and recommended layout.
Figure 3. Block diagram of FAN48610

An enable signal is fed to the logic circuit of TinyBoost, which signals the rectifier control to drive the pass transistor towards the triode region, thus "enabling" the circuit.

Figure 4. Pin configuration of FAN48610


Fewer balls, fewer features.


Figure 5. Layout recommendation for FAN48610

You'd normally connect your sense lines to PGND and force lines to AGND. But in the provided layout recommendation, they no longer considered this detail, maybe because its connected to a ground plane anyway. Obviously, the practice of connecting the capacitors as close as possible to the chip is implemented.

Figure 6. Load regulation of FAN48610


From the load regulation curves, the output perseveres from no load all the way to 1 A regardless of the condition.

Figure 7. Quiescent current vs. VIN of FAN48610

 The quiescent current is a bit higher than normal just like TinyBuck, but FS boasted something right beside it:
Figure 8. Output ripple vs. load current of FAN48610


 This is nice. They have managed to achieve an output ripple as small as 20 mVpp for a switching regulator, which is unusually quiet. Ordinary regulators would have an average ripple of 80 mVpp.

Figure 9. Switching frequency vs. load current of FAN48610

 When a switching regulator reaches its maximum rated load, one would expect the output to become DC (i.e. no frequency, no duty cycle). So the output still has a broad margin beyond the 1A load capacity, since the output is still switching at 1A. (probably 1.5A)

A load transient way higher than TinyBuck

Figure 10. Load response of FAN48610 on a 100-500mA pulse with 100ns rise/fall time

Sadly, TinyBoost's load transient is higher - around 100mV (but still under tolerable limits), than TinyBuck's 30-50mV load response from a 1-1.5A load.

The last characteristic of TinyBoost worth mentioning is its maximum current ability with respect to input voltage.

Figure 11. Current ability vs. VIN of FAN48610

So TinyBoost is capable of a maximum 2.6A at a VIN of 4.5V at typical temperature (current ability decreases at hotter temperatures - an inviolable law I think, never saw a load regulation with an output that dropped earlier than the curve with a hotter temp.)


To conclude, TinyBoost is a small 5V 1A switching boost regulator, capable of a max 2.6A load at VIN=4.5V and 94% efficiency at VIN>3.6V. I could not test it against a variety of battery chemistries, so its something I'll have to leave for commercial buyers to test on.

 

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