[time-nuts] ULN regulator with more current capability than LT3042?

[John Miles]

> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of John
> Ackermann N8UR
>
> Reviving the conversation about superb voltage regulators, I am looking
> for one to run the analog and PLL bits of a high performance frequency
> synthesizer chip.
> 
> The current drain looks to be about 160-180 mA at 1.8 V, which is
> uncomfortably close to the limit for the LT3042 (200 mA).  The
> manufacturer's evaluation board uses a MAX8869, which appears to be
> nowhere in the LT3042's league, but will source 1 A.
> 
> Any recommendations for a 1.8 V regulator a little beefier than the
> LT3042, but with similar noise performance?

These days, the best RF synthesizer and clock generator chips include dedicated low-noise LDOs inside the package.  It's rarely worthwhile to use a quieter regulator than the manufacturer recommends, or one that's quieter than whatever is on their own demo board. 

One very nifty example is the LMK61E2, which I X-rayed a while back:
http://www.ke5fx.com/LMK61E2_30kVp_20s.png

The overall package is only about 1 cm square.  The synthesizer has its own die, while the input regulators and (presumably) their bypass caps are mounted directly above the Vdd input pad.  According to TI, the PSRR of the internal LDO that runs the analog section is better than 70 dB at offsets below 1 MHz.  So you could even power it directly from a switcher, assuming you keep a leash on its harmonics. 

-- john, KE5FX
Miles Design LLC