Boosting bootstrap pin on sync buck

[Phil Hobbs]

So we got these nice little laser controller boards back from the
assembler. (Super low noise, 150 mA drive, > 20 dB below the shot
noise, digital control loops for constant laser power and temperature
control. It uses the LPC845, a nice little Cortex M0+ that we're using
more and more often. It runs at 30 MHz, and has both a single-cycle
integer multiply and a microprogrammed integer divide. Maybe its best
feature is a giant pin mux, so that you can have any peripheral function
anywhere, apart from the ADC and stuff like ~RESET and ISP. That
simplifies layout by a lot.

It runs off +5 and ground, so it has a boost converter to power the
laser and a buck for the TEC. Both run at 2.15 MHz, synched by a MCU
clock output.

The TEC driver runs Class H, with a very simple voltage control
loop--gradually ramp down the supply voltage till the amp can't quite
supply the requested current, then bump it up by 150 mV. That inner
loop runs faster than the temperature controller, so the outer loop
tracks out the minor nonlinearity that results.

The buck is an LMR23630, which can supply 3A but drops almost a volt
doing it from 5V. Awkward.

Just on spec, I put a 10k resistor from the bootstrap pin of the 23630
to the +13.5V boost output, and the voltage drop improved by almost 200
mV, which is over half a watt of dissipation at 3A. Another one for the
tool box.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Larkin]

On Thu, 25 Jul 2019 12:23:50 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

So we got these nice little laser controller boards back from the
assembler. (Super low noise, 150 mA drive, > 20 dB below the shot
noise, digital control loops for constant laser power and temperature
control. It uses the LPC845, a nice little Cortex M0+ that we're using
more and more often. It runs at 30 MHz, and has both a single-cycle
integer multiply and a microprogrammed integer divide. Maybe its best
feature is a giant pin mux, so that you can have any peripheral function
anywhere, apart from the ADC and stuff like ~RESET and ISP. That
simplifies layout by a lot.

It runs off +5 and ground, so it has a boost converter to power the
laser and a buck for the TEC. Both run at 2.15 MHz, synched by a MCU
clock output.

The TEC driver runs Class H, with a very simple voltage control
loop--gradually ramp down the supply voltage till the amp can't quite
supply the requested current, then bump it up by 150 mV. That inner
loop runs faster than the temperature controller, so the outer loop
tracks out the minor nonlinearity that results.

The buck is an LMR23630, which can supply 3A but drops almost a volt
doing it from 5V. Awkward.

Just on spec, I put a 10k resistor from the bootstrap pin of the 23630
to the +13.5V boost output, and the voltage drop improved by almost 200
mV, which is over half a watt of dissipation at 3A. Another one for the
tool box.

Cheers

Phil Hobbs

Neat. The 23630 bootstraps the drive to the upper nfet by less than 4
volts, which is pretty wimpy. I wonder if you could connect Vcc to +5.

I use a lot of tiny TPS54302 sync switchers, SOT23 with no power pad,
which are rated for 3 amps, but get awfully hot at 3, so I restrict
them to 2 amps. Maybe a bit more bootstrap voltage would help.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Tim Williams]

I did that on a recent design that needed 0-100% duty cycle range, high
side. Just put in a "bleeder" resistor from BS to Vin, and one from Vout to
GND. And a TVS from S to BS to ensure it doesn't overvolt.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:ALydnQi71rcESqTAnZ2dnUU7-VvNnZ2d@supernews.com...

So we got these nice little laser controller boards back from the
assembler. (Super low noise, 150 mA drive, > 20 dB below the shot noise,
digital control loops for constant laser power and temperature control.
It uses the LPC845, a nice little Cortex M0+ that we're using more and
more often. It runs at 30 MHz, and has both a single-cycle integer
multiply and a microprogrammed integer divide. Maybe its best feature is
a giant pin mux, so that you can have any peripheral function anywhere,
apart from the ADC and stuff like ~RESET and ISP. That simplifies layout
by a lot.

It runs off +5 and ground, so it has a boost converter to power the laser
and a buck for the TEC. Both run at 2.15 MHz, synched by a MCU clock
output.

The TEC driver runs Class H, with a very simple voltage control
loop--gradually ramp down the supply voltage till the amp can't quite
supply the requested current, then bump it up by 150 mV. That inner loop
runs faster than the temperature controller, so the outer loop tracks out
the minor nonlinearity that results.

The buck is an LMR23630, which can supply 3A but drops almost a volt doing
it from 5V. Awkward.

Just on spec, I put a 10k resistor from the bootstrap pin of the 23630 to
the +13.5V boost output, and the voltage drop improved by almost 200 mV,
which is over half a watt of dissipation at 3A. Another one for the tool
box.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com