From the 1580 data sheet.
"To achieve this dropout, a second low current input voltage 1V greater
than the output voltage, is required."
Like I said, ship it with a battery. ;-)
Then the "normal" part can have a dropout of 1.4V. You can't fight the
physics of the topology. For a NPN pass device, you need a Vbe of a NPN
and at the very least a PNP Vcesat. That is not low dropout, especially
at cold.
On 2/28/2012 7:30 AM, David wrote:
The Linear Technology LT3070 (150mV @ 5A) , LT3071, LT1580 , and
LT1581 (700 mV @ 10A) are examples:
http://www.linear.com/product/LT1580
For comparison:
http://www.linear.com/product/LT1584
The LT1580 (0.8V @ 7A) has the same topology as the LT1584 (1.5V @ 7A)
except everything but the pass NPN is powered from a bias supply
brought out to a separate pin. If the bias supply is connected to the
input supply, then it duplicates the dropout characteristics of the
LT1584.
On Mon, 27 Feb 2012 22:58:33 -0800, gary<[email protected]> wrote:
I hate to be argumentative, but you can't be low drop out and use an
emitter follower. Draw the circuit and convince yourself. You would need
a high side driver scheme to drive the base/gate, and that require some
sort of boost converter. It can be done on switchmode chips, but not in
a linear circuit. Well unless you ship it with a battery.
On 2/27/2012 9:51 PM, David wrote:
The highest performance low dropout regulators I have seen use
emitter/source followers with a low current bias supply.
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