Switching (some Linear) Voltage Regulators
Here are two good application notes explaining the basics of linear and
- switching voltage regulators.
Tentative Specs:
- I [Jacob] assume the following:
- Must be buck (step-down) regualtors?
- Must use internal FET drivers?
- At least 100mA at 1.8V
- Preliminary 250mA at 3.3V
- If no 1.8V rail then 400mA at 3.3V
- Quiescent current < 15mA
- Nominal efficiency >= 80%
- Proper supply sequencing (dependent on microprocessor)
- Synchronous to external clock
- Packaging
- Avoid thermal ground pads if possible
- Avoid "weird" proprietary packaging
- Meet old requirements:
- 10 - 20V
- > 70 % efficiency (old supply was 80%+ from 10mA to full load)
- ~= existing supply size (plan area 1 sq.in. with components on both sides, i.e. 2 sq.in. total surface)
- EMI compatible with onboard communication systems (e.g., crystal oscillator locked)
- Must be able to shut down on external signal.
- Node protection:
- Undervoltage lockout
- Overvoltage protection
- Reverse polarity protection
- Bus protection:
- Current limiting (e.g., fuse)
Potential Buck Regulators
( Syc = synchronizable, SD = shutdown mode )
|
Part # |
Vin (V) |
Vo (V) |
Adj. |
Syc |
SD |
IoMax |
Iq(uA) |
F(MHz) |
Package |
Notes |
Datasheet |
|
LT1767 |
8 - 25 |
1.22 - 20 |
Y |
Y |
Y |
1.2A |
6 |
2 |
msop8 |
Used in previous node |
|
|
LT3437 |
3.3 - 60 |
3.3 - 55 |
Y |
Y |
Y |
500mA |
1 (for Burst Mode 100) |
0.2 |
dfn10 |
Burst-Mode operation |
|
|
LT1962 |
1.8 - 20 |
1.22 - 20 |
Y |
n/a |
? |
300mA |
30 |
n/a |
msop8 |
Micropower LDO Regulator (Linear) |
|
|
LT3493 |
3.6 - 36 |
Down to 0.78 |
Y |
N |
? |
1.5A |
2 |
0.75 |
Low-profile DFN |
||
|
LT1940 |
3.6 - 25 |
? |
Y |
N |
Y |
1.4A |
3800 Quiescent/ 30 Shutdown |
1.1 |
16-lead Plastic TSSOP |
Dual Output Step Down Reg. |
|
|
LT1616 |
3.6 - 25 |
? |
Y |
N |
Y |
0.6A |
< 1 |
1.4 |
6-lead SOT-23 |
||
|
MIC2207 |
2.7 - 5.5 |
Down to 1 |
Y |
N |
Y |
3A |
<= 900 |
2 |
Micropower 12-lead MLF-12 |
>94% eff. PWM Buck |
|
|
MIC2204 |
2.7 - 5.5 |
Down to 1 |
Y |
Y |
Y |
0.6A |
6.5 (disabled) |
2 |
10-lead MSOP (MM) or MLF-10 (ML) |
>95% eff. PWM Buck, Sync daisy-chain option |
|
|
MIC2202 |
2.7 - 5.5 |
Down to 0.5 |
Y |
Y |
Y |
0.6A |
< 1 (disabled) |
2 |
10-lead MSOP (MM) or MLF-10 (ML) The MLF-10 has thermal ground pad |
>95% eff. PWM Buck, Sync daisy-chain option |
Switcher Pick
Tim, Andrew and I chose to use the same switching voltage regulator LT1767 from Linear Tech (3-8-06). See the SPS Design Page.