Datasheet

LTC3626
23
3626f
APPLICATIONS INFORMATION
Next, determine the inductor value for approximately 40%
ripple current using:
L =
1.8V
1MHz • 1A






1–
1.8V
12V






= 1.53µH
A standard 1.5µH inductor will work well for this application.
Next, C
OUT
is selected based on the required output tran-
sient performance and the required ESR to satisfy the
output voltage ripple. For this design, two 22µF ceramic
capacitors will be used.
C
IN
should be sized for a maximum current rating of:
I
RMS
= 2.5A •
1.8V 12V – 1.8V
( )
12V
= 0.89A
Decoupling the PV
IN
pin with a 47µF ceramic capacitor
should be adequate for most applications. An additional
1µF capacitor on the PV
IN
can be used to help reduce
ringing as required. A 0.33µF capacitor on the SV
IN
pin is
optional and will be tied to PV
IN
through a 5Ω resistor for
additional filtering at the SV
IN
pin. Finally, a 0.1µF boost
capacitor should work for
most applications.
To save board space, the ITH pin is connected to INTV
CC
to select the internal compensation network.
The PGOOD pin is connected to V
IN
through a 100k resis-
tor to INTV
CC
.
To program the I
OUT
limit at 2.5A, a resistor is connected
between IMON
OUT
and SGND with a desired value equal to:
R
IOUT
=
16,000 • 1.2V
2.5A
= 7.68kW
Thus, a standard 7.68kΩ will be selected for R
IOUT
. A 1µF
capacitor placed in parallel with R
IOUT
for I
OUT
limit loop
compensation should be adequate for most applications.
The 125°C temperature limit is programmed by setting a
voltage at the TSET pin equal to:
V
TSET
=
125°C+ 273
200°K/V
≈ 2V
In this example, the TSET voltage will be derived by divid-
ing the available INTV
CC
voltage using R
TSET1
= 432k and
R
TSET2
= 665k.
PV
IN
SV
IN
RUN
BOOST
SW
V
ON
FB
RT
INTV
CC
TRACK/SS
ITH
MODE/SYNC
IMON
IN
PGOOD
TMON
TSET
IMON
OUT
SGND PGND
LTC3626
C
IN2
1µF
C
IN1
47µF
R3
5Ω
C3
0.33µF
V
OUT
1.8V
2.5A
V
IN
12V
R
IOUT
7.68k
C
IOUT
1µF
C
INTVCC
2.2µF
C
BST
0.1µF
C
F
22pF
C
OUT
47µF
L1
1.5µH
R
TSET2
665k
R
TSET1
432k
R1
40.2k
R2
20k
R
PGD
100k
3626 F07
R
T
324k
Figure 7. 12V Input to 1.8V Output, 2.5A Regulator at 1MHz in Burst Mode Operation with
Output Current Monitor and 2.5A Limit, On-Die Temperature Monitor and 125°C Limit