LTC3626_15 Datasheet, PDF (23/28 Pages) Linear Technology – 20V, 2.5A Synchronous Monolithic Step-Down Regulator with Current and Temperature Monitoring

LTC3626
Applications Information
Next, determine the inductor value for approximately 40%
ripple current using:
L
=
⎛⎝⎜_1M1H.8z V_{• 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 –
12V
1.8V₎
=
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.
V_IN
12V
C_IN1
C_IN2
47µF
1µF _R3
C3
PV_IN
SV_IN
RUN
BOOST
C_BST
5Ω
0.33µF
LTC3626
0.1µF
L1
C_INTVCC
2.2µF R_TSET1
432k
R_PGD
100k
INTV_CC
TRACK/SS
SW
ITH
MODE/SYNC V_ON
IMON_IN
PGOOD
FB
1.5µH
C_F
R1
22pF
40.2k
C_OUT
47µF
V_OUT
1.8V
2.5A
TMON
R2
TSET
RT
20k
R_TSET2
665k
C_IOUT
1µF
IMON_OUT
R_IOUT ^SGND
7.68k
PGND
R_T
324k
3626 F07
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
For more information www.linear.com/LTC3626
3626fa
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