LTC3719EG Linear Technology, LTC3719EG Datasheet - Page 24

• Manufacturer Part Number: LTC3719EG
• Description: IC SW REG SYNC STEP-DOWN 36-SSOP
• Manufacturer: Linear Technology

Specifications of LTC3719EG

• Applications: Controller, AMD Opteron™
• Voltage - Input: 4 ~ 36 V
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 1.55 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
LTC3719
Design Example
As a design example, assume V
(max), V
The inductance value is chosen first based on a 30% ripple
current assumption. The highest value of ripple current
occurs at the maximum input voltage. Tie the FREQSET pin
to the INTV
inductance for 30% ripple current is:
A 1 H inductor will produce 31% ripple current. The peak
inductor current will be the maximum DC value plus one
half the ripple current, or 11.5A. The minimum on-time
occurs at maximum V
The R
maximum current sense voltage specification with some
accomodation for tolerances:
The power dissipation on the topside MOSFET can be
easily estimated. Using a Siliconix Si4420DY for example;
R
voltage with T
temperature:
24
DS(ON)
R
L
t
ON MIN
SENSE
SENSE
1 04
V
f L
300
.
OUT
OUT
= 0.013 , C
CC
kHz
resistors value can be calculated by using the
= 1.2V, I
H
50
11 5
J
1
V
(estimated) = 110 C at an elevated ambient
pin for 300kHz operation. The minimum
V f
1 2
OUT
mV
.
IN
.
30
V
A
V
V
U
OUT
IN
MAX
%
IN
RSS
0 004
10
5 5
:
.
= 20A, T
.
U
A
= 300pF. At maximum input
V
1 2
IN
.
1
300
= 5V (nominal), V
V
A
= 70 C and f = 300kHz.
1 2
5 5
kHz
W
.
.
V
V
0 73
.
U
IN
s
= 5.5V
The worst-case power disipated by the synchronous
MOSFET under normal operating conditions at elevated
ambient temperature and estimated 50 C junction tem-
perature rise is:
A short-circuit to ground will result in a folded back current
of about:
The worst-case power disipated by the synchronous
MOSFET under short-circuit conditions at elevated ambi-
ent temperature and estimated 50 C junction temperature
rise is:
which is less than normal, full-load conditions. Inciden-
tally, since the load no longer dissipates power in the
shorted condition, total system power dissipation is de-
creased by over 99%.
The duty factor for this application is:
P
P
I
P
DF
SC
MAIN
SYNC
SYNC
V
0 004
V
25
IN
O
.
0 013
1 2
1 5
5 5
300
696
5 5
5 5
.
mV
.
.
.
.
.
V
V
W
1 2
V
V
5 5
5 5
kHz
mW
5
.
.
.
V
10 1
V
V
V
1 2
1 2
2
1
.
.
2
1 7 5 5
V
V
0 24
.
200
0 45
.
2 10
.
6 8
.
.
ns
1
0 005 110
W
A
.
V
A
H
5 5
2
2
2
.
1 48 0 013
10
1 48 0 013
V
.
.
A
300
6 8
C
.
.
.
pF
A
25
sn3719 3719fs
C