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| LTC3714_15 Datasheet, PDF (21/28 Pages) Linear Technology – Intel Compatible, Wide Operating Range, Step-Down Controller with Internal Op Amp | |||
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LTC3714
Applications Information
Next, choose the synchronous MOSFET switch. Because
of the narrow duty cycle and large current, a single SO-8
MOSFET will have difficulty dissipating the power lost in
the switch. Choosing two IRF7811s (RDS(ON) = 0.013Ω,
CRSS = 60pF) yields a nominal sense voltage of:
VSNS(NOM) = (15A)(0.5)(1.3)(0.013Ω) = 127mV
Tying VRNG to INTVCC will set the current sense voltage
range for a nominal value of 140mV with current limit
occurring at 186mV. To check if the current limit is ac-
ceptable, assume a junction temperature of about 100°C
above a 50°C ambient with Ï150°C = 1.6:
ILIMIT
â¥
(0.5)
186mV
(1.6) (0.013Ω)
+
1
2
(5.4A)
=
20A
and double check the assumed TJ in the MOSFET:
PBOT
=
24V â 1.15V
24V
â20 A
ââ 2
â2
â â
(1.6 ) (0.013Ω)
=
1.98 W
â
TJ = 50°C + (1.98W)(50°C/W) = 149°C
CSS
0.1µF
CC1
2.2nF RC
20k
CION 0.01µF
CFB 100pF
RON
330k
9 VID2
VID1 8
10 RUN/SS
VID0 7
11 VON
RPG
100k 12
PGOOD
BOOST 6
TG 5
DB
CMDSH-3
CB
0.33µF
13 VRNG
SW 4
14 ITH
3
SENSE
CC2
100pF 19
LTC3714
2
SGND
PGND
21 ION
BG 1
22 VFB
28
INTVCC
20 FCB
27
VIN
23 VOSENSE EXTVCC 26 5V
24 VID3
VID4 25
CVCC
4.7µF
RF
1â¦
CF
0.1µF
15
OPVIN
16 OP â
OPOUT 18
OP + 17
M1
L1
IRF7811 0.68µH
M2
IRF7811
Ã2
D1
UPS840
CIN
22µF
25V
Ã3
COUT
270µF
2V
Ã5
VIN
7V TO 24V
VOUT
1.15V
15A
CIN: UNITED CHEMICON THCR70EIH226ZT
COUT: PANASONIC EEFUE0D271
L1: SUMIDA CEP125-4712-T007
3714 F08
Figure 8. CPU Core Voltage Regulator 1.15V/15A at 300kHz without Active Voltage Positioning
3714f
21
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