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LTC3865 Datasheet, PDF (32/36 Pages) Linear Technology – Dual, 2-Phase Synchronous DC/DC Controller with Pin Selectable Outputs | |||
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LTC3865/LTC3865-1
Applications Information
A short-circuit to ground will result in a folded back cur-
rent of:
ISC
=
(1/ 3)50mV
0.008â¦
â
1
2

ï£ï£¬
90ns(20V)
3.3µH 
=
1.8
A
with a typical value of RDS(ON) and d = (0.005/°C)(20)
= 0.1. The resulting power dissipated in the bottom
MOSFET is:
PSYNC
=
20V â 3.3V
20V
(1.8A)2
(1.125)(0.016â¦)
= 48mW
which is less than under full-load conditions.
CIN is chosen for an RMS current rating of at least 2A at
temperature assuming only channel 1 or 2 is on. COUT is
chosen with an ESR of 0.02⦠for low output ripple. The
output ripple in continuous mode will be highest at the
maximum input voltage. The output voltage ripple due to
ESR is approximately:
VORIPPLE = RESR (âIL) = 0.02â¦(1.5A) = 30mVP-P
TYPICAL APPLICATIONS
10µF
2.2â¦
35V
1µF
VIN
10µF
+ 22µF 4.5V TO 24V
35V
50V
L2
0.47µH
D1
Q1
RJK0305DPB
4.7µF
0.1µF
Q2
RJK0330DPB
100â¦
2mâ¦
1000pF
VOUT1
1.5V
15A
+
COUT2,3
COUT1
100µF
100â¦
1000pF
10k 100pF
D1, D2: VISHAY B340A
L1, L2: VISHAY IHLP4040DZERR47M11
COUT1, COUT4: TDK C322JX5R0J107MT
COUT2, COUT3, COUT5, COUT6: SANYO 4TPE 220µF
D3 VIN PGOOD EXTVCC INTVCC
TG1
TG2
BOOST1
BOOST2
SW1
SW2
LTC3865
BG1
BG2
MODE/PLLIN
ILIM
SENSE1+
PGND
FREQ
SENSE2+
RUN1
SENSE1â
VID11
VID12
VOSENSE1
ITH1
TK/SS1
SGND
RUN2
SENSE2â
VID21
VID22
VOSENSE2
ITH2
TK/SS2
0.1µF 0.1µF
D4
0.1µF
Q3
RJK0305DPB
Q4
RJK0330DPB
100â¦
1000pF
100â¦
1000pF
+
COUT5,6
162k 15k
1%
100pF
L2
0.47µH
D2
2mâ¦
VOUT2
1.2V
15A
COUT4
100µF
3865 F16
Figure 16. 1.5V/15A, 1.2V/15A Converter Using Sense Resistors
3865f
32
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