LTC3865-1_15 Datasheet, PDF (33/38 Pages) Linear Technology – Dual, 2-Phase Synchronous DC/DC Controller with Pin Selectable Outputs

LTC3865/LTC3865-1
APPLICATIONS INFORMATION
A short-circuit to ground will result in a folded back cur-
rent of:
I_SC
=
(1/ 3)50mV
0.008Ω
–
1
2
⎛
⎝⎜
90ns(20V)⎞
3.3μH ⎠⎟
=
1.8
A
with a typical value of R_DS(ON) and δ = (0.005/°C)(20)
= 0.1. The resulting power dissipated in the bottom
MOSFET is:
P_SYNC
=
20V – 3.3V
20V
(1.8A)²
(1.125)(0.016Ω)
= 48mW
which is less than under full-load conditions.
C_IN is chosen for an RMS current rating of at least 2A at
temperature assuming only channel 1 or 2 is on. C_OUT is
chosen with an ESR of 0.02Ω 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:
V_ORIPPLE = R_ESR (ΔI_L) = 0.02Ω(1.5A) = 30mV_P-P
TYPICAL APPLICATIONS
10μF
2.2Ω
35V
1μF
V_IN
10μF
+
4.5V TO 24V
22μF
35V
50V
L2
0.47μH
D1
Q1
RJK0305DPB
4.7μF
0.1μF
Q2
RJK0330DPB
100Ω
2mΩ
1000pF
V_OUT1
1.5V
15A
+
C_OUT2,3
C_OUT1
100μF
100Ω
1000pF
10k _100pF
D1, D2: VISHAY B340A
L1, L2: VISHAY IHLP4040DZERR47M11
C_OUT1, C_OUT4: TDK C322JX5R0J107MT
C_OUT2, C_OUT3, C_OUT5, C_OUT6: SANYO 4TPE 220μF
D3 _{VIN PGOOD EXTVCC INTVCC}
TG1
TG2
BOOST1
BOOST2
SW1
SW2
LTC3865
BG1
BG2
MODE/PLLIN
I_LIM
SENSE1⁺
PGND
FREQ
SENSE2⁺
RUN1
SENSE1^–
VID11
VID12
V_OSENSE1
I_TH1
TK/SS1
SGND
RUN2
SENSE2^–
VID21
VID22
V_OSENSE2
I_TH2
TK/SS2
0.1μF 0.1μF
D4
0.1μF
Q3
RJK0305DPB
Q4
RJK0330DPB
L2
0.47μH
D2
100Ω
1000pF
100Ω
1000pF
+
C_OUT5,6
162k _15k
1%
100pF
2mΩ
V_OUT2
1.2V
15A
C_OUT4
100μF
3865 F16
Figure 16. 1.5V/15A, 1.2V/15A Converter Using Sense Resistors
3865fb
33