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| LTC3350_15 Datasheet, PDF (42/46 Pages) Linear Technology – High Current Supercapacitor Backup Controller and System Monitor | |||
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LTC3350
Typical Applications
Application Circuit 6. 11V to 15V, 2.3A Zeta-SEPIC High Voltage Capacitor Charger with 2A Input Current Limit and 10V, 25W Backup Mode
VIN
11V TO 15V
C1
0.1µF
RPF1
158k
RPF2
VDD
20k
MN1
FDMC7660S
RSNSI
0.016Ω
C2
1µF
VIN INFET VOUTM5 VOUTSP VOUTSN OUTFET
PFI
OUTFB
DRVCC
INTVCC
PFO
CAPGD
SMBALERT
SCL
SDA
R1 R2 R3
10k 10k 10k
PFO
CAPGD
SMBALERT
SCL
SDA
BST
TGATE
VCC2P5
CAP_SLCT0
CAP_SLCT1
C5
1µF
GPI
VC
RT
ITST
CC
R5 R6
22nF 107k 10M
SGND
PGND
LTC3350
SW
BGATE
CFP
CFN
ICAP
VCAP
VCAPP5
CAP4
CAP3
CAP2
CAP1
CAPRTN
CAPFB
VOUT
10V
25W IN BACKUP
C4
0.1µF
CB
0.1µF
C6
470pF
RFBO1
768k
C3
4.7µF
RFBO2
100k
Q1
Si1555DL
CB2
4.7µF
COUT
22µF
Ã5
L1
4.7µH
MP1
Si7415DN
10µF
1Ω
10µF
L2
4.7µH
MN2
FDMC86520L
C7 +
10µF
RSNSC
0.014Ω
CAP
2200µF
35V
Ã2
RCAPTOP
255k
RCAPBOT
20k
RFBC3
604k
CFBC
820pF
RFBC1
787k
RFBC2
28k
CAP: NICHICON UHW1V222MHD 3350 TA07
L1, L2: COILCRAFT XAL4030-472ME
SET ctl_cap_scale TO 1
In a Zeta-SEPIC application there are several differences
in the monitoring features due to differences in how the
LTC3350 is configured. The capacitor voltage is measured
differently, it is no longer measured in the meas_vcap
register, but in the meas_vcap1 register. The scale factor
for meas_vcap1 must be adjusted for the resistor divider
connected to the CAP1 pin. Also in this configuration
the precision current load (ITST) for the capacitance test
cannot be used. The load on the capacitors are the external
dividers only. A capacitance measurement may still be
done. The results in the meas_cap_register will have an
LSB in Farads of:
CLSB
=
In

1â


ï£ï£¬
â5.6 â¢10â7
0.2
VCAP



ï£ï£¬
1+
RCAPTOP
RCAPBOT





RT
RL
where RL is the total resistance to ground in parallel with
the capacitor, RCAPTOP is the top divider resistor from
the capacitor to CAP1 and RCAPBOT is the bottom divider
resistor from CAP1 to ground. The above equation is for
when the ctl_cap_scale bit is set to one. ESR measurements
may be possible with large capacitors with larger ESRâs.
However, the accuracy of the ESR measurement in this
application is significantly reduced. The ESR measurement
in the meas_esr register must be scaled up by the resistor
divider ratio. The voltage at the CAP1 pin should be kept
below the VSHUNT setting.
42
For more information www.linear.com/LTC3350
3350fb
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