LTC3350
42
3350fc
For more information
www.linear.com/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
V
IN
V
DD
V
IN
11V TO 15V
INFET
MN1
FDMC7660S
L1
4.7µH
R
SNSI
0.016Ω
VOUTM5VOUTSP
LTC3350
VOUTSN OUTFET
OUTFB
PFI
C1
0.1µF
C2
1µF
R
PF1
158k
C
B
0.1µF
C
B2
4.7µF
C6
470pF
10µF
10µF
1Ω
MP1
Si7415DN
MN2
FDMC86520L
Q1
Si1555DL
C3
4.7µF
C4
0.1µF
C7
10µF
R
SNSC
0.014Ω
CAP: NICHICON UHW1V222MHD
L1, L2: COILCRAFT XAL4030-472ME
SET ctl_cap_scale TO 1
CAP
2200µF
35V
×
2
R
CAPTOP
255k
R
CAPBOT
24.3k
R
FBC1
787k
R
FBC3
604k
C
FBC
820pF
R
FBC2
28k
C
OUT
22µF
×
5
R
FBO1
768k
R
FBO2
100k
R
PF2
20k
R3
10k
C5
1µF
R6
10M
R5
107k
C
C
22nF
R2
10k
R1
10k
VCC2P5
PFO
CAPGD
SMBALERT
SCL
SDA
PFO
CAPGD
SMBALERT
SCL
SDA
V
OUT
10V
25W IN BACKUP
TGATE
SW
ICAP
CAP_SLCT0
CAP_SLCT1
VCAPP5
3350 TA07
CFP
CFN
CAP4
CAP3
CAP2
CAP1
SGND
PGND
ITST
RT
VC
GPI
DRV
CC
INTV
CC
BST
L2
4.7µH
BGATE
CAPRTN
CAPFB
+
VCAP
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:
C
LSB
=
–5.6
•
10
–7
In 1–
0.2
V
CAP
⎛
⎝⎜
⎞
⎠⎟
1
+
R
CAPTOP
R
CAPBOT
⎛
⎝⎜
⎞
⎠⎟
⎡
⎣
⎢
⎤
⎦
⎥
R
T
R
L
where R
L
is the total resistance to ground in parallel with
the capacitor, R
CAPTOP
is the top divider resistor from
the capacitor to CAP1 and R
CAPBOT
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 ESR’s.
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 V
SHUNT
setting.
The voltage at the CAP1 pin will be above the default shunt
value (2.7V) when V
CAP
is greater than 31V. In order to
continue charging to 35V, the shunts should be disabled
by setting vshunt to zero (0x0000).
