LTC1559-3.3/LTC1559-5
U
W U U
APPLICATIONS INFORMATION
Table 4. Button/Cylindrical NiCd 1.2V Cells
The LTC1559 works with standard or memory backup
specific NiCd cells. Memory backup cells can operate at
higher temperatures and have lower self-discharge rates.
The LTC1559’s trickle charger is designed to accommo-
date both memory backup cells (with low self-discharge)
and standard cells (with higher self-discharge). Some
recommendedmanufacturersandpartnumbersarelisted
in Table 4.
MANUFACTURER
(TYPE)
PART
NUMBER
CAPACITY
(mAhr)
R
SERIES
(Ω)
SAFT
(Memory Backup)
GB60
GB170
GB280
60
170
280
1.1
0.4
0.4
SAFT
(Standard)
VB10E
VB22E
VB30E
VB60E
100
220
300
600
0.038
0.022
0.017
0.014
The internal resistance of the backup cell increases power
dissipation as the boost converter draws current from it
during switching, degrading efficiency. Due to the fixed
inductor peak current architecture, the LTC1559’s boost
converter output power drops significantly when the NiCd
cell’s internal resistance increases at the end of its charge.
The inductor charging time increases due to a larger R/L
time constant, decreasing the switching frequency. It is
advisable, especially for batteries with high internal resis-
tance, to include a 1µF or larger bypass capacitor across
the battery to ensure that the boost converter can deliver
the maximum output power regardless of the NiCd inter-
nal resistance.
Sanyo
(Standard)
N-50AAA
N-110AA
N-120TA
N-150N
N-200AAA
N-270AA
N-500A
55
120
130
170
220
305
500
0.055
0.03
0.034
0.027
0.021
0.015
0.09
Panasonic (Standard)
P-11AA
110
0.08
15
Linear [ Linear ]
