LTC1559CGN-3.3 Linear Technology, LTC1559CGN-3.3 Datasheet - Page 12

• Manufacturer Part Number: LTC1559CGN-3.3
• Description: IC BACKUP BATT CNTRLR3.3V 16SSOP
• Manufacturer: Linear Technology

Specifications of LTC1559CGN-3.3

• Function: Back-Up Management
• Battery Type: Nickel Cadmium (NiCd)
• Voltage - Supply: 2.9 V ~ 3.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
LTC1559-3.3/LTC1559-5
case, the NiCd cell is assumed to be damaged and the
LTC1559’s priority is shutting down the system grace-
fully. In this case, the timer will shut off the N-channel
switch transistor after a maximum charging time (14 s).
The boost converter continues switching but delivers
reduced output power, causing V
enters UVLO if V
– 9% or if the LTC1559 detects that CTL is lower than
0.25V for two seconds, in which case “hard” reset occurs.
The discharge time can also get abnormally long if a
serious overload condition occurs during switching. The
timer shuts off the P-channel pass transistor after 10 s,
protecting the boost converter. The LTC1559 enters UVLO
as V
In addition, the LTC1559 has safe area operation protec-
tion with an internal thermal shutdown circuit. If the device
is overloaded for a long period of time, the thermal
shutdown circuit forces the LTC1559 into UVLO. The
threshold temperature for thermal shutdown is typically
155 C.
The LTC1559’s boost converter is designed so that no
current drains from the battery to the load during output
short circuit or V
system can be powered down for a long period of time.
This eliminates the risk of finding a nonfunctioning backup
system upon power-up.
Backup Cell Fast Recharge
The LTC1559 includes an onboard gas gauge circuit,
consisting of a 23-bit divider and a 9-bit up/down counter.
The gas gauge logic assumes that the boost converter
uses a 22 H inductor, allowing it to accurately measure
battery charge by counting pulses. The gas gauge counts
up from zero as charge is removed from the backup cell in
backup mode. It takes 8.4 million 165mA boost pulses
(low current mode) to increment the up/down counter by
one count. In high current mode, the 330mA pulses skip
the first two bits of the divider because each 330mA pulse
carries four times as much energy as a 165mA pulse. At
maximum load and V
gauge counter will increment by one count every 7.5 s
while the boost converter is running. Full count is reached
12
CC
drops below V
CC
= 0V conditions. This assures that the
U
CC
CC
CC
drops below V
(rated value) – 9%.
INFORMATION
= 4.625V (LTC1559-5), the gas
U
CC
to drop. The LTC1559
W
CC
(rated value)
U
after approximately 2.2 hours, equivalent to about
512mAhr of charge.
Upon entering recharge mode (after the main battery is
restored) the LTC1559 connects a 16mA fast recharge
current source from V
an internal free running oscillator counts down the gas
gauge counter at a rate designed to typically replace 160%
of the charge previously removed from the backup cell.
When the gas gauge counter reaches zero, the LTC1559
reduces the charging current at the SW pin to the user-
programmed trickle charge current level.
Under some circumstances, the LTC1559 can exit backup
mode with invalid gas gauge contents. This occurs under
three possible conditions:
1. The backup cell was completely exhausted during a
2. The backup cell was replaced while the main supply was
3. A backup cycle was terminated prematurely by a “hard”
In these cases, the LTC1559 assumes that the backup cell
is exhausted and presets the gas gauge counter to a
default capacity of 128mAhr. It then initiates a recharge
cycle.
Setting the gas gauge to this default value results in a fast
recharge cycle long enough to replenish 1.6 times
128mAhr into the backup cell (13.9 hours). If the backup
cell is actually exhausted, it will be fully recharged. If the
battery is partially or fully charged, or is significantly
smaller than 128mAhr capacity, the extra charging time is
wasted. However, the LTC1559’s 16mA fast charge cur-
rent is not high enough to damage the cell. Once the full-
count recharge has been completed, the backup cell is
assumed to be fully charged and subsequent backup/
recharge cycles resume normally.
Although the LTC1559 will not fully recharge backup cells
larger than 128mAhr capacity upon power-up, it can still
be used with such cells. Such a cell will be fully replenished
by the subsequent trickle charge cycle. Under most con-
ditions, even a partially charged large cell will still be
capable of supporting several hours of backup. For
backup cycle and the LTC1559 entered UVLO.
disabled.
reset or an output overload.
CC
to the SW pin. At the same time,