LTC1558-5 Linear Technology, LTC1558-5 Datasheet - Page 7

• Manufacturer Part Number: LTC1558-5
• Description: Backup Battery Controller with Programmable Output
• Manufacturer: Linear Technology

Backup Mode (Main Battery Discharged)
Backup Mode Description
1. Trigger into Backup Mode. The main battery fails and
2. Backup Mode. The LTC1558’s boost converter charges
Cold Power Boot-Up Description
1. The V
2. V
SWITCHING WAVEFORMS
V
BACKUP pin is asserted after a t
LTC1558’s boost converter is turned on.
and discharges the inductor with 165mA peak current.
If V
heavy load), the boost converter increases peak charg-
ing current to 330mA. When V
(V
BACKUP pin remains asserted.
diode. V
input voltage. The system regulator wakes up and
starts ramping up the system power supply. RESET
remains asserted from V
BAK
FB
REF
INDUCTOR
CURRENT
BACKUP
FB
drops 7.5% below the LTC1558’s internal V
LOBAT
RESET
increases above the system regulator’s minimum
V
BAT
NICD
doesn’t recover above (V
V
– 7.5%), the boost converter stops but the
FB
BAK
voltage increases and turns on the Q
1.2V
U
follows V
1
– 7.5%
t
RISE
BAT
CC
by one body diode drop.
BOOST CONVERTER OUTPUT
2
= 1V.
RISE
REF
W
delay time and the
– 7.5%) (due to a
FB
– 7.5%
t
RISE
rises above
EXT
REF
3
body
. The
–6%
t
FALL
3. Recovery from Backup Mode. While the boost con-
4. Trigger into UVLO. During backup, the 1.2V NiCd cell
3. The LTC1558’s internal bandgap wakes up. The
4. RESET is asserted for a further 200ms after V
verter is running, the main battery is restored. This
causes the external MOSFET’s body diode to conduct
and V
deasserts and the boost converter finishes its last cycle.
grows weak and its terminal voltage falls. The LOBAT
pin is asserted to give an early warning when the cell
voltage drops below 1V. RESET is asserted when the
cell voltage drops below 0.9V and the LTC1558 enters
UVLO mode.
LTC1558’s internal boost converter does not turn on as
RESET remains asserted. Once V
(V
time. Q
exceeds – 6% of its rated value.
REF
– 7.5%
FB
– 6%), BACKUP is deasserted after the t
EXT
is pulled higher than (V
LTC1558-3.3/LTC1558-5
turns on and V
1V
4
BAK
t
RISE
= V
0.9V
REF
BAT
FB
t
RISE
.
– 6%). BACKUP
is greater than
1558 SW03
PHL
delay
7
CC