LTC1559CS-3.3 데이터 시트보기 (PDF) - Linear Technology

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LTC1559CS-3.3

Backup Battery Controller with Fixed Output

Linear Technology 

U

W

SWITCHING WAVEFORMS

Cold Power Boot-Up Description

1. System regulator starts to ramp up the output (PS)

once the VBAT voltage increases beyond the minimum

input value.

2. VCC starts to increase once PS is high enough to turn on

QEXT’s body diode. RESET is asserted when VCC is less

than or equal to 1V.

LTC1559-3.3/LTC1559-5

3. The LTC1559’s internal bandgap wakes up. QEXT turns

on and VCC = PS. The LTC1559’s internal boost con-

verter does not turn on as RESET remains asserted.

4. RESET is asserted for a further 200ms after VCC reaches

– 5.5% of its rated VCC value for the LTC1559-3.3 and

– 6% of its rated VCC value for the LTC1559-5.

Backup Mode (Main Battery Discharged)—

LTC1559-3.3

1.2V

VNiCd

– 7%

VCC

BOOST CONVERTER OUTPUT

–5.5%

– 7%

– 7%

1V

0.9V

tr

tf

BACKUP

INDUCTOR

CURRENT

tr

“1”

RESET

“1”

LOBAT

tr

tr

(1)

(2)

(3)

Backup Mode Description

1. Trigger into Backup Mode. Main battery fails and VCC

drops 7% below the rated value. The backup pin is

asserted after a tr delay time and the boost converter is

turned on.

2. Backup Mode. The LTC1559’s boost converter charges

and discharges the inductor with 165mA peak current.

If VCC doesn’t increase above VCC(rated value) – 7%

(due to a heavy load), the boost converter increases

peak charging current to 330mA. If VCC rises above

VCC(rated value) – 7%, the boost converter stops and

the backup pin remains asserted.

(4)

1559 SW03

3. Recovery from Backup Mode. While the boost con-

verter is running, the main battery is restored. This

causes the system regulator to increase PS above VCC.

When PS > VCC or VCC > VCC(rated value) – 5.5%, the

BACKUP pin deasserts and the boost converter finishes

its last cycle.

4. Trigger into UVLO. During backup, the 1.2V NiCd cell is

discharged and its terminal voltage falls. The LOBAT pin

is asserted to give an early warning if the cell voltage

drops below 1V. RESET is asserted when the cell

voltage drops below 0.9V and the LTC1559 enters

UVLO mode.

7

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