LTC1558-5 Просмотр технического описания (PDF) - Linear Technology

Номер в каталоге

Компоненты Описание

производитель

LTC1558-5

Backup Battery Controller with Programmable Output

Linear Technology 

U

W

SWITCHING WAVEFORMS

Cold Power Boot-Up Description

1. The VBAT voltage increases and turns on the QEXT body

diode. VBAK follows VBAT by one body diode drop.

2. VBAK increases above the system regulator’s minimum

input voltage. The system regulator wakes up and

starts ramping up the system power supply. RESET

remains asserted from VCC = 1V.

LTC1558-3.3/LTC1558-5

3. The LTC1558’s internal bandgap wakes up. The

LTC1558’s internal boost converter does not turn on as

RESET remains asserted. Once VFB is greater than

(VREF – 6%), BACKUP is deasserted after the tPHL delay

time. QEXT turns on and VBAK = VBAT.

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

exceeds – 6% of its rated value.

Backup Mode (Main Battery Discharged)

1.2V

VNICD

BOOST CONVERTER OUTPUT

– 6%

– 7.5%

VFB

– 7.5%

– 7.5%

1V

0.9V

BACKUP

tRISE

tFALL

INDUCTOR

CURRENT

tRISE

tRISE

RESET

LOBAT

tRISE

1

2

3

Backup Mode Description

1. Trigger into Backup Mode. The main battery fails and

VFB drops 7.5% below the LTC1558’s internal VREF. The

BACKUP pin is asserted after a tRISE delay time and the

LTC1558’s boost converter is turned on.

2. Backup Mode. The LTC1558’s boost converter charges

and discharges the inductor with 165mA peak current.

If VFB doesn’t recover above (VREF – 7.5%) (due to a

heavy load), the boost converter increases peak charg-

ing current to 330mA. When VFB rises above

(VREF – 7.5%), the boost converter stops but the

BACKUP pin remains asserted.

4

1558 SW03

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

verter is running, the main battery is restored. This

causes the external MOSFET’s body diode to conduct

and VFB is pulled higher than (VREF – 6%). BACKUP

deasserts and the boost converter finishes its last cycle.

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

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.

7

Share Link: