LTC2921CGN データシートの表示（PDF） - Linear Technology

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LTC2921CGN

Power Supply Tracker with Input Monitors

Linear Technology 

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OPERATIO

Electronic Circuit Breaker

Placing a resistor between the VCC and SENSE pins allows

the part to detect shorts and excessive currents on the VCC

supply. The electronic circuit breaker trips when the

voltage across the resistor is >50mV for more than 1µs. A

trip causes a fault condition which interrupts the monitor

LTC2921/LTC2922 Series

sequence, and which requires reset of the circuit breaker

latch (see Interrupting Events section). Breaker reset is

achieved by pulling V1 below the reset threshold for

>150µs after the current falls below the trip point, or by

returning from undervoltage lockout on VCC.

TI I G DIAGRA S

The timing of a typical start-up sequence for the LTC2921/

LTC2922 is shown in Figure 2. VCC exceeds the undervoltage

lockout level at time 0. All monitor inputs settle between

the 0.5V monitor threshold and the 0.7V overvoltage

threshold by time 1, then a TIMER cycle starts. The TIMER

pin reaches 1.2V at time 2, and GATE ramping begins.

When the GATE ramp completes at time 3, the automatic

remote sense switches close. Another TIMER delay

begins at time 4 and finishes at time 5, at which time PG

is activated.

VCC

SENSE

0

12

UNDERVOLTAGE

LOCKOUT LEVEL

3

VCC

VCC-50mV

45

0.7V

V1

0.5V

0.7V

V2

0.5V

0.7V

V3

0.5V

0.7V

V4

0.5V

1.2V

1.2V

TIMER

GATE

VCC

REMOTE

SENSE

SWITCH

GATE

PG

The timing of a monitor failure and subsequent regular

turn-on is shown in Figure 3. Prior to time 1, a successful

turn-on sequence had completed. At time 1, monitor V2

falls below the 0.5V reference, triggering an error. The

GATE pin, PG pin, and the remote sense switches fall at

rates determined by the pull-down currents and loading

conditions of each (times 2, 3, 4). At time 5, monitor V2

recovers, and a normal turn-on sequence begins.

VCC

SENSE

1 23 4

UNDERVOLTAGE

LOCKOUT LEVEL

V1

0.7V

V2

0.5V

V3

V4

TIMER

GATE

REMOTE

SENSE

SWITCH

GATE

PG

5

VCC

VCC-50mV

0.7V

0.5V

0.7V

0.5V

0.7V

0.5V

0.7V

0.5V

1.2V

1.2V

VCC

Figure 2. Typical Start-Up Sequence

Figure 3. Monitor Failure and Start-Up Sequence Timing

29212fa

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