LTC1265CS datasheet(11/16 Pages) LINER

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LTC1265/LTC1265-3.3/LTC1265-5

APPLICATIONS INFORMATION

Troubleshooting Hints

Since efficiency is critical to LTC1265 applications, it is

very important to verify that the circuit is functioning

correctly in both continuous and Burst Mode operation. As

the LTC1265 is highly tolerant of poor layout, the output

voltage will still be regulated. Therefore, monitoring the

output voltage will not tell you whether you have a good or

bad layout. The waveform to monitor is the voltage on the

timing capacitor Pin 5.

In continuous mode the voltage on the CT pin is a sawtooth

with approximately 0.9VP-P swing. This voltage should

never dip below 2V as shown in Figure 6a.

Figure 6. CT Waveforms

(a) POORLY DECOUPLED LTC1265

(b) WELL DECOUPLED LTC1265

Figure 7. Inductor Waveforms

When the load currents are low (ILOAD < IBURST) Burst

Mode operation occurs. The voltage on CT pin now falls to

ground for periods of time as shown in Figure 6b. During

this time the LTC1265 is in sleep mode with quiescent

current reduced to 160

µA.

The inductor current should also be monitored. If the

circuit is poorly decoupled, the peak inductor current will

be haphazard as in Figure 7a. A well decoupled LTC1265

has a clean inductor current as in Figure 7b.

3.3V

2.4V

TIME

LTC1265 F06a

(a) CONTINUOUS MODE OPERATION

3.3V

2.4V

TIME

LTC1265 F06b

(b) Burst Mode OPERATION

SLEEP MODE

LTC1265CS Datasheet(PDF) 11 Page - Linear Technology