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SC1545

500mA SmartLDO™ With Power Up Signal Sequencing

Semtech Corporation 

500mA SmartLDOTM With Power Up

Signal Sequencing

SC1545

PRELIMINARY - January 17, 2000

TIMING DIAGRAMS (Cont.)

After power up, there are two possible signal sequences that the device will see. The first sequence is with SLP

staying HIGH and BF_CUT transitioning from LOW to HIGH, remaining HIGH for an undetermined period and then

going back to LOW. At this point, the system state is back to where it was at the end of the power up sequence.

The sequence is shown in Figure 2 (below). During these BF_CUT transitions, the propagation delays, rise and fall

times and going into regulation times for PDR, NDR and VO are described in Electrical Characteristics on page 3.

The first sequence can start at any time after the end of the power up sequence.

Figure 2: 1st Sequence Timing

Signal sequencing for the second possible sequence is shown in Figure 3. BF_CUT goes from LOW to HIGH and

SLP goes from HIGH to LOW, 30µsec to 65µsec (T3) later. When BF_CUT goes HIGH, PDR and NDR go LOW

and the 2.5V LDO turns ON. When SLP goes LOW, PDR and NDR return to HIGH and the 2.5V LDO turns OFF.

BF_CUT will stay HIGH and SLP will stay low for an undetermined time, after which SLP will go HIGH. A minimum

of 1msec (T4) later, BF_CUT will go LOW and the system is back at the end of the power up sequence. Typical

measured values of T4 are ~250msec. During all transitions, the propagation delays, rise and fall times, and going

into regulation times for PDR, NDR and 2.5V LDO are described in Electrical Characteristics on page 3. The sec-

ond sequence can start at any time after the end of the power up sequence.

© 2000 SEMTECH CORP.

Figure 3: 2nd Sequence Timing

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