SNVS555D January 2008 – December 2014 LM3881
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The Simple Power Sequencer contains three open-drain output flags which need to be pulled up for proper operation. 100-kΩ resistors can be used as pullup resistors.
See Enable Circuit.
See Adjustable Timing.
The Simple Power Sequencer is used to implement a power-up (1 - 2 - 3) and power-down (3 - 2 - 1) sequence of three power supplies.
For this design example, use the parameters listed in Table 1 as the input parameters.
|Design Parameter||Example Value|
|Input Supply voltage range||2.7 V to 5.5 V|
|Flag Output voltage, EN high||Input Supply|
|Flag Output voltage, EN low||0 V|
|Flag Timing Delay, TD1||10.8 ms - 12.0 ms|
|Flag Timing Delay, TD2 and TD3||9.6 ms|
|Power-Up Sequence||1 - 2 - 3|
|Power-Down Sequence||3 - 2 - 1|
|Ref Des||Description||Case Size||Manufacturer||Manufacturer P/N|
|U1||LM3881 Sequencer||MSOP-8||Texas Instruments||LM388|
|R1||100 kΩ||0603||Vishay Dale||CRCW06031003F-e3|
|R2||100 kΩ||0603||Vishay Dale||CRCW06031003F-e3|
|R3||100 kΩ||0603||Vishay Dale||CRCW06031003F-e3|
|CADJ||10 nF ±10% X7R 16 V||0603||Murata||GRM188R71C103KA01|
A timing capacitor of CADJ = 10 nF generates typical time delays TD2 and TD3 of 9.6 ms and TD1 of between
10.8 ms and 12.0 ms. The INV pin is tied to GND so that the output flags are active high. See Adjustable Timing for calculating the value for CADJ.
For applications requiring a flag output voltage that is different from the VCC, a separate Flag Supply may be used to pullup the open-drain outputs of the Simple Power Sequencer. This is useful when interfacing the flag outputs with inputs that require a different voltage than VCC. The designer must ensure the Flag Supply voltage is within the range specified in the Recommended Operating Conditions.