LP3972 datasheet(44/59 Pages) TI1

44 / 59 page

VCC_RTC

nRSTO

nBATT_FLT

SYS_EN

High-Volt_PD

nRESET_OUT

PWR_EN

Low-Volt_PD

13 MHZ_OSC

PXA27x Output

3,4.

9,10.

Main Batt

VIN

BU Batt

VIN

LP3972

SNVS468J – SEPTEMBER 2006 – REVISED AUGUST 2011

www.ti.com

* Note that BOTH nRSTO and nBATT_FLT need to be de-asserted before SYS_EN is enabled. The sequence of the

two signals is independent of each other and can occur is either order.

Figure 30.

POWER-ON TIMING

Symbol

Description

Min

Typ

Max

Unit

Delay from VCC_RTC assertion to nRSTO de-assertion

Delay from nBATT_FLT de-assertion to nRSTI assertion

100

µS

Delay from nRST de-assertion to SYS_EN assertion

Delay from SYS_EN assertion to PWR_EN assertion

125

Delay from PWR_EN assertion to nRSTO de-assertion

125

HARDWARE RESET SEQUENCE

Hardware reset initiates when the nRSTI signal is asserted (low). Upon assertion of nRST the processor enters

hardware reset state. The LP3972 holds the nRST low long enough (50 ms typ.) to allow the processor time to

initiate the reset state.

RESET SEQUENCE

1. nRSTI is asserted.

2. nRSTO is asserted and will de-asserts after a minimum of 50 mS

3. The Applications processor waits for the de-assertion of nBATT_FLT to indicate system power (VIN) is

available.

4. After system power (VIN) is turned on, the LP3972 de-asserts nBATT_FLT.

5. The Applications processor asserts SYS_EN, the LP3972 enables the system high-voltage power supplies.

The Applications processor starts its countdown timer.

6. The LP3972 enables the high-voltage power supplies.

7. Countdown timer expires; the Applications processor asserts PWR_EN to enable the low-voltage power

supplies. The processor starts the countdown timer.

Submit Documentation Feedback

Product Folder Links: LP3972

LP3972 Datasheet(PDF) 44 Page - Texas Instruments

LP3972 Datasheet(HTML) 44 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59

Datasheet Download

Link URL