LP3972 datasheet(52/59 Pages) NSC

52 / 59 page

Application Note - LP3972 Reset Sequence

INITIAL COLD START POWER ON SEQUENCE

The Back up battery is connected to the PMU, power is

applied to the back-up battery pin, the RTC_LDO turns

on and supplies a stable output voltage to the

CC_BATT pin of the Applications processor (initiating

the power-on reset event) with nRSTO asserted from the

LP3972 to the processor.

nRSTO de-asserts after a minimum of 50 mS.

The Applications processor waits for the de-assertion of

nBATT_FLT to indicate system power (V

IN) is available.

After system power (V

IN) is applied, the LP3972 de-

asserts nBATT_FLT. Note that BOTH nRSTO and

nBATT_FLT need to be de-asserted before SYS_EN is

enabled. The sequence of the two signals is indepen-

dent of each other.

The Applications processor asserts SYS_EN, the

LP3972 enables the system high-voltage power sup-

plies. The Applications processor starts its countdown

timer set to 125 mS.

The LP3972 enables the high-voltage power supplies.

— LDO1 power for V

CC_MVT (Power for internal logic

and I/O Blocks), BG (Bandgap reference voltage),

OSC13M (13 MHz oscillator voltage) and PLL en-

abled first, followed by others if delay is on.

Countdown timer expires; the Applications processor

asserts PWR_EN to enable the low-voltage power sup-

plies. The processor starts the countdown timer set to

125 mS period.

The Applications processor asserts PWR_EN (ext. pin or

2C), the LP3972 enables the low-voltage regulators.

Countdown timer expires; If enabled power domains are

OK (I

2C read) the power up sequence continues by

enabling the processors 13 MHz oscillator and PLL’s.

10. The Applications processor begins the execution of

code.

20207622

* 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.

LP3972 Arkusz danych(PDF) 52 Page - National Semiconductor (TI)

LP3972 Arkusz danych(HTML) 52 Page - National Semiconductor (TI)

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

Arkusz danych Pobierz

Link URL