PCA9421 datasheet(13/66 Pages) NXP

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NXP Semiconductors

PCA9421

Power management IC for low-power microcontroller applications

1. Mode setting remains the same, but the user chooses to change one or some of the enabled output rail

voltage by programming its output voltage I2C register setting

2. Mode setting changes by setting different values on MODESEL0/MODESEL1 pins or MODE0_I2C/

MODE1_I2C bits, and it causes one or some of the output rail voltage change

In such case, the SYSRSTn signal does NOT assert when any of the enabled voltage rail output voltage is in

the middle of the transition from initial output voltage level to target level.

8.10 Watchdog timer

PCA9421 provides an on-chip watchdog timer, the duration of this watchdog can be programmed via I2C

setting.

Upon initial enable, the watchdog timer starts counting. If the watchdog timer expires before reset, an interrupt

signal is issued (WD_TIMER).

When the watchdog timer expires, the following operations are expected:

1. The SYSRSTn signal asserted (HIGH to LOW)

2. All settings for LDO1/LDO2/SW1/SW2 set to Mode 0 settings

The following events reset the watchdog timer:

1. When WD_TIMER_CLR bit is set to 3b’001 at 0Dh register

2. When the device changes the mode settings

8.11 Regulators

There are four regulators on PCA9421, which include two buck regulators and two LDOs. Table 5 shows the

outline for each regulator:

Regulator name

Output regulation voltage range

Adjustable resolution

Max output current

SW1 (Core Buck)

0.5 V to 1.5 V and a fixed 1.8 V

25 mV/step

Up to 250 mA

SW2 (System Buck)

1.5 V to 2.1 V or 2.7 V to 3.3 V

25 mV/step

Up to 500 mA

LDO1 (Always-on LDO) 1.7 V to 1.9 V

25 mV/step

Up to 1 mA

LDO2 (System LDO)

1.5 V to 2.1 V or 2.7 V to 3.3 V

25 mV/step

Up to 250 mA

Table 5. Regulator summary

For each rail, its output target voltage can be set independently in mode setting 0, 1, 2 or 3. User can also

choose to switch among any of the mode settings.

8.11.1 Enable/disable and active discharge

Enable/disable: Each rail can be enabled/disabled via I2C register setting independently in each mode setting.

Active discharge: Additionally, there is an active discharge resistor on each rail, and the user can choose to

enable/disable such feature through I2C register setting, so that when the output rail is disabled, it can quickly

discharge the output voltage to ground. In addition, the active discharge is also enabled during voltage step

down. This can be disabled by MTP bit.

If the active discharge bleeding resistor is enabled AND there is a change to the output voltage of the buck

regulators to a lower value (i.e. from 0.9 V to 0.75 V) there could be a small voltage peak of 5 % higher than

the initial voltage (for 10 µs) during the transition. If this behavior is not desired, the bleeding resistor can be

PCA9421

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 1.0 — 16 October 2023

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