16/19

REV1A

Application Information (Continued)

LDO Enable / Select (Power to External Bridge Sensors)

The XR18910 includes an on-board LDO that provides a

regulated voltage that can be used to power external input

bridge sensors. Two voltage options are available, 3V and

two-wire serial interface.

When the XR18910 is powered-up, the default LDO voltage

is 3V.

When the XR18910 is active (not in sleep mode), the LDO

is always on. If the LDO voltage is not used, the LDO output

can be left floating. The LDO can either stay on or shut

down while the XR18910 is in Sleep Mode.

■

■

Set LDO to shut down while XR18910 is in Sleep Mode to

save power

■

■

Set LDO to stay on while XR18910 is in Sleep Mode to

improve wake-up time

using the register address 0x07 followed by another byte

of data to select the voltage and disable setting. Refer to

the Register List in Table 1 and the example below for more

information.

Example: The example below illustrates how to select an

LDO voltage of 2.65V and keep the LDO enabled during

Sleep Mode.

To start communication with the XR18910, repeat steps 1-3 as

shown in the Inputs and Input Selection section on page 14.

Step 4

7 6 5 4 3 2 1 0

Master sends address of register to access

0

0

0

0

0

1

1

1

LDO Settings register address

= 0x07

Step 5

9

XR18910 sends acknowledge

A

Since the LDO Settings register was accessed, the

XR18910 is expecting another byte of data from the master

to complete the command. Refer to the “Byte of Parameter”

column in the Register List (Table 1). D0 and D1 are used to

select the LDO voltage and enable/disable the LDO during

Sleep Mode. Bit 0 (D0) controls the LDO voltage (0: 3V;

1: 2.65V). Bit 1 (D1) is only applicable in Sleep Mode. Bit

1 controls whether the LDO shuts down or stays on during

sleep mode (0: Enable; 1: Disable). When the XR18910 is

active, the LDO is always on.

Step 6

7

6

5

4

3

2

1

0

Master sends code to select LDO

voltage of 2.65V and Enable LDO

during Sleep Mode

0

0

0

0

0

0

0

0

0 = Enable 1 = 2.65V

Step 7

9

XR18910 sends acknowledge

A

Step 8

0

Master sends stop condition

P

NOTES:

White Block = host to XR18910, Orange Block = XR18910 to host, Grey Block =

Notes.

Current Sense Mode (Monitoring the LDO Current)

address 0x08. When activated, the LDO current is sensed

and a proportional voltage is present at the output of the

XR18910 (ILDO = VOUT/RL). Current Sense Mode stays

active until the XR18910 receives any input select command

0x10, 0x12, 0x14, 0x15, 0x18, 0x1A, 0x1C, or 0x1E).

Current sense mode can be used to monitor the change

over time of the bridge impedance.

Sleep Mode (Analog Power Down)

0x05. When activated, the XR18910 will enter sleep mode.

During sleep mode, the analog portion of the XR18910

is disabled. All register settings are retained during sleep

mode.

During sleep mode, the nominal supply current will drop

below 70µA (with LDO on) and below 45µA (with LDO off).

During sleep mode, the master can read the value in any

register that saves a value during sleep mode. The only

SLEEP_OUT (wake up) command (0x04) and the LDO

on/off and voltage command (0x07). All other register

addresses will be ignored.

Register address 0x04 is used to return to normal operation

(exit Sleep Mode).

By default, the XR18910 is active.

XR

18910