Data Sheet

Bosch Sensortec | BME280 Data sheet
14 | 55
Modifications reserved | Data subject to change without notice
Document number: BST-BME280-DS002-15
Revision_1.6_092018
3. Functional description
3.1 Block diagram
Figure 2 shows a simplified block diagram of the BME280:
Logic
Pressure
front-end
OSC NVM
Voltage
reference
Voltage
regulator
(analog &
digital)
V
DDIO
GND
I
n
t
e
r
f
a
c
e
SDI
SDO
SCK
CSB
V
DD
POR
Pressure
sensing
element
Humidity
sensing
element
Humidity
front-end
Temperature
front-end
Temperature
sensing
element
ADC
Figure 2: Block diagram of BME280
3.2 Power management
The BME280 has two distinct power supply pins
 V
DD
is the main power supply for all internal analog and digital functional blocks
 V
DDIO
is a separate power supply pin used for the supply of the digital interface
A power-on reset (POR) generator is built in; it resets the logic part and the register values after both
V
DD
and V
DDIO
reach their minimum levels. There are no limitations on slope and sequence of raising
the V
DD
and V
DDIO
levels. After powering up, the sensor settles in sleep mode (described in chapter
3.3.2).
It is prohibited to keep any interface pin (SDI, SDO, SCK or CSB) at a logical high level when V
DDIO
is
switched off. Such a configuration can permanently damage the device due an excessive current flow
through the ESD protection diodes.
If V
DDIO
is supplied, but V
DD
is not, the interface pins are kept at a high-Z level. The bus can therefore
already be used freely before the BME280 V
DD
supply is established.
Resetting the sensor is possible by cycling V
DD
level or by writing a soft reset command. Cycling the
V
DDIO
level will not cause a reset.
3.3 Sensor modes
The BME280 offers three sensor modes: sleep mode, forced mode and normal mode. These can be
selected using the mode[1:0] setting (see chapter 5.4.5). The available modes are:
 Sleep mode: no operation, all registers accessible, lowest power, selected after startup
 Forced mode: perform one measurement, store results and return to sleep mode
 Normal mode: perpetual cycling of measurements and inactive periods.