ML51/ML54/ML56
Sep. 01, 2020
Page
306
of 719
Rev 2.00
ML
51
/ML
54
/ML
5
6 S
E
RI
E
S
TECHNI
CA
L
RE
F
E
R
E
NC
E
M
A
NU
A
L
ML51/M
L54
/M
L56
Series
Tec
hnical Reference
Manual
Brown-Out Reset (BOR)
6.2.3.2
The other power monitoring function brown-out detection (BOD) circuit is used for monitoring the V
DD
level during execution. There are eight CONFIG selectable brown-out trigger levels available for wide
voltage applications. These eight nominal levels are 1.8V, 2.0V, 2.4V, 2.7V, 3.0V, 3.7V and 4.4V
selected via setting CBOV[2:0] (CONFIG2[6:4]). BOD level can also be changed by setting BOV[2:0]
(BODCON0[6:4]) after power-on. When V
DD
drops to the selected brown-out trigger level (V
BOD
), the
BOD logic will either reset the MCU or request a brown-out interrupt. User may decide to being reset
or generating a brown-out interrupt according to different applications. V
BOD
also can be set by
software after power-on. Note that BOD output is not available until 2~3 LIRC clocks after software
enabling.
The BOD will request the interrupt while V
DD
drops below V
BOD
while BORST (BODCON0.2) is 0. In
this case, BOF (BODCON0.3) will be set as 1. After user cleared this flag whereas V
DD
remains below
V
BOD
, BOF will not set again. BOF just acknowledge user a power drop occurs. The BOF will also be
set as 1 after V
DD
goes higher than V
BOD
to indicate a power resuming. The BOD circuit provides an
useful status indicator BOS (BODCON0.0), which is helpful to tell a brown-out event or power
resuming event occurrence. If the BORST bit is set as 1, this will enable brown-out reset function.
After a brown-out reset, BORF (BODCON0.1) will be set as 1 via hardware. It will not be altered by
reset other than power-on. This bit can be cleared by software. Note that all bits in BODCON0 is
writing protected by timed access (TA).
CBODEN
(CONFIG2.7)
CBORST
(CONFIG2.2)
V
DD
Level
BOF
1
1
> VBOD always
0
1
0
< VBOD
1
1
0
> VBOD
0
0
X
X
0
Table 6.2-3 BOF Reset Value
The ML51/ML54/ML56 Series provides low power BOD mode for saving current consumption and
remaining BOD functionality with limited detection response. By setting LPBOD[1:0] (BODCON1[2:1]),
the BOD circuit can be periodically enabled to sense the power voltage nominally every 1.6 ms, 6.4
ms, or 25.6 ms. It saves much power but also provides low-speed power voltage sensing. Note that
the hysteresis feature will disappear in low power BOD mode.
For a noise sensitive system, the ML51/ML54/ML56 Series has a BOD filter which filters the power
noise to avoid BOD event triggering unconsciously. The BOD filter is enabled by default and can be
disabled by setting BODFLT (BODCON1.0) as 0 if user requires a rapid BOD response. The minimum
brown-out detect pulse width is listed in LPBOD[1:0] (BODCON1)
Note:
Since each level of BOD voltage is selectable no matter ML51 series V
DD
range with 5.5V or
3.6V. The BOD enabled voltage value should be select base on the V
DD
.
BOV[1:0]
Brownout Detection
V
DD
+
-
V
BOD
Voltage
Select
BODEN
BOS
BORST
Brown-out Reset
BOF
Brown-out Interrupt
or
BORF
LPBOD[1:0]
BOD
Filter
BODFLT
Figure 6.2-2 Brown-out Detection Block Diagram