MIC2755BMM TR Micrel Inc, MIC2755BMM TR Datasheet - Page 6

• Manufacturer Part Number: MIC2755BMM TR
• Description: IC SUPERVISOR BATT SYSTEM 8-MSOP
• Manufacturer: Micrel Inc
• Type: Battery Backup Circuitr

Specifications of MIC2755BMM TR

• Number Of Voltages Monitored: 1
• Output: Open Drain or Open Collector
• Reset: Active Low
• Reset Timeout: 700 ms Minimum
• Voltage - Threshold: Adjustable/Selectable
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: MIC2755BMMTR; MIC2755BMMTR

MIC2755
Applications Information
Outputs
Since the MIC2755 outputs are open-drain MOSFETs, most
applications will require pull-up resistors. The value of the
resistors should not be too large or leakage effects may
dominate.
Programming Thresholds
There are separate resistive-divider configurations for circuits
that require or do not require manual reset capability.
Configuration Without Manual Reset
See Figure 1. The battery-OK threshold is calculated us-
ing:
The low-battery threshold is calculated using:
The dead-battery threshold is calculated using:
where, for all equations:
In order to provide the additional criteria needed to solve for
the resistor values, the resistors can be selected such that
they have a given total value, that is, R1 + R2 + R3 + R4 =
R
because it draws minimum battery current per resistor ladder
but has no significant effect on system accuracy.
When working with large resistors, a small amount of leak-
age current can cause voltage offsets that degrade system
accuracy. The maximum recommended total resistance from
V
Once the desired trip points are determined, set the V
threshold first.
For a typical single-cell lithium ion battery, 3.6V is a reason-
able “OK threshold” because at 3.6V the battery is moderately
charged. Solving for R4:
MIC2755
BAT
total
Figure 1. Example Circuit without Manual Reset
. A value such as 1MΩ for R
to ground is 3MΩ.
V
V
V
V
V
R4 = 344kΩ
V
55.6k
572k
344k
BAT(OK)
BAT(low)
BAT(dead)
BAT
REF
BAT(OK)
28k
R1
R2
R3
R4
= 1.24V
=
=
=
=
3.6V
V
V
REF
REF
V
REF
VDD
PTH
NTH
RTH(/MR)
=






R1 R2 R3 R4
R1 R2 R3 R4



1.24V
MIC2755
R1 R2 R3 R4
+
+
R2 R3 R4
+
R3 R4
/POF
/RST
GND
/NMI



+
R
1M
+
+
+
100k
4
R
+
total
4
Ω
+
+
100k 100k
+



is a reasonable value
+









V
BAT
POF
NMI
RST
BAT(OK)
6
To determine the resistor values for V
R4 = 344kΩ and solve for R3.
Once R3 and R4 are determined, the equation for V
can be used to determine R2. A single lithium-ion cell should
not be discharged below 2.5V. Many applications limit the
drain to 2.9V. Using 2.9V for the V
calculating the following resistor values.
Configuration With Manual Reset
See Figure 2. To use manual reset, the MIC2755 requires
a separate resistor ladder for the switch and fresh-battery
threshold. The remaining two thresholds are set by the three-
resistor ladder.
where, for all equations:
Once the desired trip points are determined, set R6 + R7 =
1MΩ and solve for R7.
The remaining resistor values are solved in a similar manner
as the above.
SW
Figure 2. Example Circuit with Manual Reset
V
R3 = 56k
R2 = 27.4k
R1 = 1MΩ – R2 – R3 – R4 = 572k
V
V
V
V
R7 = 344k
R6 = 1MΩ – 344k = 656k
1MΩ = R8 + R9 + R10
V
V
V
V
BAT(low)
656k
344k
BAT(OK)
BAT(low)
BAT(dead)
BAT(dead)
BAT(fresh)
BAT(low)
BAT
REF
R6
R7
= 1.24V
26.7k
573k
400k
R10
= 3.1V = 1.24V
= V
= V
= 3.1V = 1.24V
R8
R9
= V
= 2.9V = 1.24V
= 3.6V = 1.24V
REF
REF
REF






R6 R7
R8 +R9 +R10



R8 +R9 +R10
R7
VDD
PTH
NTH
RTH(/MR)
+
R9 + R10
R10
MIC2755






R +R4
1M









R10
1M
R2 + 55.6k + 344k
1M
3
BAT(dead)
R7
/POF
/RST
GND
Ω
/NMI
Ω
Ω



100k



BAT(low)



1M






100k 100k
Ω
threshold allows
January 2006
threshold, set
Micrel, Inc.



BAT(dead)
V
BAT
POF
NMI
RST