LM3822MM-1.0/NOPB National Semiconductor, LM3822MM-1.0/NOPB Datasheet - Page 9

• Manufacturer Part Number: LM3822MM-1.0/NOPB
• Description: IC CURRENT GAUGE PREC 8-MSOP
• Manufacturer: National Semiconductor
• Type: Battery Chargerr

Specifications of LM3822MM-1.0/NOPB

• Function: Current Gauge
• Sensing Method: High-Side
• Accuracy: ±2%
• Voltage - Input: 2 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• Operating Supply Voltage (min): 2V
• Operating Supply Voltage (max): 5.25V
• Operating Temp Range: -40C to 85C
• Package Type: MSOP
• Mounting: Surface Mount
• Pin Count: 8
• Operating Temperature Classification: Industrial
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Lead Free Status / Rohs Status: Compliant
• Other names: LM3822MM-1.0; LM3822MM-1.0TR

Product Operation
The current is sampled by the delta-sigma modulator, as
illustrated in Figure 4. The pulse density output of the delta-
sigma modulator is digitally filtered. The digital output is then
compared to the output of a digital ramp generator. This
produces a PWM output. The duty cycle of the PWM output
is proportional to the amount of current flowing. A duty cycle
of 50% indicates zero current flow. If the current is flowing in
positive direction, the duty cycle will be greater than 50%.
Conversely, the duty cycle will be less than 50% for currents
flowing in the negative direction. A duty cycle of 95.5%
(4.5%) indicates the current is at I
sense currents from −I
1.0A or 2.0A. The sense current is given by:
where D is the duty cycle of the PWM waveform, and I
the full scale current (1.00A or 2.00A). Similarly, the duty
cycle is given by:
I
SENSE
MAX
= 2.2 (D−0.5)(I
to +I
MAX
MAX
. Options for I
FIGURE 4. Functional block diagram of LM3822
MAX
(−I
MAX
)
). The IC can
MAX
MAX
are
is
9
For quick reference, see the Conversion Table in Table 1.
In this IC, the current is averaged over 50 msec time slots.
Hence, momentary current surges of less than 50 msec are
tolerated.
This is a sampled data system which requires an anti-
aliasing filter, provided by the filter capacitor.
The delta-sigma modulator converts the sensed current to
the digital domain. This allows digital filtering, and provides
immunity to current and noise spikes. This type of filtering
would be difficult or impossible to accomplish on an IC with
analog components.
The user also needs to specify the full scale value. See the
Ordering Information table for details.
D = [I
SENSE
10124910
/(2.2 I
MAX
)] + 0.5
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