LMP8645HVMK/NOPB National Semiconductor, LMP8645HVMK/NOPB Datasheet - Page 11

• Manufacturer Part Number: LMP8645HVMK/NOPB
• Description: IC AMP CURRENT SENSE 6TSOT
• Manufacturer: National Semiconductor

Specifications of LMP8645HVMK/NOPB

• Amplifier Type: Current Sense
• Number Of Circuits: 1
• Slew Rate: 0.6 V/µs
• -3db Bandwidth: 860kHz
• Current - Input Bias: 13µA
• Voltage - Input Offset: 1700µV
• Current - Supply: 2.2mA
• Current - Output / Channel: 5mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 12 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-6, TSOT-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• Gain Bandwidth Product: -
• Other names: LMP8645HVMK

Also in this Range once selected the R
V
The max voltage at the R
V
the maximum allowable output voltage according to the Elec-
trical Tables.So all the R
previous inequality are allowed. The graphical representation
in
R
Also in this Range once selected the R
V
From the Ranges showed above a good way to maximize the
output voltage swing of the LMP8645 is to select the max al-
lowable Rgain according to the previous equations. For a
SENSE
OUT
SENSE
GAIN
helps in the selection; all the combinations (V
= V
) below the curves are allowed.
Range is fixed too.
Range is fixed too.
SENSE
FIGURE 3. Allowed Gains for Range 2
FIGURE 4. Allowed Gains for Range 3
* R
GAIN
Range 3
/R
IN
G
GAIN
≤
pin is Vout_max, it means that
Vout_max where Vout_max is
V
resistors which respect the
CM
≥
V
S
GAIN
GAIN
(Gain) the
(Gain) the
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SENSE
,
11
fixed supply voltage and Vsense as the common mode volt-
age increases, the max allowable Rgain increases too.
DESIGN GUIDELINE
Example 1
The LMP8645 is used to monitor the current supply of an ac-
tive device (Refer to
5V the active device is supplied at 12V and the max current
sunk is 1A. In this example the LMP8645 will work in all 3
Ranges: in Range 1 at the turning on of the active device, then
in Range 3 passing through the Range 2. Since the purpose
of the application is monitor the current of the active device in
any operating state working condition (power on, normal op-
eration, etc.), the gain resistor will be selected according to
the Range 1, the Range which gives more constraints to the
output dynamic voltage of the LMP8645.
At the startup of the monitored device the LMP8645 works at
0V common mode, it means that its max output is 1.3V
(Range 1). In order to maximize the resolution the Rsense is
calculated as max allowed Vsense (Refer to
by max current (1A), so Rsesne=0.5Ω. Due to the output lim-
itation the max allowed gain will be 2.6V/V so R
With this approach the current is monitored at any working
condition but without using the entire output dynamic of the
LMP8645. Alternatively if the monitored device doesn’t sink
1A at any supply voltage, it is possible to design considering
the max output voltage of the LMP8645 when operating in
Range 3 (V
the resolution using Rsesne=0.5Ω, and maximize the output
dynamic with Rgain=33kΩ. With this approach the max de-
tectable current when V
while for V
fer to
The second approach maximizes the output dynamic but im-
plies some knowledge on the monitored current.
FIGURE 5. LMP8645 in current monitor application
Figure
CM
CM
=2.5V the max detectable current is 600mA (Re-
2) and for V
≥
V
S
). Also in this case is possible to maximize
Figure
CM
CM
is less than 1,8V is about 400mA,
≥
5). The LMP8645 is supplied at
V
S
is 1A.
Figure
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GAIN
2) divided
=13kΩ.
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