LMH6611 Datasheet, PDF (30/42 Pages) Intersil Corporation – PowerWise® Single Supply 345 MHz Rail-to-Rail Output Amplifiers

LMH6611, LMH6612
SNOSB00K – NOVEMBER 2007 – REVISED OCTOBER 2013
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4^th ORDER MULTIPLE FEEDBACK LOW-PASS FILTER
Figure 75 shows the LMH6612 used as the amplifier in a multiple feedback low pass filter. This filter is set up to
have a gain of +1 and a −3 dB point of 1 MHz. Values can be determined by using the WEBENCH^® Active Filter
Designer found at www.ti.com/amplifiers
1.05 k:
1.02 k:
INPUT
1.05 k:
330 pF
150 pF
V⁺
62 pF
V⁺
523:
0.1 PF 1 PF
-
LMH6612
+
0.1 PF 1 PF
1.02 k:
820 pF
510:
0.1 PF 1 PF
-
LMH6612
+
0.1 PF 1 PF
V^-
V^-
Figure 75. 4^th Order Multiple Feedback Low-Pass Filter
OUTPUT
CURRENT SENSE AMPLIFIER AND OPTIMIZING ACCURACY IN PRECESION APPLICATIONS
With it’s rail-to-rail output capability, low V_OS, and low I_B the LMH6611 is an ideal choice for a current sense
amplifier application. Figure 76 shows the schematic of the LMH6611 set up in a low-side sense configuration
which provides a conversion gain of 2V/A. Voltage error due to V_OS can be calculated to be V_OS x (1 + R_F/R_G) or
1.5 mV x 21 = 31.5 mV. Voltage error due to I_O is I_O x R_F or 0.5 µA x 1 kΩ = 0.5 mV. Hence worst case total
voltage error is 12.6 mV + 0.5 mV or 13.1 mV which translates into a current error of 13.1 mV/(2 V/A) = 6.55 mA.
This circuit employs DC source resistance matching at the two input terminals in order to minimize the output DC
error caused by input bias current. Another technique to reduce output offset in a non-inverting amplifier
configuration is to introduce a DC offset current into the inverting input of the amplifier. To ensure minimal impact
on frequency response be sure to inject the DC offset current through large resistors. Conversely if optimizing an
inverting amplifier configuration simply apply offset adjustment to the non-inverting input.
0A to 1A
0.1:
+5V
51:
+
1 k: _LMH6611
-
51:
1 k:
Figure 76. Current Sense Amplifier
30
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