LMP8358 datasheet(23/32 Pages) NSC

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Frequency Compensation (Serial)

The gain-bandwidth compensation is set to one of five levels

under program control. The amount of compensation can be

decreased to maximize the available bandwidth as the gain

of the amplifier is increased. The compensation level is se-

lected by setting bits COMP[2:0] of the control register with

000b, 001b, 010b, 011b, or 1xxb. Table 8. Frequency Com-

pensation (Register bits 5:3) shows the bandwidths achieved

at the selectable gain and compensation settings. Note that

for gains 10X and 20X, the recommended compensation set-

ting is 000b. For the gain setting 50X, compensation settings

may be 000b and 001b. Gain settings 100X and 200X may

use the three bandwidth compensation settings 000b, 001b,

and 010b. At gains of 500X and 1000X, all bandwidth com-

pensation ranges may be used. Note that for lower gains, it is

possible to under compensate the amplifier into instability.

Table 8. Frequency Compensation (Register bits 5:3)

Bandwidth

Gain\COMP [2:0]

000

001

010

011

1xx

930 kHz

n/a

74 kHz

385 kHz

n/a

37 kHz

160 kHz

460 kHz

n/a

16 kHz

100

80 kHz

225 kHz

640 kHz

n/a

8 kHz

200

38 kHz

95 kHz

195 kHz

n/a

4 kHz

500

16 kHz

40 kHz

85 kHz

130 kHz

1.5 kHz

1000

8 kHz

22 kHz

50 kHz

89 kHz

0.8 kHz

User Defined Gain

GBW Product

> 10x

8 MHz

> 30x

24 MHz

> 100x

80 MHz

> 300x

240 MHz

> 1x

0.8 MHz

(For external filter cap)

Input Multiplexer and Polarity Switch (Serial)

The Input Multiplexer Selection bits MUX[1:0] and Polarity bit

POL can be used to set the inputs of the LMP8358 to the

states shown in Table 9. Input Multiplexer and Polarity (Reg-

ister bits 8:6).

Table 9. Input Multiplexer and Polarity (Register bits 8:6)

MUX1

MUX0

Diff Input for POL = 0

Diff Input for POL = 1

Polarity Reversal

When MUX[1:0] = 00b and POL = 0b the LMP8358 has the

input of a normal instrumentation amplifier. The input for the

LMP8358 is defined as Gain × (V

+IN − V−IN). When POL = 1b,

the input for the LMP8358 is defined as Gain × (V

−IN – V+IN).

Polarity reversal can be used to do system level calibration,

for example, to compensate for thermocouple voltages, resid-

ual offset of the LMP8358, or offsets of the sensor or ADC.

Short Inputs

When MUX[1:0] = 01b and POL = 0b both inputs are con-

nected to the +IN pin of the LMP8358. The –IN pin is left

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