Datasheet

LMP8358
SNOSB09B –APRIL 2010–REVISED MARCH 2013 www.ti.com
Table 5. If all three LMP8358s need a gain of 100 with a compensation level of 010. (0000 0000 0001
0011) (continued)
After first two bytes are 0000 0000 0001 0011 0000 0000 0000 0000 0000 0000 0000 0000 The data in the register of
sent LMP8358 #1 is shifted
into the register of
After second two bytes 0000 0000 0001 0011 0000 0000 0001 0011 0000 0000 0000 0000
LMP8358 #2, the data in
are sent
the register of LMP8358
After third two bytes are 0000 0000 0001 0011 0000 0000 0001 0011 0000 0000 0001 0011
#2 is shifted into the
sent
register of LMP8358 #3.
Table 6. If LMP8358 #1 needs a gain of 20 (0000 0000 0000 0001), LMP8358 #2 needs a gain of 1000 with
a compensation level of 011 (0000 0000 0001 1110), and LMP8358 #3 needs a gain of 100 with a
compenstation level of 010 (0000 0000 0001 0011).
Register of LMP8358 #1 Register of LMP8358 #2 Register of LMP8358 #3 Notes
Power on 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 Default power on state
After first two bytes are 0000 0000 0001 0011 0000 0000 0000 0000 0000 0000 0000 0000 The data in the register of
sent LMP8358 #1 is shifted
into the register of
After second two bytes 0000 0000 0001 1110 0000 0000 0001 0011 0000 0000 0000 0000
LMP8358 #2, the data in
are sent
the register of LMP8358
After third two bytes are 0000 0000 0000 0001 0000 0000 0001 1110 0000 0000 0001 0011
#2 is shifted into the
sent
register of LMP8358 #3
LMP8358 SETTINGS
Gain (Serial, Parallel)
When the LMP8358 is in Parallel Mode the gain can be set by applying a high or low level to pins 12 (G2), 13
(G1), and 14 (G0), as shown in Table 2. The Frequency Compensation bits are automatically set as shown in
Table 2 to optimize the bandwidth. In Serial Mode the gain is determined by setting G[2:0] as shown in Table 7
and the bandwidth can be changed using the Frequency Compensation bits in the register.
Table 7. Gain Setting (Register bits 2:0)
G2 G1 G0 Gain Setting
0 0 0 10x (power-up default)
0 0 1 20x
0 1 0 50x
0 1 1 100x
1 0 0 200x
1 0 1 500x
1 1 0 1000x
1 1 1 User Defined
When G[2:0] = 000b to 110b switch S1 is closed and switch S2 is open as shown in the Block Diagram.
When G[2:0] = 111b in either serial or parallel mode switch S1 is open and S2 is closed and the LMP8358 gain
is set by external resistors as shown in Figure 53. The gain is:
GAIN = 1 + (Z1/Z2) (1)
When the gain is set by external resistors and COMP[2:0] = 1xxb, a capacitor can be used to implement a noise
reduction low pass filter. See the Filter and External Filter Capacitor (Serial) section. R1and C
FILTER
are placed
between the OUT and FB pins. R2 is placed between the FB and REFS pins.
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