I_CHARGE (Amp)

0

1

2

3

4

5

0

3

6

9

12

15

18

D002

0.1 :

0.2 :

0.5 :

1 :

I_CHARGE (A)

0

0.02

0.04

0.06

0.08

0.1

0

0.02

0.04

0.06

0.08

0.1

D003

0.1 :

0.2 :

0.5 :

1 :

Frequency (Hz)

100

1000

10000

100000

1000000

1E+7

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

D001

0

10 pF

100 pF

1 nF

10 nF

OUT

SENSE

CHARGE _ MAX

SENSE

R3

V

R

I

R

15

R1

D

= D

´

´

= D

´

18

LM7301

SNOS879I – AUGUST 1999 – REVISED MAY 2016

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Copyright © 1999–2016, Texas Instruments Incorporated

Typical Applications (continued)

Self-heating of RSENSE causing ΔRSENSE with ICHARGE_MAX flowing:

(7)

8.2.2.5 Frequency Response

Depending on the application, it may be useful to have the means to control the upper end of the circuit’s

frequency response. An example is limiting the circuit’s response to high-frequency load current spikes or

switching frequencies so that the circuit only reacts to DC or lower frequencies. Capacitor C1 in Figure 27 can be

used to accomplish just that. The original circuit has a –3-dB bandwidth close to 4.5 MHz which can be reduced

by increasing the value of C1, as shown in Figure 28.

Figure 28. Current Sense Frequency Response vs C1 Value

8.2.3 Application Curves

Figure 29 shows the transfer function of the circuit for several values of RSENSE. Notice that with 1 Ω, the output

is limited to approximately 16 V because of the additional drop across the sense resistor at higher load currents.

Figure 30 shows the low-end of the load current is more non-linear for low RSENSE values, as noted in

Selecting RSENSE due to VOS. Higher RSENSE values help with this at the expense of a higher loss and voltage

drop.

Use lower sense resistor value to avoid voltage limitation!

Figure 29. Current Sense Transfer Function for Various

RSENSE Values

Line showing linearity degradation at the lower end.

Figure 30. Low-End Transfer Function for Various RSENSE