MAX16913AGEE/V(2015) Просмотр технического описания (PDF) - Maxim Integrated

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MAX16913AGEE/V
(Rev.:2015)

Remote Antenna Current-Sense Amplifier and Switches

Maxim Integrated 

MAX16913/MAX16913A

Remote Antenna Current-Sense

Amplifier and Switches

Applications Information

Choosing the Sense Resistor

REF

Ideally, the maximum load current develops the full-scale

sense voltage across the current-sense resistor. The

current-sense amplifier output voltage is given by:

MAX16913

R1

OLT

VAOUT (V) = [(VIN - VSENS)(V) x AV(V/V)] + 0.4(V)

R2

where VAOUT is the output voltage of the current-sense

amplifier, and AV is the gain of the current-sense amplifier

of 13V/V (typ). Calculate the maximum value for RSENSE

so that the differential voltage across IN and SENS does

not exceed the minimum full-scale sense voltage (87mV):

R

SENSE

(Ω)

= VDIFF(MIN)(V)

I LOAD(FULL-SCALE)(A)

where VDIFF(MIN) = VIN - VSENS = 87mV minimum at

maximum load current.

Figure 3. Open-Load Threshold Selection

where IOL is the desired open-load current threshold; AV

is the current-sense amplifier gain (13V/V typ), and VREF

is the reference voltage (+3V typ). The sum of R1 and

R2 should be large enough so that the output impedance

of the internal reference (5kΩ) is negligible compared to

the sum of R1 and R2, and has a minimum effect on the

accuracy of the adjusted open-load threshold.

Use resistors specified for current-sensing applications

with a minimum resistance value of 0.65Ω, and the

maximum resistance value of 4.7Ω. Keep inductance

For example, to set the open-load threshold at 10mA,

using a 1Ω sense resistor, use the following method to

calculate the value of R1 and R2:

lWmoweirteai-lfwfiIolSmuEnNidsSrsEeosmhisaetsowrhsaahtlaabvregetetethrh.eiLghohiwg-fhr-eienqsdutueicnntdacunycctceaonm= mceept,oawnl-ehfinlimlet. (R1R+2R(k2Ω)(k) Ω)

(= 1(Ω) ×0.01(A) ×13(V/V))+0.4V

3(V)

0.177

resistors are also available. Instead of being spiral

wrapped around a core, as in metal-film or wire-wound

resistors, they are a straight band of metal and are

available in values under 1Ω. Because of the high cur-

rent that flows through RSENSE, avoid parasitic trace

resistance from causing errors in the sense voltage.

Open-Load Threshold Selection

For the MAX16913A, a resistive divider between REF,

OLT, and GND sets the open-load threshold. See Figure 3.

Choose R1 = 470kΩ and calculate R2 as 101kΩ.

Input Capacitor

Connect a low-leakage ceramic capacitor from IN to GND

to limit the input voltage drop during momentary output

short-circuit conditions, and to protect the device against

transients due to inductance in the IN line. For example,

use at least a 0.1μF ceramic capacitor if the input

inductance (including any stray inductance) is estimated

to be 20μH. Larger capacitor values reduce the voltage

Use the following formula to set the desired open-load

threshold:

undershoot at the input.

R 2(kΩ) = (R SENSE(Ω) ×I OL(A) ×A V (V/V))+0.4V

(R1+R 2)(kΩ)

VREF(V)

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