Remote Antenna Current-Sense

Amplifier and Switches

6

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Detailed Description

The MAX16913/MAX16913A high-voltage, high-side,

current-sense switches feature internal current limiting

to prevent system damage due to fault conditions. The

MAX16913/MAX16913A input voltage range extends

from 5V to 18V, making them ideal for providing phan-

tom power to remote radio-frequency low-noise ampli-

fiers (LNAs) in automotive applications. High-side

current monitoring does not interfere with the ground

path of the load being measured, making these

devices particularly useful in a wide range of high-volt-

age battery-powered systems.

The MAX16913/MAX16913A monitor the load current

by means of a high-side current-sense amplifier and

provide an analog output voltage proportional to that

current at AOUT.

The devices combine a high-side current-sense amplifi-

er, an internal switch, a +3V bandgap reference, and

two open-drain fault indicator outputs. These features

enable the design of remote power circuits with short-

circuit, short-to-battery, and thermal protection. For the

MAX16913A, the open-load threshold is externally

adjustable using a resistive divider.

A fault-blanking feature enables the circuit to ignore

momentary faults, such as those caused by initial

charging of a capacitive load at turn-on, preventing

false alarms to the system.

The MAX16913/MAX16913A provide an active-high

control input (SHDN) to put the devices in low-power

shutdown mode.

Current-Sense Amplifier

The integrated current-sense amplifier is a differential

current passes through the sense resistor, a voltage

drop develops across it. The current-sense amplifier

amplifies this voltage.

The current-sense amplifier features an internally fixed

gain of 13V/V (typ). The following equations show the

relationship between the current-sense amplifier output

voltage (AOUT) and load current:

AOUT is the output of an internal buffer with a 5kΩ out-

put impedance.

The AOUT voltage is clamped to typically 4.3V in order

to avoid damage to external circuitry.

Load Protection

The MAX16913/MAX16913A monitor the load current

through an external sense resistor and perform the fol-

lowing actions:

•

If the monitored current is lower than the open-load

current, the device signals open load (see the

Open Load section).

•

If the monitored current is higher than the short-cir-

mode (see the

Short Circuit section).

The devices also perform a short-to-battery detection

every time the internal switch turns on (see the

Short-to-

Battery Detection section). In addition, thermal shut-

down protects the MAX16913/MAX16913A from

overheating (see the

Thermal Shutdown section). Two

open-drain outputs (

OL and SC) indicate the device

status (see Table 1).

Open Load

If the load current drops below the open-load current

threshold, the

OL output asserts low. An open-load

condition does not turn off the internal switch. The

MAX16913 provides an internally fixed open-load

threshold, while the MAX16913A features an adjustable

open-load threshold.

20mV (typ), the device signals open load.

For the MAX16913A, using a resistive divider between

REF, the open-load threshold adjustment pin (OLT),

and GND sets the open-load threshold (see the

Open-

Load Threshold Selection section).

Short Circuit

If the load current reaches the short-circuit current

During this period, the load current is limited to a value

asserts low and the internal switch turns off. The timer

resets if the short-circuit condition disappears before

starts immediately after the blanking time has elapsed.

During that time, the switch stays off. At the end of

the cycle repeats. If the fault has been removed, the

switch stays on. During this cycle,

SC stays low. During

retry when the switch is off, the current through the

I

A

(V

- V

)(V)

R

V

V

A (V/V) (V

- V

)(V) + 0.4V

LOAD

IN

SENS

SENSE

AOUT

V

IN

SENS

()

()

()

=

=×

[]

Ω