Rainbow Electronics MAX16913A - Manual (Page 6)

MAX16913/MAX16913A
Remote Antenna Current-Sense
Amplifier and Switches
6 _______________________________________________________________________________________
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
amplifier that amplifies the voltage between V
IN
and
V SENS . A sense resistor (0.65Ωmin, 4.7Ωmax), R SENSE ,
is connected across V IN and V SENS . When the load
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-
cuit current (I
SC ), the device enters the short-circuit
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.
For the MAX16913, when (V
IN
- V
SENS
) drops below
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
threshold (I
SC ), the t BLANK timer begins counting.
During this period, the load current is limited to a value
of twice the short-circuit current threshold (2 x I
SC ). If
the short-circuit condition is present for t BLANK , SC
asserts low and the internal switch turns off. The timer
resets if the short-circuit condition disappears before
the blanking time (t
BLANK ) has elapsed. If the switch is
turned off at the end of t
BLANK
, a retry timer (t
RETRY
)
starts immediately after the blanking time has elapsed.
During that time, the switch stays off. At the end of
t
RETRY , the switch turns on again. If the fault still exists,
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