MAX16947 Maxim, MAX16947 Datasheet - Page 17

• Manufacturer Part Number: MAX16947
• Description: The MAX16946/MAX16947 high-voltage, high-side, current-sense LDO/switches feature internal current limiting to prevent system damage due to fault conditions
• Manufacturer: Maxim

A resistive divider between REF, LIM, and GND sets the
current-limit threshold. See Figure 6.
Use the following formula to set the desired current-limit
threshold:
where I
current-sense amplifier gain (26V/V typ), and V
reference voltage (3V typ). Size R
so that the equivalent resistance of the resistive dividers
used to set the open-load and current-limit thresholds
does not exceed the REF output 100FA drive capability.
For example, to set the current-limit threshold at 120mA,
using a 0.5I sense resistor, use the following method to
calculate the value of R
Choose R
Use an external reference with resistive dividers as an
alternative means of setting the current-limit and open-
load current thresholds. The equations shown in the
Open-Load Current Threshold Selection and Current-
Limit Threshold Selection sections are still applicable
when using an external reference. In those equations,
set V
When using the devices’ 3V reference, the maximum
voltage at LIM is V
ing LIM to REF. When using an external reference, set
the voltage at LIM to no greater than V
The MAX16946 is configurable to provide a fixed 8.5V
output or as an adjustable LDO with an output between
3.3V and 15V. Connect a resistive divider between OUT,
FB, and GND to set the output to the desired voltage, as
shown in Figure 7. Connect FB to REG to configure the
MAX16946 as an 8.5V LDO, as shown in Figure 8. FB is
regulated to 1.0V with Q3% accuracy for a load current
between 5mA and 150mA. The accuracy falls to Q5% for
a load current between 2mA and 200mA. Select a value
for R
1
REF
and calculate R
CL
R
equal to the voltage of the external reference.
R
1
is the desired current-limit threshold, A
2
2
= 83kI and calculate R
=
Current-Limit Threshold Selection
=



Fixed/Adjustable Output Voltage



0.5
R
______________________________________________________________________________________
SENSE
Ω ×
LIM
Using an External Reference
0.120A 26V/V+0.4V
2
= 3V and is obtained by connect-
1
as follows:
×
and R
I
V
CL
Remote Antenna, Current-Sense and
REF
3V
R
R
×
×
1
1
2
A
:
V
1
+
and R
2
0.4V
as 156kI.
LIM(MAX)
2
−
large enough
1
−



1



REF
= 3.65V.
V
is the
is the
Select R
is negligible compared to the total current going through
R
Compensate the LDO regulator by bypassing COMP to
GND with a 0.1FF ceramic 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 0.1FF ceramic capacitor if the
input inductance (including any stray inductance) is
estimated to be 20FH. Larger capacitor values reduce
the voltage undershoot and voltage overshoot in case of
reverse current at the input.
In an analogous fashion to the input capacitor, an output
capacitor protects the device against transients due to
any series inductance in the output. Under no conditions
should the voltage on OUT go below -0.3V as specified
in the Absolute Maximum Ratings section. A Schottky
diode is required to clamp transients that go below
ground. For example, with a 2.2mH series inductance,
to avoid excessive ringing at the output, bypass OUT to
GND with not more than 0.1FF capacitance. Additionally,
bypassing OUT to GND with a 2.2FF ceramic capacitor
in series with a 10I resistor reduces ringing caused by
load current transients through a maximum 2.2mH series
inductance.
Figure 7. Adjustable Output-Voltage Selection
1
.
1
so that the maximum input bias current at FB
R
MAX16946
2
LDO/Switches
=
Compensation Capacitor



V
V
OUT
FB
R
OUT
FB
1
−
1
Output Capacitor



Input Capacitor
R
R
1
2
17