Rainbow Electronics MAX5085 - Manual (Page 7)

Detailed Description
The MAX5084/MAX5085 are high-voltage linear regula-
tors with a 6.5V to 65V input voltage range. The devices
guarantee 200mA output current and are available with
preset output voltages of 3.3V or 5V. Both devices can
be used to provide adjustable outputs from 2.54V to
11V by connecting a resistive divider from OUT to SET
to GND. Thermal shutdown and short-circuit protection
are provided to prevent damage during overtempera-
ture and overcurrent conditions. An output sense pin
(OUT_SENSE) provides for Kelvin sensing of the output
voltage, thereby reducing the error caused by internal
and external resistances. An enable input (EN) allows
the regulators to be turned on/off through a logic-level
voltage. Driving EN high turns on the device, while dri-
ving EN low places the device in a low-power shut-
down mode. In shutdown, the supply current reduces
to 6µA (typ). Both devices operate over the -40°C to
+125°C temperature range and are available in a 3mm
x 3mm, 6-pin TDFN package capable of dissipating
1.905W at T
A = +70°C.
Regulator
The regulator accepts an input voltage range from 6.5V
to 65V. The MAX5084/MAX5085 offer fixed-output volt-
ages of 5V and 3.3V, respectively. The output voltage is
also adjustable from 2.54V to 11V by connecting an
external resistive divider network between OUT, SET,
and GND (see R1 and R2 in Figure 2). The MAX5084/
MAX5085 automatically determine the feedback path
depending on the voltage at SET.
Enable Input (EN)
EN is a logic-level enable input, which turns the
MAX5084/MAX5085 on/off. Drive EN high to turn on the
device and drive EN low to place the device in shut-
down. When in shutdown, the MAX5084/MAX5085 typi-
cally draw 6µA of supply current. EN can withstand
voltages up to 65V, allowing EN to be connected to IN
for an always-on operation. EN has an internal 5M
Ω
resistor to GND.
Remote Sensing (OUT_SENSE)
OUT_SENSE provides for Kelvin sensing of the fixed
output voltage, thus eliminating errors due to the volt-
age drop in the trace resistance between OUT and the
load. OUT_SENSE is internally connected to OUT
through a 15
Ω resistor (Figure 1), and can be left float-
ing when remote sensing is not required. However, if
accurate output voltage regulation at the load is
required, then connect OUT_SENSE directly to the load.
Thermal Protection
When the junction temperature exceeds +160°C, an
internal thermal sensor signals the shutdown logic to
turn off the pass transistor and allows the IC to cool.
The thermal sensor turns the pass transistor on again
after the junction temperature cools by 10°C. This
results in a cycled output during continuous thermal
overload conditions. Thermal protection protects the
MAX5084/MAX5085 in the event of fault conditions. For
continuous operation, do not exceed the maximum
junction temperature rating of +150°C.
Output Short-Circuit Current Limit
The MAX5084/MAX5085 feature a 340mA current limit.
The output can be shorted to GND for an indefinite
period of time without damage to the device. During a
short circuit, the power dissipated across the pass tran-
sistor can quickly heat the device. When the die tem-
perature reaches +160°C, the MAX5084/MAX5085 shut
down and automatically restart after the die temperature
cools by 10°C. This results in a pulsed output operation.
Applications Information
Output Voltage Setting
The MAX5084/MAX5085 feature Dual Mode TM opera-
tion: they operate in either a preset output voltage
mode or an adjustable output voltage mode. Connect
SET to GND for preset output voltage operation. In pre-
set mode, internal feedback resistors set the MAX5084’s
internal linear regulator to 3.3V, and the MAX5085’s inter-
nal linear regulator to 5V. In adjustable mode, select an
output from 2.54V to 11V using a resistive divider (see
R1 and R2 in Figure 2) connected from OUT to SET to
GND. In adjustable mode, first select the resistor from
SET to GND (R2) in the 1k
Ω to 100kΩ range. The resis-
tor from OUT to SET (R1) is then calculated by:
where V
SET
= 1.251V.
Available Output Current Calculation
The MAX5084/MAX5085 provide up to 200mA of con-
tinuous output current. The input voltage extends to
65V. Package power dissipation limits the amount of
output current available for a given input/output volt-
age and ambient temperature. Figure 3 depicts the
maximum power dissipation curve for these devices.
R R x
V
V
OUT
SET
1 2 1
= −

 

MAX5084/MAX5085
65V, 200mA, Low-Quiescent-Current
Linear Regulators in TDFN
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Dual Mode is a trademark of Maxim Integrated Products, Inc.