Datasheet

Applications Information
Output-Voltage Selection
The MAX5087 features a Dual ModeTM operation, in
either a preset-voltage mode or an adjustable mode. In
preset-voltage mode, internal feedback resistors set the
MAX5087’s output voltage to +3.3V or +5V. Select preset-
voltage mode by connecting SET to ground. In adjustable
mode, select an output between +2.5V and +11V using
two external resistors connected as a voltage-divider to
SET (Figure 2). Set the output voltage using the following
equation:
OUT SET
R1
V V 1
R2

= ×+


where V
SET
= 1.235V and R2 is chosen to be < 100kΩ.
Available Output-Current Calculation
The MAX5087 high-voltage regulator provides up to
400mA of output current. The input voltage extends to
+45V. Package power dissipation limits the amount of out-
put current available for a given input/output voltage and
ambient temperature. Figure 3 shows the maximum power
dissipation curve for these devices. The graph assumes
that the exposed paddle of the MAX5087 package is set
up per JEDEC 51 (multilayer board) specifications.
Use Figure 3 to determine the allowable package dissi-
pation (P
D
) for a given ambient temperature. Alternately,
use the following formulas to calculate the allowable
package dissipation. Note that for the examples shown
below, the electrical characteristic limits are guaranteed
up to T
J
= +125°C (max).
A
DA
A
2.666W for T 70 C
W
P 2.666W 0.0333 (T 70 C)
C
for 70 C T 125 C
≤+ °



= − × −°

°


+ ° < ≤+ °

After determining the allowable package dissipation cal-
culate the maximum output current using the following
formula:
D
OUT(MAX)
IN OUT
P
I 400mA
VV
≅≤
−
The above equations do not include the negligible power
dissipation from self-heating due to the IC ground current.
Example 1:
T
A
= +95°C
V
IN
= +14V
V
OUT
= +5V
Find the maximum allowable output current. First cal-
culate package dissipation at the given temperature as
follows:
D
W
P 2.666W 0.0333 (95 C 70 C) 1.8335W
C
= − °− ° =
°
Then determine the maximum output current:
OUT(MAX)
(1.8335W)
I 203mA
(14V) (5V)
= =
−
Example 2:
T
A
= +125°C
V
IN
= +14V
V
OUT
= +5V
Dual Mode is a trademark of Maxim Integrated Products, Inc.
Figure 3. Calculated Maximum Power Dissipation vs.
Temperature
MAX5087 fig03
TEMPERATURE (°C)
P
D
(W)
12020 60 80 10040
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
0 140
2.666W
(16-PIN TQFN)
DERATE
33.3mW/°C
MAX5087 45V, 400mA, Low-Quiescent-Current
Linear Regulator with Adjustable Reset Delay
www.maximintegrated.com
Maxim Integrated │ 9