Datasheet

Applications Information
Available Output Current Calculation
The MAX5091 high-voltage regulator provides up to
100mA of output current. The input voltage extends to
+28V. Package power dissipation limits the amount of
output current available for a given input/output voltage
and ambient temperature. Figure 2 depicts the maximum
power dissipation curve for the 8-pin SO-EP package.
The graph assumes that the exposed metal back of the
MAX5091 package is soldered to copper on a single layer
PCB according to the JEDEC51 standard.
Use Figure 2 to determine the allowable package dissi-
pation for a given ambient temperature. Alternately, use
the following formula to calculate the allowable package
dissipation:
A
D
AA
1.538W for T 70 C
P
1.538 0.01923 (T 70 C) For 70 C T 125 C
≤+ °

=

− − ° + ° < ≤+ °

After determining the allowable package dissipation,
calculate the maximum output current using the following
formula:
D
OUT(MAX)
S OUT
P
I
VV
≅
−
The above equations do not include the power dissipation
from self-heating due to the IC ground current.
The junction-to-ambient thermal impedance depends
on the area of the copper plane, its thickness, and the
number of copper layers on PCB. For the higher power
dissipation requirement, use multiple-layered PCBs with
2oz copper and a large copper area.
Capacitor Selection and Regulator Stability
For stable operation over the full temperature range
and with load currents up to 100mA, use a 10μF output
capacitor with a low ESR. Table 1 shows a list of recom-
mended output capacitor ESR for various load conditions.
Figure 2. 8-Pin SO-EP Maximum Power Dissipation vs.
Temperature
Table 1. Recommended Output Capacitor
ESR
RECOMMENDED C
OUT
ESR
I
OUT
V
OUT
= 3.3V V
OUT
= 5.0V
I
OUT
≤ 10mA C
ESR
< 0.66Ω C
ESR
< 1Ω
I
OUT
≤ 50mA C
ESR
< 0.132Ω C
ESR
< 0.2Ω
I
OUT
≤ 100mA C
ESR
< 66mΩ C
ESR
< 0.1Ω
MAX5091 fig02
TEMPERATURE (°C)
P
D
(W)
130
120100
11030
40
50
60
70
80
9010
20
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0
140
150
1.538W
DERATE
19.23mW/°C
8-PIN SO-EP
MAX5091 28V, 100mA, Low-Quiescent-Current LDO
with Reset and Power-Fail Input/Output
www.maximintegrated.com
Maxim Integrated │ 11