MAX8513 MAXIM [Maxim Integrated Products], MAX8513 Datasheet - Page 29

• Manufacturer Part Number: MAX8513
• Description: Wide-Input, High-Frequency, Triple-Output Supplies with Voltage Monitor and Power-On Reset
• Manufacturer: MAXIM [Maxim Integrated Products]

the package’s power dissipation could limit the useable
maximum input-to-output voltage differential.
The maximum power-dissipation capability of the tran-
sistor’s package and mounting must allow the actual
power dissipation in the device without exceeding the
maximum junction temperature. The power dissipated
equals the maximum load current multiplied by the
maximum input-to-output voltage differential.
When the MAX8513/MAX8514 are disabled, R26 dis-
charges C7.
The MAX8513 positive linear-regulator output voltage,
V
FB3P to GND. First, select R14 resistance value (below
1kΩ). Then, solve for R13 so:
where V
The MAX8514’s negative linear-regulator output volt-
age, V
oped through the pass transistor Q4 (MAX8514 Typical
Applications Circuits). A resistive-divider from OUT3N
to FB3N to V
Calculate V
from V
is any positive voltage (usually V
culated by:
SUP3N is the supply input for OUT3N’s transconduc-
tance amplifier. When OUT3N is used, SUP3N must be
connected to a voltage supply between 1.5V and 5.5V
that can source at least 25mA. Typically, V
used as the supply input for SUP3N.
The MAX8513/MAX8514s’ DRV3P and DRV3N outputs
are designed to drive bipolar transistors (PNP types for
the MAX8513 with the DRV3P output, and NPN types
for the MAX8514 with the DRV3N output). These bipolar
transistors form linear regulators with positive outputs
(MAX8513 from 0.8V to 27V) and negative outputs
(MAX8514 from -18V to -1V). An internal transconduc-
tance amplifier is used to drive the external pass tran-
sistors. The transconductance amplifier, pass
Wide-Input, High-Frequency, Triple-Output Supplies
OUT3P
REF3N
OUT3N
, is set with a resistive-divider from OUT3P to
OUT3P
OUT3N
, is a negative regulated voltage devel-
to FB3N to be below 5kΩ, where V
REF3N
OUT3N Voltage Selection (NPN)
OUT3P Voltage Selection (PNP)
can range from +0.8V to +27V.
R
R
13
13
______________________________________________________________________________________
by first selecting R14 the resistor
=
=
with Voltage Monitor and Power-On Reset
forces V
R
-
V
V
14
REF N
OUT N
Stability Requirements



V
3
OUT P
3
0 8
FB3N
.
OUT1
V
3
×
R
-1
to regulate to 0V.
14
). R13 is then cal-



OUT1
can be
REF3N
transistor’s specifications, the base-emitter resistor,
and the output capacitor determine the loop stability.
The total DC loop gain (A
of the internal transconductance amplifier, the gain
from base to collector of the pass transistor (Q4 in the
Typical Applications Circuits), and the gain of the feed-
back divider.
The transconductance amplifier regulates the output
voltage by controlling the pass transistor’s base cur-
rent. Its DC gain is approximately:
where G
(OUT3N), R
calculated by:
The DC gain for the transistor (Q4), including the feed-
back divider, is approximately:
V
at T
A dominant pole (f
capacitance and load resistance:
Unity-gain crossover (f
A second pole is set by the input capacitance to the
base of Q4 (C
capacitance (C
section and Figure 7), the transistor’s input resistance
(R
T
IN
f
is the thermal voltage for the transistor (typically 26mV
POLE
A
), and the base-to-emitter pullup resistor (R12):
= +27°C). The total DC loop gain for OUT3_ is:
1
=
C3_
2
A
A
IN
π
A
Q P
Q N
×
V
is typically 0.6S (OUT3P) and 0.36S
is the input resistance of Q4, and can be
4
4
C
BE
=
f
C OUT
Q4IN
OUT
G
=
_
, see the Base-Drive Noise Reduction
=
G
R
C
(
POLE1
1
IN
V
C
3
3
), any external base-to-emitter
V
V
REF N
_
3
×
REF
VT
OUT N
C_OUT3_
_
3
R
=
×
_
3
OUT
×
=
V
) is created from the output



(
3
R
) is the product of the gains
I
A
R
for OUT P or
-
OUT _
26
IN
IN
V
3
V
×
OUT N
mV
||
=
) should occur at:
||
×
3
R
2
V
R
12
REF N
π
12
3
f
POLE
β
×
)
3



)
×
C
I
3
×
OUT
A
OUT
V
1
Q
T
4
3
3
_
_
MAX
×
V
OUT
3
_
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