MAX1763(2001) Ver la hoja de datos (PDF) - Maxim Integrated
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MAX1763 Datasheet PDF : 16 Pages
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1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
Table 3. On/Off Logic Control
ONA
0
0
1
ONB
0
1
0
MAX1763
On
Off
On
1
1
On
TO VIN OR
VOUT
POUT
R3
MAX1763
AIN
AO
R4
R6
150k
POWER-OK
OUTPUT
Figure 3. Using the Gain Block as a Power-OK Comparator
VIN
1.8V TO 5.5V
RG
20k
VIN
2.5V
C1
COUT
1.5µH
47µF
47µF
AO
CLK/SEL LX
ONB
POUT
MBRO520L
3.3V
C4
220µF
R5
MAX1763
4.7Ω
R3
ONA
OUT
165k
C2
1µF
AIN
R4
100k
C3
0.22µF
ISET
REF
PGND
FB
GND
L1
1.5µH
C1
47µF
CLK/SEL LX
BOOST
OUTPUT
LINEAR-
REGULATED
P OUTPUT
COUT
ONA
POUT
47µF
MAX1763
R5
4.7Ω
C4
220µF
RG
20k
R3
ONB
OUT
AIN
C2
1.0µF
R4
ISET
AO
R1
REF
FB
0.22µF
PGND GND
R2
30k
SIGNAL
GROUND
POWER
GROUND
Figure 4. Using the Gain Block as a Linear Regulator from the
Boosted Output Voltage
within 0.2in (5mm) of the REF pin. REF can source up
to 50µA of external load current.
Gain Block
The MAX1763 gain block can function as a power-OK
comparator or can be used to build a linear regulator
Figure 5. Powering a Gain-Block Linear Regulator from the
Input Voltage
using an external P-channel MOSFET pass device. The
gain-block output is a single-stage transconductance
amplifier that drives an open-drain N-channel MOSFET.
The transconductance (GM) of the entire gain-block
stage is 10mS. The internal gain block amplifies the dif-
ference between AIN and the internal 0.938V reference.
To provide a power-OK signal, connect the gain-block
input, AIN, to an external resistor-divider (Figure 3). The
input bias current into AIN is less than 30nA, allowing
large-value divider resistors without sacrificing accura-
cy. Connect the resistor voltage-divider as close to the
IC as possible, within 0.2in (5mm) of AIN. Choose an
R4 value of 270kΩ or less, then calculate R3 using:
R3 = R4((VTRIP / VAIN ) - 1)
where VAIN is 0.938V.
Figures 4 and 5 show the gain block used in a linear-
regulator application. The output of an external P-chan-
nel pass element is compared to an internal 0.938V
reference. The difference is amplified and drives the
gate of the pass element. Use a logic-level PFET, such
as Fairchild’s NDS336P (RDS(ON) = 270mΩ). When the
linear-regulator output voltage is in regulation, the
MOSFET will not be full on; thus, the on-resistance will
not be important. However, if the linear regulator is used
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