MAX1760EUB-T Maxim Integrated Products, MAX1760EUB-T Datasheet - Page 9

• Manufacturer Part Number: MAX1760EUB-T
• Description: DC/DC Switching Converters 0.8A Low-Noise 1MHz Step-Up
• Manufacturer: Maxim Integrated Products

Figure 3. Connecting Resistors for External Feedback
Figure 4. Soft-Start with Maximum Switch Limit Current
The MAX1760 has an internal 1.250V ±1% reference.
Connect a 0.22µF ceramic bypass capacitor from REF
to GND within 0.2in (5mm) of the REF pin. REF can
source up to 50µA of external load current.
For a fixed 3.3V output, connect FB to GND. To set
other output voltages between 2.5V and 5.5V, connect
a resistor voltage-divider to FB from OUT to GND
(Figure 3). The input bias current into FB is <20nA,
allowing large-value divider resistors without sacrificing
accuracy. Connect the resistor voltage-divider as close
to the IC as possible, within 0.2in (5mm) of FB. Choose
R2 of 270k or less, then calculate R1 using:
0.22 F
R1
R
_______________________________________________________________________________________
C
SS
SS
Setting the Output Voltages
R2
ISET
REF
V
V
OUT
FB
MAX1760
Design Procedure
V
IN
1
= 2.4V
0.22 F
I
LIM
t
R
SS
SS
= 1.25A
=
33 F
Reference
R
470k
SS
C
SS
REF
ON
ISET
CLK/SEL
PGND GND
MAX1760
3.3 H
Step-Up DC-DC Converter
POUT
FB
OUT
LX
0.8A, Low-Noise, 1MHz,
where V
1.24V.
The ISET pin adjusts the inductor current limit and
implements soft-start. With ISET connected to REF, the
inductor current limits at 1.25A. With ISET connected to
a resistive divider set from REF to GND, the current limit
is reduced according to:
Implement soft-start by placing a resistor from ISET to
REF and a capacitor from ISET to GND. In shutdown,
ISET is discharged to GND through an on-chip 100k
resistor. At power-up, ISET is 0V and the LX current is
zero. As the capacitor voltage rises, the current
increases and the output voltage rises. The soft-start
Figure 5. Soft-Start with Reduced Switch Current Limit
R1
R2
0.22 F
R
SS2
4.7
FB
0.68 F
, the boost-regulator feedback set point, is
R1 = R2
V
FB
Setting the Switch Current Limit
= 1.24V
R
C
SS1
100 F
I
SS
(
LIM
V OUT
V FB
V
OUT
REF
ISET
-
1
)
MAX1760
1.25A
1.25V
V
ISET
R
I
LIM
SS1
t
SS
and Soft-Start
= 1.25A
=
(R
470k
SS1
II
(
R
SS2
R
SS1
)
R
C
SS2
+ R
SS
SS2
)
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