MAX1763EUE Maxim Integrated Products, MAX1763EUE Datasheet - Page 12

• Manufacturer Part Number: MAX1763EUE
• Description: DC/DC Switching Controllers 1.5A Low-Noise 1MHz Step-Up
• Manufacturer: Maxim Integrated Products

Specifications of MAX1763EUE

• Number Of Outputs: 1
• Output Voltage: 3.3 V
• Output Current: 1.5 A
• Input Voltage: 0.7 V to 5.5 V
• Supply Current: 2.5 mA
• Switching Frequency: 1200 MHz
• Mounting Style: SMD/SMT
• Package / Case: TSSOP-16
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C

in dropout, the MOSFET on-resistance will determine
the dropout voltage (V
lower R
tor output filter capacitance to maintain stability.
The output capacitance can be determined by the
function:
and
where V
10mS internal amplifier transconductance, G
external MOSFET transconductance, R
source resistor, and GBP is the gain-bandwidth prod-
uct of the internal gain block, 63Mrad/s.
___________________Design Procedure
For a fixed 3.3V output, connect FB to GND. To set the
output voltage between 2.5V and 5.5V, connect a resis-
tor voltage-divider to FB from OUT to GND (Figure 6).
The input bias current into FB is less than 100nA, allow-
ing 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 30kΩ or less, then calculate R1 using:
where V
1.245V.
The ISET pin adjusts the inductor peak current and can
also be used to implement soft-start. With ISET con-
nected to REF, the inductor current limits at 2.5A. 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 (>300kΩ) and a capacitor from ISET to GND. In
shutdown, ISET is discharged to GND through an inter-
nal 100kΩ resistor. As the capacitor voltage rises, the
output current is allowed to increase, and the output
voltage rises. The speed at which the output rises is
determined by the soft-start time constant:
where R
Both features may be implemented simultaneously by
placing a capacitor across the lower resistor of the cur-
rent-limiting resistive divider (Figures 7 and 8).
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
C
12
C
OUT
OUT
______________________________________________________________________________________
≥ 10
DS(ON)
≥ [ (V
SS
REF
FB
, the boost-regulator feedback set point, is
✕
≥ 300k.
is the 0.983V reference voltage, G
REF
[ (V
Setting the Switch Current Limit
I
R1 = R2((V
PFET is used, increase the linear-regula-
LIM
REF
/ V
= 2.5(V
OUT
/ [V
t
Setting the Output Voltage
SS
DROPOUT
)
OUT
= R
✕
OUT
ISET
G
SS
M
✕
/ V
GBP])
✕
C
/ 1.25) [A]
SS
= I
G
FB
FS
OUT
) - 1)
✕
✕
and Soft-Start
G
C
✕
G
M
G
R
✕
✕
is the gate-
DS(ON)
G
(R
FS
FS
G
M
✕
✕
is the
is the
). If a
2) ]
R
G
]
The MAX1763 is available in two packages, a 16-pin
QSOP and a 16-pin TSSOP-EP. Since the MAX1763
has excellent efficiency, most applications are well
served by the QSOP package. If the application
requires high power dissipation, or operation in a high
ambient temperature, choose the TSSOP-EP package.
The TSSOP-EP is equipped with an exposed metal pad
on its underside for soldering to grounded circuit board
copper. This reduces the junction-to-case thermal
Figure 6. Connecting Resistors for External Feedback
Figure 7. Soft-Start with Maximum Switch Limit Current
Figure 8. Soft-Start with Reduced Switch Limit Current
0.22µF
0.22µF
R
SS2
C
C
R
R
SS
SS
SS
SS1
REF
ISET
R1 = R2
REF
ISET
I
t
SS
LIM
= (R
= 2.5A
t
MAX1763
SS
I
LIM
MAX1763
SS1
(
MAX1763
= R
V
V
= 2.5A
(
OUT
SS
FB
R
R
SS1
SS2
C
- 1
SS
R
SS2
) C
)
+ R
Package Selection
OUT
, V
SS
FB
SS2
FB
= 1.245V, R2 ≤ 30k
)
R1
R2