MAX1765EUE-T Maxim Integrated Products, MAX1765EUE-T Datasheet - Page 15

• Manufacturer Part Number: MAX1765EUE-T
• Description: DC/DC Switching Converters 800mA Step-Up w/500mA Linear Reg
• Manufacturer: Maxim Integrated Products

Figure 4. Dual-Output Power Supply
Figure 5. LDO Enable Allows True Boost Shutdown
OFF
ON
TRACK
0.22µF
SHDN
800mA, Low-Noise, Step-Up DC-DC Converter
0.7V TO 5.5V
OFF
ON
INPUT
ON
INPUT
TRACK
REF
ILIM
ONL
ONB
ONA
GND CLK/SEL FBL
OFF
MAX1765
3.3µH
______________________________________________________________________________________
ONL
ONA
MAX1765
R4
POUT
PGND
OUTL
OUT
FBL
INL
LX
FB
POUT
OUTL
INL
LX
R3
0.68µF
4.7µF
4.7Ω
TRACK = LOW, V
TRACK = HIGH, V
150k
50k
V
LDO
OUTPUT
with 500mA Linear Regulator
OUT
OUT
= 2.85V
= 5.0V
= 3.35V
33µF x 2
current limit increases and the output voltage rises. The
soft-start time constant is:
Placing a capacitor across the lower resistor of the cur-
rent-limiting resistive divider provides both features
simultaneously (Figure 9).
The MAX1765 is available in two packages, a 16-pin
QSOP and a thermally enhanced TSSOP-EP. The
QSOP is the less expensive of the two packages, and
requires a less complex layout design. This layout
allows the designer to route underneath the device. The
power dissipation for the QSOP is 0.7W.
The TSSOP-EP comes with an exposed metal pad that
is connected to the substrate of the IC. This increases
the power dissipation up to 1.5W for the TSSOP-EP. To
achieve maximum power capability, the exposed pad
of the TSSOP-EP should be reflowed to a pad with low
thermal resistance. For convenience, this pad can be
connected to AGND or PGND.
The MAX1765’s high switching frequency allows the
use of a small surface-mount inductor. For most appli-
cations, a 3.3µH inductor works well. The inductor
should have a saturation current rating exceeding the
N-channel switch current limit; however, it is accept-
able to bias the inductor current into saturation by as
much as 20% if a slight reduction in efficiency is
acceptable. Lower current-rated inductors may be
Figure 6. PFET Allows True Boost Shutdown
INPUT
MAX1765
t
RISE
POUT
ONB
OUT
=
LX
FB
R
SS SS
C
Package Selection
Inductor Selection
ON
SHDN
OFF
OUTPUT
15