MAX1765EUE+ Maxim Integrated Products, MAX1765EUE+ Datasheet - Page 14

• Manufacturer Part Number: MAX1765EUE+
• Description: IC DC-DC CONV 800MA LN 16TSSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX1765EUE+

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 2.5 ~ 5.5 V
• Current - Output: 800mA
• Frequency - Switching: 1MHz
• Voltage - Input: Adj down to 0.7V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Power - Output: 1.5W
• Output Voltage: 2.5 V to 5.5 V
• Output Current: 800 mA
• Input Voltage: 0.7 V to 5.5 V
• Supply Current: 100 uA
• Switching Frequency: 1200 MHz
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

that V
when OUTL is regulated, to ensure that the linear regu-
lator is saturated. Another method to configure the
MAX1765 for true shutdown is shown in Figure 6. This
shutdown function is active high and connects to the
gate of a low-impedance PFET and ONB. The PFET
acts like a switch in this situation and disconnects the
input from the load.
The MAX1765 has an internal 1.25V, 1% reference.
Connect a 0.22µF ceramic bypass capacitor to GND
within 0.2in (5mm) of the REF pin. REF can source up
to 50µA of external load current. Typically connect ISET
to REF to give the MAX1765 full inductor current limit.
Set the output voltage between +2.5V and +5.5V by
connecting a resistor voltage-divider from OUT to FB to
GND (Figure 7). Connect the resistor voltage-divider as
close to the IC as possible, within 0.2in (5mm) of FB.
Choose R2 of 40kΩ or less, then calculate R1 using:
where V
+1.25V.
For output voltages above 4V, connect a Schottky
diode between LX and POUT to prevent voltage transi-
tion from exceeding the LX voltage rating.
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
Table 2. Operating Mode Truth Table
Dual Mode is a trademark of Maxim Integrated Products
14
Shutdown
Track
Independent Regulation
DC-DC Only
LDO Only
______________________________________________________________________________________
FBL
FB
OPERATING
= 0.5V (above the Dual Mode™ threshold)
, the boost-regulator feedback set point, is
MODE
Setting DC-DC Converter Voltage
R
1
=
R
2



V
Design Procedure
V
OUT
FB
TRACK
H
H
- 1
X
X
L
L
L
L



ONA
Reference
H
H
H
L
X
X
X
L
ONB
H
H
X
L
X
L
X
L
The LDO regulation voltage can also be set similarly to
the DC-DC converter. Connecting FBL to GND sets the
LDO output to 2.85V. To set other output voltages
between 1.25V and POUT, connect a resistor-divider
from OUTL to FBL to GND (Figure 7). Connect the
resistor voltage-divider as close to the IC as possible,
within 0.2in (5mm) of FBL. The maximum input bias cur-
rent for the FBL input is 50nA. Choose R4 of 40kΩ or
less, then calculate R3 using:
where V
+1.25V.
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 (Figure 8). In
shutdown, ISET is discharged to GND through an on-
chip 100kΩ resistor. At power-up, ISET is 0V and the
current limit is zero. As the capacitor voltage rises, the
ONL
H
H
H
L
X
X
L
L
FBL
, the linear regulator feedback set point, is
I
R
LIM
3
REGULATOR
Setting the Linear Regulator Voltage
=
LINEAR
=
OFF
OFF
ON
ON
ON
1 25
R
Setting the Switch Current
.
4



A
V
V
OUTL



FBL
R
SS
Limit and Soft-Start
CONVERTER
1
R
SS
- 1
+
DC-DC
2
R
OFF
OFF



ON
ON
ON
SS
2



REF
OFF
ON
ON
ON
ON