MAX1765EEE+T Maxim Integrated Products, MAX1765EEE+T Datasheet - Page 16

• Manufacturer Part Number: MAX1765EEE+T
• Description: IC DC-DC CONV 800MA LN 16QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX1765EEE+T

• 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-QSOP
• Power - Output: 667mW
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

used if ISET is employed to reduce the peak inductor
current (see Setting the Switch Current Limit and Soft-
Start). For high efficiency, choose an inductor with a
high-frequency core material to reduce core losses. To
minimize radiated noise, use a toroid or shielded induc-
tor. See Table 3 for suggested components and Table
4 for a list of component suppliers.
To assist startup with input voltages below 1.1V or
when V
as a 1N5817, MBR0520L or equivalent—between LX
and POUT (Figure 2). The Schottky diode carries cur-
rent after the synchronous rectifier turns off. Thus, its
current rating only needs to be 500mA. Connect the
diode as close to the IC as possible. Do not use ordi-
nary rectifier diodes; their slow switching speeds and
long reverse-recovery times render them unacceptable.
For input voltages over 1.8V, the Schottky diode may
improve light-load efficiency.
Choose input and output filter capacitors that will ser-
vice the input and output peak currents with accept-
able voltage ripple. Choose input capacitors with
working voltage ratings over the maximum input volt-
age and output capacitors with working voltage ratings
higher than the output. A 100µF, 100mΩ, low equiva-
lent-series-resistance (ESR) tantalum output capacitor
is recommended for most applications. At the output of
the linear regulator (OUTL), use a 4.7µF ceramic
capacitor for stability at loads up to 500mA.
The input filter capacitor reduces peak currents drawn
from the input source and also reduces input switching
noise. The input voltage source impedance determines
the required size of the input capacitor. When operat-
ing directly from one or two NiMH cells placed close to
the MAX1765, use a single 33µF low-ESR input filter
capacitor.
The Sanyo POSCAP, Panasonic SP/CB, and Kemet
T510 are good low-ESR capacitors. Low-ESR tantalum
capacitors offer a good trade-off between price and
performance. Do not exceed the ripple current ratings
of tantalum capacitors. Avoid aluminum electrolytic
capacitors; their high ESR typically results in higher
output ripple voltage.
Bypass REF to GND with 0.22µF. Also, bypass OUT to
GND with a 0.68µF ceramic capacitor, and connect
OUT to POUT with a 4.7Ω resistor. Each of these com-
ponents should be placed as close to its respective IC
pins as possible, within 0.2in (5mm).
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
16
______________________________________________________________________________________
OUT
Input and Output Filter Capacitors
is set for >4V, use a Schottky diode—such
Bypass Capacitors
Output Diode
High switching frequencies and large peak currents
make PC board layout a critical part of design. Poor
design will cause excessive EMI and ground bounce,
both of which can cause instability or regulation errors
by corrupting the voltage and current feedback signals.
Power components—such as the inductor, converter
IC, filter capacitors, and output diode—should be
placed as close together as possible, and their traces
should be kept short, direct, and wide. Connect the
inductor from the battery to the LX pins as close to the
IC as possible.
Keep the voltage feedback network very close to the
IC, within 0.2in (5mm) of the FB pins. Keep noisy
traces, such as those from the LX pin, away from the
voltage feedback networks and guarded from them
using grounded copper. Refer to the MAX1765 EV kit
for a full PC board example.
The MAX1765 is ideal for use in digital cordless and
PCS phones. The PA is connected directly to the step-
up converter output for maximum voltage swing and
power efficiency (Figure 10). The internal linear regula-
tor is used for postregulation to generate low-noise
power for DSP, control, and RF circuitry. The following
equations may be used to estimate the typical available
output current under conditions other than those listed
here:
Figure 7. Feedback Connections
REGULATOR
LINEAR-
OUTPUT
R3
R4
Applications Information
OUTL
FBL
GND
Use in a Typical Wireless
MAX1765
Layout Considerations
INL
PGND
POUT
Phone Application
OUT
FB
R1
R2
STEP-UP
OUTPUT