Datasheet

At an ambient temperature of +70°C, continuous power
dissipation for the QSSOP package is 667mW, while
the TSSOP-EP can dissipate 1.5W. A first-order esti-
mate of power dissipation can be determined by calcu-
lating the output power delivered to the load (e.g., 3.3V
✕
1A = 3.3W). At the input voltage used, find the effi-
ciency from the Typical Operating Characteristics
graphs (e.g., 87%). The estimated power dissipation in
the MAX1763 is then: (100% - %Efficiency)
✕
Output
Power. The example would have: 13%
✕
3.3W = 0.43W,
allowing the QSOP package (667mW) to be used. For
higher ambient temperature, higher output power, or a
lower-efficiency operating point, the TSSOP-EP pack-
age (1.5W) may be necessary. For detailed package
mechanical information, see the package outline draw-
ings at the end of this data sheet.
Inductor Selection
The MAX1763’s high switching frequency allows the
use of a small 1.5µH surface-mount inductor. The cho-
sen inductor should generally have a saturation current
rating exceeding the N-channel switch current limit;
however, it is acceptable to bias the inductor current
into saturation by as much as 20% if a slight reduction
in efficiency is acceptable. Inductors rated for lower
peak current may be 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 ferrite core
material to reduce core losses. To minimize radiated
noise, use a toroid or shielded inductor. See Table 4 for
suggested components and Table 5 for a list of compo-
nent suppliers. Connect the inductor from the battery to
the LX pins as close to the IC as possible.
External Diode
For conditions where V
IN
might exceed the set V
OUT
, or
where V
OUT
is set above 4V, an external Schottky diode
must be connected from LX to POUT in parallel with the
on-chip synchronous rectifier. See D1 in Figure 2. The
diode should be rated for 0.5A. Representative devices
are Motorola MBR0520L, Nihon EP05Q03L, or generic
1N5817. This external diode is also recommended for
applications that must start with input voltages at or
below 1.8V. The Schottky diode carries current during
both startup and after the synchronous rectifier turns
off. Thus, its current rating only needs to be 500mA
even if the inductor current is higher. 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 circuits that do not require startup with inputs below
1.8V, and have an output of 4V or less, no external
diode is needed.
Input and Output Capacitors
Choose input and output capacitors that will service the
input and output peak currents with acceptable voltage
ripple. Choose input capacitors with working voltage rat-
ings over the maximum input voltage, and output capaci-
tors with working voltage ratings higher than the output. A
220µF, low equivalent-series-resistance (ESR) (less than
100mΩ) capacitor is recommended for most applica-
tions. Alternatively, two 100µF capacitors in parallel will
reduce the effective ESR for even better performance.
The input 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 operating
directly from one or two NiMH cells placed close to the
MAX1763, use a single 47µF low-ESR input filter capac-
itor. With higher impedance batteries, such as alkaline
and Li+, a higher value input capacitor may improve
efficiency.
Sanyo POSCAP, Panasonic SP/CB, and Kemet T510
are good low-ESR capacitors (Tables 4 and 5). Low-
ESR tantalum capacitors offer a good trade-off between
price and performance. Do not exceed the ripple cur-
rent ratings of tantalum capacitors. Avoid aluminum
electrolytic capacitors; their high ESR typically results
in higher output ripple voltage.
MAX1763
1.5A, Low-Noise, 1MHz, Step-Up
DC-DC Converter
______________________________________________________________________________________ 13
Table 5. Component Suppliers
SUPPLIER PHONE
AVX USA: 843-448-9411
Coilcraft USA: 847-639-6400
Kemet USA: 810-287-2536
Motorola
USA: 408-629-4789
Japan: 81-45-474-7030
Sumida
USA: 847-956-0666
Japan: 011-81-3-3667-3302
Note: Please indicate that you are using the MAX1763 when
contacting these component suppliers.
Table 4. Component Selection Guide
INDUCTORS CAPACITORS DIODES
AVX TPS series
Kemet T510 series
Coilcraft LPT3305
Sanyo POSCAP series
Motorola
MBR0520L
Sumida Panasonic SP/CB Nihon
EP10QY03