MAX849 MAXIM [Maxim Integrated Products], MAX849 Datasheet - Page 14

• Manufacturer Part Number: MAX849
• Description: 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters
• Manufacturer: MAXIM [Maxim Integrated Products]

Adding a timing capacitor from POK to GND generates
a power-on reset delay. The reset time constant is
determined by the pull-up resistor and timing capacitor
(Figure 11). When power is turned on, POK is low and
the capacitor is shorted. When the output voltage
reaches regulation, POK goes high and the capacitor
slowly charges to the output voltage.
The timing resistor value depends on the controller’s
RESET input leakage current. The voltage drop across
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
Figure 11. Power-On Reset Delay
Table 4. Component Selection Guide
Table 5. Component Suppliers
14
Surface Mount
Through Hole
AVX
Coilcraft
Matsuo
Motorola
Sanyo
Sumida
SUPPLIER
PRODUCTION
______________________________________________________________________________________
MAX848
MAX849
USA: 803-946-0690
USA: 847-639-6400
USA: 714-969-2491
USA: 602-303-5454
USA: 619-661-6835
Japan: 81-7-2070-6306
USA: 847-956-0666
Japan: 81-3-3607-5111
OUT
POK
Sumida CDR63B, CD73, CDR73B, CD74B series
Coilcraft DO1608, DO3308, DT3316 series
Sumida RCH654 series
800-282-4975
PHONE
Power-On Reset Delay
R
C
RESET
V
CC
INDUCTORS
803-626-3123
847-639-1469
714-960-6492
602-994-6430
619-661-1055
81-7-2070-1174
847-956-0702
81-3-3607-5144
C
FAX
the timing resistor should not exceed the difference
between the output voltage and the µC reset threshold
voltage. This resistor should be large enough to mini-
mize the shutdown current.
The MAX848/MAX849 turn on when ON1 = 1 or ON2 = 0.
The µC monitors the battery voltage and turns off the
device (forces ON1 low and ON2 high) when the bat-
tery is weak.
Due to high inductor current levels and fast switching
waveforms, which radiate noise, proper PC board lay-
out is essential. Protect sensitive analog grounds by
using a star ground configuration. Minimize ground
noise by connecting PGND, the input bypass capacitor
ground lead, and the output filter capacitor ground lead
to a single point (star ground configuration). Also, mini-
mize lead lengths to reduce stray capacitance and
trace resistance.
If an external resistor divider is used to set the output
voltage (Figure 5), the trace from FB to the resistors
must be extremely short and must be shielded from
switching signals, such as CLK, DATA, or LX.
TRANSISTOR COUNT: 2059
Matsuo 267 series
Sprague 595D series
AVX TPS series
Sanyo OS-CON series
Nichicon PL series
CAPACITORS
µC-Controlled Shutdown
Layout Considerations
Chip Information
Motorola MBR0520L
Motorola 1N5817
DIODES