MAX746 Maxim, MAX746 Datasheet - Page 16

• Manufacturer Part Number: MAX746
• Description: High-Efficiency / PWM / Step-Down / N-Channel DC-DC Controller
• Manufacturer: Maxim

or equal to the N-FET’s V
the switch is off, the voltage at EXT is pulled to GND
and the N-FET source voltage is a Schottky diode
drop below GND. However, this is not always the case
in the “in-between” mode, due to the changing duty
cycle inherent with DCM. When the device is at maxi-
mum duty cycle, EXT turns off at V
sometimes turns on again after the minimum off-time
before EXT can be pulled to GND. This results in short
spikes, which can be seen on the EXT waveform in the
Typical Operating Characteristics .
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 [phone]
© 1993 Maxim Integrated Products
High-Efficiency, PWM, Step-Down,
N-Channel DC-DC Controller
Table 3. Component Suppliers
INDUCTORS
Coiltronics
Gowanda
Sumida USA
Sumida Japan
CAPACITORS
Kemet
Matsuo
Nichicon
Sprague
Sanyo USA
Sanyo Japan
United Chemi-Con
DIODES
Motorola
Nihon USA
Nihon Japan
POWER TRANSISTORS
Harris
International Rectifier
Siliconix
RESISTORS
IRC
SUPPLIER
81-3-3837-6242
81-3-3494-7411
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
81-3-3607-511
GS
PHONE
threshold voltage. Once
GS
Printed USA
, but the switch
81-3-3607-5428
81-3-3494-7414
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
FAX
At low input/output differentials, the inductor current
cannot slew quickly enough to respond to load
changes, so the output filter capacitor must hold up the
voltage as the load transient is applied. In Figure 1a’s
circuit, for V+ = 6V, increase the output filter capacitor
to 900µF (Sprague 595D low-ESR capacitors) to obtain
a transient response less than 250mV with a load step
from 0.1A to 3A. As V+ increases, the inductor current
slews faster, so the size of the output filter capacitor can
be reduced (see Table 1).
___________________Chip Topography
SHDN
REF
TRANSISTOR COUNT: 508;
SUBSTRATE CONNECTED TO HIGH.
SS
AC Stability with Low Input/Output Differentials
is a registered trademark of Maxim Integrated Products.
FB
CC
LBI LBO GND
(2.03mm)
0.080"
AV+
OUT
CS
V+
CP
HIGH
EXT
AGND
(3.30mm)
0.130"