5V, Step-Down,
Current-Mode PWM DC-DC Converters
MAX730A/MAX738A/MAX744A
Table 2. Component Values and Suppliers
Production
Method
MAX730AC/MAX738AC/MAX744AC
Commercial Temp. Range
Inductors
L1 = 33µH to 100µH
Sumida (708) 956-0666
CD54-101KC (MAX730AC)
CD105-101KC
(MAX738AC/MAX744AC)
Coiltronics (407) 241-7876
CTX100 series
Capacitors
C3 = 68µF, 16V
C4 = 100µF, 6.3V
Matsuo (714) 969-2491
267 series
Sprague (603) 224-1961
595D/293D series
MAX730AE/M, MAX738AE/M, MAX744AE/M
Wide Temp. Range
Inductors
L1 = 33µH
Sumida (708) 956-0666
CD54-330N (MAX730AC)
CD105-330N
(MAX738AE/M, MAX744AE/M)
Coiltronics (407) 241-7876
CTX50 series
Capacitors
C3 = 68µF, 16V
C4 = 100µF, 6.3V
Matsuo (714) 969-2491
267 series
Sprague (603) 224-1961
595D/293D series
C3 = 150µF, 16V
C4 = 220µF, 10V
C3 = 150µF, 16V
C4 = 150µF, 16V or
390µF, 6.3V
Nichicon (708) 843-7500
PL series
Low-ESR electrolytics
Sanyo (619) 661-6322
OS-CON series
Low-ESR
organic semiconductor
(Rated from -55°C to +105°C)
Mallory (317) 273-0090
THF series
C3 = 100µF, 20V
C4 = 220µF, 10V
(Rated from -55°C to +125°C)
Surface
Mount
L1 = 33µH to 100µH
Miniature
Through-
Hole
Sumida (708) 956-0666
RCH654-101K (MAX730A)
RCH895-101K
(MAX738A/MAX744A)
L1 = 33µH
Sumida (708) 956-0666
RCH654-330M (MAX730A)
RCH895-330M
(MAX738A/MAX744A)
L1 = 100µH
Low-Cost
Through-
Hole
Maxim
MAXL001
100µH iron-power toroid
Renco (516) 586-5566
RL1284-100
C3 = 150µF, 16V
C4 = 390µF, 6.3V
Maxim
MAXC001
150µF, low-ESR
electrolytic
United Chemicon
(708) 843-7500
Printed Circuit Layouts
A good layout is essential for clean, stable operation.
The layouts and component placement diagrams given
in Figures 4, 5, 6, and 7 have been successfully tested
over a wide range of operating conditions. Note that the
1µF bypass capacitor (C2) must be positioned as close
to the V+ and GND pins as possible. Also, place the out-
put capacitor as close to the OUT and GND pins as pos-
sible. The traces connecting the input and output filter
capacitors and the catch diode must be short to mini-
mize inductance and capacitance. For this reason, avoid
using sockets, and solder the IC directly to the PC
board. Use an uninterrupted ground plane if possible.
Output-Ripple Filtering
A simple lowpass pi-filter (Figure 3) can be added to
the output to reduce output ripple to about 5mVp-p.
The cutoff frequency shown is 21kHz. Since the filter
inductor is in series with the circuit output, its resis-
tance should be minimized so the voltage drop across
it is not excessive.
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
