MAX724CCK Maxim Integrated Products, MAX724CCK Datasheet - Page 11

• Manufacturer Part Number: MAX724CCK
• Description: IC DC/DC REG PWM STP-DWN TO220-5
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck), Step-Up (Boost), Inverting, Flybackr

Specifications of MAX724CCK

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 2.5 ~ 35 V
• Current - Output: 5A
• Frequency - Switching: 100kHz
• Voltage - Input: 8 ~ 40 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: TO-220-5 (Straight Leads)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

0.2 s would be needed to provide a narrow enough
duty cycle that could control current when the output is
shorted. Since 0.6 s is too long (at 100kHz), the f
is lowered to 20kHz once FB (and hence the output)
drops below about 1.3V (see Frequency vs. V
graph in the Typical Operating Characteristics ). This
way, the MAX724/MAX726's 0.6 s minimum t
a sufficiently small duty cycle (at the reduced f
that current can still be limited.
5A/2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
Figure 5. Error-Amplifier Gain as Set by R
Figure 6. Optional LC Output Filter
10
MAIN FILTER CAP
______________________________________________________________________________________
FEEDBACK RESISTOR
90° PHASE SHIFT
A
V(DC)
= g
M
(400k ) 2000
f
FREQUENCY
POLE
L
F
= 1/[2 (400k )]C
-A
A
V(HI)
V(MID)
C
F
= g
= g
M
C
R
M
f
ZERO
and C
C
/ (2 f C
C
= 1 / (2 R
C
C
)
at V
FB
ON
TO LOAD
C
Voltage
OSC
C
C
allows
C
Pin
)
) so
OSC
A series RC network connected from V
compensates the MAX724/MAX726. Compensation
R
and C
R
gain is the product of its transconductance (approxi-
mately 5000 mhos) and an internal 400k
impedance (r
approximately 2000 mhos. R
low-frequency pole and a high-frequency zero, as
shown in Figure 5.
The MAX724/MAX726 error-amplifier design minimizes
overshoot, but precautions against overshoot should
still be exercised in sensitive applications. Worst-case
overshoot typically occurs when recovering from an
output short because V
voltage. This can be checked by simply shorting and
releasing the output.
Reduce objectional overshoot by increasing the com-
pensation resistor (to 3k
the error-amplifier output, V
the negative direction. In some cases, loop stability
may suffer with a high-value compensation resistor. An
option, then, is to add output filter capacitance, which
reduces short-circuit recovery overshoot by limiting out-
put rise time. Lowering the compensation capacitor to
below 0.05 F may also help by allowing V
ther before the output rises too far.
Though not shown in the application circuits in Figures
2, 7, and 8, additional filtering can easily be added to
reduce output ripple to levels below 2%. It is more
effective to add an LC type filter rather than additional
output capacitance alone. A small-value inductor (2 H
to 10 H) and between 47 F and 220 F of filter capaci-
tance should suffice (Figure 6). Although the inductor
does not need to be of high quality (it is not switching),
it must still be rated for the full load current.
When an LC filter is added, do not move the connection
of the feedback resistor to the LC output. It should be left
connected to the main output filter capacitor (C1 in Figure
2). If the feedback connection is moved to the LC filter
point, the added phase shift may impact stability.
C
C
values are shown in the applications circuits. R
and C
C
shape error-amplifier gain as follows: At DC,
C
have no effect, so the error-amplifier's
INT
) at V
C
. So at DC, A
C
Compensation Network
Optional Output Filters
slews down from its highest
or 4k ) at V
C
, to move more rapidly in
C
Output Overshoot
and C
V(DC)
C
C
. This allows
C
C
= g
then add a
to slew fur-
to ground
M
(r
INT
load
) =
C