MAX724CCK Maxim Integrated Products, MAX724CCK Datasheet - Page 12

• 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: -

The MAX724/MAX726 can convert positive input volt-
ages to negative outputs if the sum of input and output
voltage is greater than 8V, and the minimum positive
supply is 4.5V. The connection in Figure 7 shows the
MAX724 generating -5V. The device's GND pin is con-
nected to the negative output, which allows the feed-
back divider, R3, and R4 to be connected normally. If
the GND pin were tied to circuit ground, a level shift
and inversion would be required to generate the proper
feedback signal.
Component values in Figure 8 are shown for input volt-
ages up to 35V and for a 1A output. If the maximum
input voltage is lower, a Schottky diode with lower
reverse breakdown than the MBR745 (D1) may be
used. If lower output current is needed, then the cur-
rent rating of both D1 and L1 may be reduced. In addi-
tion, if the minimum input voltage is higher than 4.5V,
then greater output current can be supplied.
R1, R2, and C4 provide compensation for low input
voltages, but R1 and R2 also figure in the output-volt-
age calculation because they are effectively connected
in parallel with R3. For larger negative outputs,
increase R1, R2, and R3 proportionally while maintain-
Figure 7. Positive-to-Negative DC-DC Inverter
___________________Typical Applications
+4.5V TO +35V
D1 - MOTOROLA MBR745
C1 - NICHICON UPL1C221MRH6
V
IN
Positive-to-Negative DC-DC Inverter
0.1 F
C3
ALL RESISTORS HAVE 1% TOLERANCE
V
C
MAX724
______________________________________________________________________________________
V
IN
GND
V
C1
SW
FB
D1
220 H
50V
C2 - NICHICON UPL1A102MRH6
L1 - COILTRONICS CTX25-5-52
50 H
0.01 F
L1
5A
C4
R1
5.1k
R2
10k
Switch-Mode DC-DC Regulators
R4
1.82k
R3
2.74k
C2
1000 F
10V
-5V
1A
5A/2A Step-Down, PWM,
ing the following relationships. If V
2V
and R4 set the output voltage.
The MAX724/MAX726 can also work as a negative
boost converter (Figure 8) by tying the GND pin to the
negative output. This allows the regulator to operate
from input voltages as low as -4.5V. If the regulated
output is at least -8V, R1 and R2 set the output volt-
age as in a conventional connection, with R1 selected
from:
L1 must be a low value to maintain stability, but if V
greater than -10V, L1 can be increased to 50 H. Since
this is a boost configuration, if the input voltage
exceeds the output voltage, D1 will pull the output more
negative and out of regulation. Also, if the output is
pulled toward ground, D1 will drag down the input sup-
ply. For this reason, this configuration is not short-cir-
cuit protected.
Figure 8. Negative Step-Up DC-DC Converter
-4.5V TO -15V
OUT
-V
100 F
IN
25V
C3
, then R1, R2, and C4 can be omitted and only R3
Negative Boost DC-DC Converter
R4 = 1.82k
R3 = |V
R1 = 1.86 (R3)
R2 = 3.65 (R3)
GND
MAX724
0.01 F
R1 =
V
IN
V
V
OUT
V
C
SW
FB
750
1 F
OUT
C2
R3
2.21
| - 2.37 (in k )
R2
25 H
L1
1000pF
- R2
IN
does not fall below
MBR735
2.21k
R2
D1
12.7k
R1
1000 F
25V
C1
V
-15V
IN
OUT
11
is