MAX726ECK データシートの表示（PDF） - Maxim Integrated

部品番号

コンポーネント説明

一致するリスト

MAX726ECK

5A/2A Step-Down, PWM, Switch-Mode DC-DC Regulators

Maxim Integrated 

5A/2A Step-Down, PWM,

Switch-Mode DC-DC Regulators

___________________Typical Applications

Positive-to-Negative DC-DC Inverter

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-

ing the following relationships. If VIN does not fall below

2VOUT, then R1, R2, and C4 can be omitted and only R3

and R4 set the output voltage.

R4 = 1.82kΩ

R3 = |VOUT| - 2.37 (in kΩ)

R1 = 1.86 (R3)

R2 = 3.65 (R3)

Negative Boost DC-DC Converter

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:

R1

=

VOUT R2

2.21

-

R2

L1 must be a low value to maintain stability, but if VIN is

greater than -10V, L1 can be increased to 50µH. 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.

VIN

+4.5V TO +35V

220µH

C1 50V

VIN

VSW

MAX724

L1

50µH

5A

R1

5.1k

R2

10k

R3

2.74k

C2

1000µF

10V

FB

D1

VC

GND

C4

R4

C3

0.01µF

1.82k

0.1µF

-5V

D1 - MOTOROLA MBR745

1A

C2 - NICHICON UPL1A102MRH6

C1 - NICHICON UPL1C221MRH6

L1 - COILTRONICS CTX25-5-52

ALL RESISTORS HAVE 1% TOLERANCE

Figure 7. Positive-to-Negative DC-DC Inverter

C3

100µF

25V

-VIN

-4.5V TO -15V

VIN

FB

MAX724

VSW

GND

VC

1000pF

R1

12.7k

R2

2.21k

C1

1000µF

25V

0.01µF

C2

1µF

R3

750Ω

L1

25µH

D1

MBR735

VOUT

-15V

Figure 8. Negative Step-Up DC-DC Converter

______________________________________________________________________________________ 11

Share Link: