LTC1728 データシートの表示（PDF） - Linear Technology

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LTC1728

Micropower Precision Triple Supply Monitors in 8-Lead MSOP and 5-Lead SOT-23 Packages

Linear Technology 

LTC1727/LTC1728

APPLICATIONS INFORMATION

Figure 4 contains a simple circuit for 5V systems that can’t

risk the RST output going high in the 3.1V to 4.15V range

(possibly due to very slow rise time on the 5V supply).

Diode D1 powers the LTC1728-5 while dropping ≈ 0.6V

from the VCC5 pin to the VCC3 pin. This prevents the part’s

internal override circuit from being activated. Without the

override circuit active, the RST pin stays low until VCC5

reaches VRT5 ≅ 4.675V. (See Figure 5.)

5V

0.1µF

D1

LTC1728-5

5

VCC3

4 VCC5

3

VCCA

1

RST

2

GND

R1

10k

TO SYSTEM

RESET

D1: MMBD914 OR EQUIVALENT

1727/28 F04

Figure 4. LTC1728-5 Monitoring a Single 5V

Supply. D1 Used to Avoid RST High Near 3.1V

to 4V (See Figure 3)

LTC1727-2.5/LTC1728-2.5/LTC1728-1.8/LTC1728-3.3

Override Functions

The VCCA pin, if unused, can be tied to either VCC3 or VCC25/

VCC18. This is an obvious solution since the trip points for

VCC3 and VCC25/VCC18 will always be greater than the trip

point for VCCA. Likewise, the VCC25/VCC18, if unused, can

be tied to VCC3. VCC3 must always be used. Tying VCC3 to

VCC25/VCC18 and operating off of a 2.5V/1.8V supply will

result in the continuous assertion of RST.

5

VCC5 = VCCA = 0V TO 5V

10k PULL-UP FROM RST TO VCC5

4 TA = 25°C

3

2

1

0

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

VCC5 (V)

1727/28 F05

Figure 5. RST Output Voltage

Characteristics of the Circuit in Figure 4

TYPICAL APPLICATIONS

Triple Supply Monitor (3.3V, 5V and Adjustable)

ADJUSTABLE SUPPLY

OR DC/DC FEEDBACK

DIVIDER

3.3V

5V

R1*

R2*

LTC1728-5

5

VCC3

4

VCC5

3

VCCA

2

GND

1

RST

SYSTEM RESET

1727/28 TA03

*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL

COMBINATION OF R1 AND R2 ≤ 66.5k

12

For more information www.linear.com/LTC1727

17278fd

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