13

LTC2901

2901is sn2901

APPLICATIO S I FOR ATIO

+

COMP1

COMP2

COMP3

COMP4

RST

WDO

CRT

CWT

V1

V2

V3

V4

WDI

GND

2

16

1

15

6

7

5

9

3.3V MONITOR

1.8V MONITOR

FEEDBACK MONITOR

COMMON RESET OUT

LOW LOAD INDICATOR

4

14

3

13

8

12

11

10

LTC2901-2

PGATE

GND

6

5

4

M1

D1

1

2

3

LTC1772

R1

28k

1%

R5

0.15

Ω

R6

10k

R3

100k

R4

80.6k

C2

47

µF

6V

1.8V

0.5A

3.3V

L1

10

µH

R2

71.5k

1%

47nF

2901 F07

C1

10

µF

10V

C3

220pF

C1: TAIYO YUDEN CERAMIC LMK325BJ106K-T

C2: SANYO POSCAP 6TPA47M

D1: MOTOROLA MBRM120T3

L1: COILTRONICS UP1B-100

M1: Si3443DV

R5: DALE 0.25W

Burst Mode is a registered trademark of Linear Technology Corporation.

Figure 7. Monitor Input, Output, Feedback Voltage and Low Load Conditions on DC/DC Controller

TYPICAL APPLICATIO S

Quad Supply Monitor with Watchdog Timer Disabled

5V, 3V, 1.8V, 12V (ADJ)

COMP2

COMP4

V2

V4

GND

CWT

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

COMP3

COMP1

V3

V1

CRT

RST

WDO

WDI

R3

2.15M

1%

SYSTEM

RESET

1.8V

3V

12V

5V

R4

100k

1%

LTC2901

2901 TA02

Because 2.5V does not exist in this application, the V2

input is tied to the V1 (3.3V) input. The feedback voltage

on the LTC1772 (0.8V typ) is monitored with the adjust-

able input (V4). The RST pin will go high 216ms

feedback voltage are above threshold. Individual input

status is available at the COMPX pins.

While the voltage monitors can detect low voltage or

shorted inputs, the watchdog circuit can be used to detect

an open circuit to the primary load. With the CWT pin

unconnected, the watchdog time-out is approximately

200

µs. At low load currents on the 1.8V supply, the

LTC1772 will go into Burst Mode

open-ciruit load, the duty cycle at the gate of M1 will drop,

and the pulse spacing will exceed the watchdog time-out

period. The WDO pin will go low indicating the low load

condition. The WDO pin will return high on the next pulse

to the gate of M1. The WDO pin will remain high if the load

is restored.