LINEAR TECHNOLOGY LTC2912, LTC2913, LTC2914 Technical data

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Versatile Voltage Monitors Simplify Detection of Overvoltage
and Undervoltage Faults – Design Note 408

Scott Jackson

Introduction

Many modern electronic systems have strict power supply
operating ranges —requiring accurate monitoring of each
supply. Some systems must know that all supplies are
present and stable before startup and some must know
if the supplies deviate from safe operating conditions.

®

The LTC

2912, LTC2913, and LTC2914 supervisors
respectively monitor single, dual, and quad power sup­plies for undervoltage and overvoltage with tight 1.5%
threshold accuracy over temperature. All monitors in the
multiple-monitor devices share a common undervoltage
output and a common overvoltage output with a timeout
period that is adjustable or disabled. Each monitor has
input glitch rejection to ensure reliable reset operation
without false or noisy triggering.

Each part has at least two options: one with capability
to latch the overvoltage output and one with capability

5V

P0WER

SUPPLIES

3.3V

2.5V

1.8V

to externally disable both outputs. The LTC2912 has a
third option with latching capability and a non-inverted
overvoltage output. Each part has an internal 6.5V shunt
regulator allowing the device to be used in a system with
any supply level.

Basic Operation

Figure 1 shows a t ypical application for the LTC2914. Each
monitored input is compared to a 0.5V threshold. Any
channel can be confi gured to monitor both undervoltage
and overvoltage conditions using a 3-resistor divider.
When monitoring a positive voltage, the VH input of the
channel is connected to the high-side tap of the resistive
divider and triggers an undervoltage condition while the
VL input is connected to the low-side tap of the resistive
divider and triggers an overvoltage condition. When an

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.

0.1µF

02/07/408

44.2k

4.53k

27.4k1k

1k

19.6k4.53k

12.4k1k

4.53k

1k

4.53k

V

CC

VH1

VL1
VH2

LTC2914-1

VL2

REF

VH3

VL3
VH4

VL4

GND TMR

SEL

LATCH

OV

UV

C

TMR

22nF

Figure 1. Quad UV/OV Supply Monitor

SYSTEM

DN408 F01

TIMEOUT = 200ms

undervoltage condition is detected, the

⎯U⎯

V output as-

serts low.

Once all undervoltage conditions clear, the

⎯U⎯V output

remains asserted until a timeout period has elapsed.
This timeout period is set by a capacitor between the
TMR and GND pins. The timeout period can be disabled
by tying the TMR pin to V

period versus TMR capacitance. The

. Figure 2 shows the timeout

CC

⎯O⎯V output behaves

in a similar manner. On parts with latching capability,

⎯O⎯V output latches when asserted until cleared by

the
the

⎯L⎯A⎯T⎯C⎯H pin. Holding the ⎯L⎯A⎯T⎯C⎯H pin high bypasses

the overvoltage latch.

Minimum Fault Length Monitor

The LTC2912-3 can be used to detect an undervoltage
condition with a minimum duration by using the VL input

10000

(ms)

1000

UOTO

100

10

UV/OV TIMEOUT PERIOD, t

1

0.1 10 100 1000

Figure 2. Timeout Period vs Capacitance

1

TMR PIN CAPACITANCE, C

TMR

(nF)

DN408 F02

and the non-inver ted OV output. For example, an automo­bile system may need to monitor the 12V power supply
during a power up condition. During the initial cranking
of the automobile, the power supply droops. If the sup­ply droop exists for an extended period, the system may
need to disconnect various circuits from the supply for
protection or disc onnect circuit s to reduce the loa d. This
is accomplished by the circuit shown in Figure 3.

The timeout func tion of the LTC2912 typically s tarts when
a fault clears. However, because the VL input is used
in this case to monitor an undervoltage instead of an
overvolt age, the timeout function occurs at the beginning
of an undervoltage condition and the OV output remains
high until the period has elapsed. If the fault still exists

when this timeout period elapses, the OV output (

⎯F⎯A⎯U⎯L⎯T)

pulls low until the fault clears. Choosing a 0.47µF timing
capacitor produces a 4.1s timeout delay. Therefore, any
supply droop lower than 9.6V and longer than 4.1s as­serts FAULT. Figure 4 shows the resulting waveform of
a supply fault condition of 9V for 5 seconds.

Conclusion

The LTC2912, LTC2913, and LTC2914 simplify power
supply monitoring of any voltage level by offering su­perior performance and fl exibility. Only a few resistors
are needed to confi gure monitoring of multiple voltages
for both undervoltage and overvoltage conditions. The
LTC2914 offers these features in a 16-lead SSOP and
16-lead (5mm × 3mm) DFN package, the LTC2913 in a
10-lead MSOP and 10-lead (3mm × 3mm) DFN package,

TM

and the LTC2912 in a tiny 8-lead ThinSOT

and 8-lead

(3mm × 2mm) DFN package.

V

MONITOR

12V

9.6V FAULT

R

B

10k

R

A

549k

C

BYP

0.1µF

V

CC

5V

LATCH

V

CC

VH

VL

TMR

C

TMR

0.47µF

T

FAULT

LTC2912-3

UV

OV

GND

DN408 F03

= 4.1s

Figure 3. Fault Detection Circuit for a 4.1s
Undervoltage Condition

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Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone]

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R
10k

OV

FAULT

V

MONITOR

FAULT

4.1s

TMR

1s/DIV

12V

9V

5V

0V

DN408 F04

Figure 4. Fault Detection Waveform of
a 4.1s Undervoltage Condition

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call [phone], Ext. 2452

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© LINEAR TECHNOLOGY CORPORATION 2007