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LTC2915

Voltage Supervisor with 27 Selectable Thresholds

Linear Technology 

LTC2915/LTC2916

APPLICATIONS INFORMATION

Supply Monitoring

The LTC2915/LTC2916 are low voltage single supply

monitors with selectable thresholds. Two three-state inputs

select one of nine internally programmed thresholds. For

the LTC2915, a third three-state input selects the tolerance

at which the supply connected to the VM pin is monitored

(–5%, –10%, –15%). The tolerance for the LTC2916 is

fixed at –5%. Threshold accuracy is guaranteed at ±1.5%

over the entire operating temperature range.

The LTC2915/LTC2916 asserts the RST output low when

VM is below the programmed threshold, and for a reset

timeout (tRST) after VM goes above the threshold. The reset

timeout can be configured to use an internal timer with no

external components, or an adjusted timer programmed

by placing an external capacitor from RT to ground.

Power-Up

VCC powers the drive circuits for the RST pin. Therefore,

as soon as VCC reaches 0.8V during power up, the RST

output asserts low.

Until VCC reaches the undervoltage lockout threshold

(guaranteed less than 1.5V), RST is held low regardless

of the state of VM.

Once VCC is above the under voltage lockout threshold

and VM is above the programmed threshold, the reset

timer is started. After the reset timeout (tRST), the open

drain pull-down releases RST and the external pull-up

resistor pulls high.

Power-Down

On power-down, once VM drops below its threshold or

VCC drops below the undervoltage lockout, RST asserts

logic low.

Monitor Threshold Control

The monitor threshold on the VM pin is controlled by

the SEL1, SEL2 and TOL three-state pins. The SEL1 and

SEL2 pins select one of nine preset nominal voltages

(including one externally adjustable threshold) as shown

in Table 1.

The SEL1 and SEL2 three-state input pins should be con-

nected to GND, VCC or left unconnected during normal

operation. Note that when left unconnected, the maximum

leakage allowable from the pin to either GND or VCC is

±5μA.

The tolerance at which the monitored supply is measured

is set by the TOL pin (LTC2915 only), as shown in Table 2.

If desired (e.g. for margining purposes), the TOL pin may

be driven by a three-state buffer. That three-state buffer

must have a VOL and VOH which meet the VIL and VIH of

the TOL pin specified in the Electrical Characteristics, and

maintain less than 5μA of leakage in the open state.

Threshold Accuracy

The trip threshold for VM is selected by configuring the

three-state input pins. When using the adjustable input, an

external resistive divider sets the trip threshold, allowing

the user complete control over the trip point. Selection of

this trip voltage is crucial to the reliability of the system.

Table 1. Voltage Threshold Settings

NOMINAL VOLTAGE

SEL1

SEL2

12V

VCC

VCC

5V

VCC

Open

3.3V

VCC

GND

2.5V

Open

VCC

1.8V

Open

Open

1.5V*

Open

GND

1.2V*

GND

VCC

1V*

GND

Open

ADJ* (0.5V)

GND

GND

*Require a separate supply for VCC

Table 2. System Voltage Tolerance Settings

TOLERANCE

TOL

–5%

VCC

–10%

Open

–15%

GND

29156fa

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