TPS3779DDBVR datasheet(12/28 Pages) TI1

12 / 28 page

MON(PG)

IT+

= 1 +

× V

MON(UV)

= 1 +

× V

TPS3779, TPS3780

SBVS250 – APRIL 2015

www.ti.com

9 Application and Implementation

9.1 Application Information

The TPS3779 and TPS3780 are used as precision dual-voltage detectors. The monitored voltage, VDD voltage,

and output pullup voltage (TPS3780 only) can be independent voltages or connected in any configuration.

9.1.1 Threshold Overdrive

Threshold overdrive is how much VDD exceeds the specified threshold, and is important to know because

smaller overdrive results in slower OUTx response. Threshold overdrive is calculated as a percent of the

threshold in question, as shown in Equation 1:

Overdrive = | (VDD / VIT – 1) × 100% |

where

•

VIT is either VIT– or VIT+, depending on whether calculating the overdrive for the negative-going threshold or the

positive-going threshold, respectively.

(1)

Figure 16 illustrates the VDD minimum detectable pulse versus overdrive, and is used to visualize the

relationship overdrive has on tPD(f) for negative-going events.

9.1.2 Sense Resistor Divider

The resistor divider values and target threshold voltage can be calculated by using Equation 2 and Equation 3 to

determine VMON(UV) and VMON(PG), respectively.

(2)

(3)

where

•

R1 and R2 are the resistor values for the resistor divider on the SENSEx pins,

•

VMON(UV) is the target voltage at which an undervoltage condition is detected, and

•

VMON(PG) is the target voltage at which the output goes high when VMONx rises.

Choose RTOTAL ( = R1 + R2) so that the current through the divider is approximately 100 times higher than the

input current at the SENSEx pins. The resistors can have high values to minimize current consumption as a

result of low input bias current without adding significant error to the resistive divider. For details on sizing input

resistors, refer to application report SLVA450, Optimizing Resistor Dividers at a Comparator Input, available for

download from www.ti.com.

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