BQ76PL536PAP datasheet(21/58 Pages) TI

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REG50

RTH

REG50

TS+

TS–

IO_CTRL [TSn

]

ALERT[OTn]

PINBOUNDARY

ToADCMux

–

DelayFilter

COMPARATOR

CONFIG_OT[] Selector

CONFIG

_OTT[]

CONFIG _OT[]?0

VSS

–

PROTECTOR

REFERENCE

5VLDO

(User)

ToCOV-CUVCircuits

VBAT

bq76PL536

www.ti.com

SLUSA08A – DECEMBER 2009 – REVISED JULY 2010

Overtemperature Detection

When the temperature input TS1 or TS2 exceeds the programmed OT1 or OT2 threshold (CONFIG_OT[]) for a

period of time greater than OTT (CONFIG_OTT[]) the ALERT_STATUS[OT1, OT2] flag is set. The ALERT[] flags

are then ORed into the DEVICE_STATUS[ALERT] flag, and the ALERT_S (_H) pin is also asserted. The OT flag

is latched unless OTT is programmed to 0, in which case the flag follows the fault condition. Care should be

taken when using this setting to avoid chatter of the fault status. To reset the FAULT flag, first remove the source

of the alert (i.e., the overtemperature condition) and then write a 1 to ALERT[OTn], followed by a 0 to

FAULT[OTn].

Figure 7. Simplified Overtemperature Detection Schematic

As shown in the drawing above, the OT thresholds are detectable in 11 steps representing approximately 5°C

divisions when a thermistor and gain/offset setting resistors are chosen using the formula in the External

Temperature Sensor Support (TS1+, TS1– and TS2+, TS2–) section. A DISABLED setting is also available. This

results in an adjustment range from approximately 40°C to 90°C, but the range center can be moved by

modifying the RT value. The steps are spaced in a non-linear fashion to correspond to typical thermistor

response curves. Typical accuracy of a few degrees C or better can be achieved (with no additional calibration

requirements) by careful selection of the thermistor and resistors.

Each input sensor can be adjusted independently via separate registers CONFIG_OT1[] and CONFIG_OT2[].

The two temperature setpoints share a common filter delay set in the CONFIG_OTT[] register. A setting of 0 in

the CONFIG_OTT[] register causes the fault sensing to be both instantaneous and not latched. All other settings

provide a latched ALERT state.

Ratiometric Sensing

The OT protector circuits use ratiometric inputs to sense fault conditions. The REG50 output is applied internally

to the divider which forms the reference voltages used by the comparator circuit. It is also used externally as the

excitation source for the temperature sensor. This allows the REG50 output to vary over time or temperature

(within data-sheet limits) and have virtually no effect on the correct operation of the circuit. Any change seen by

the sensor is also seen by the divider, and therefore, changes proportionally. Although it is valid to represent the

trip setpoints as voltages if you assume that REG50 is at exactly 5 V, in practice, this is not the case. In the chart

included in the next section, the correct ratios [RB/(RB + RT + RTH)] are shown, along with the equivalent voltage

points when REG50 is assumed to be 5 V.

Table 2. Overtemperature Trip Setpoints

OT THRESHOLDS

CONFIG_OT

TNOM °C

VTS RATIO SET

VTS RATIO CLEAR

VSET

(1)

VCLEAR

(1)

Disabled

(1)

Assumes REG50 = 5.000 V

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