7 Detailed Description

7.1 Overview

The REF80 is temperature controlled, buried zener voltage references specifically designed for excellent voltage

stability over time and temperature. The Figure 7-1 is the simplified block diagram of the REF80 showing the

generation of voltage reference with buried zener and on chip heater control.

7.2 Functional Block Diagram

OP-STBL

VDD

T-SET

REF_Z

REF_GND

HEATP

HEATM

Error amp

Heater

Regulator

Buried Zener

Reference

Figure 7-1. Functional Block Diagram for REF80

7.3 Feature Description

7.3.1 Heater

REF80 has on chip heater which is factory programmed to TSET temperature as per TSET of Heater to regulate

the temperature of the die within ± 1ºC, for the entire operating ambient temperature range. This allows

REF80 to achieve ultra low temperature drift of 0.05ppm/ ºC. Heater has dedicated supply pins HEATP and

HEATM which run independent of VDD supply pin. The steady state power dissipation of the heater is directly

proportional to the difference between ambient temperature TA and TSET as per Equation 1. Heater current

depends on (HEATP - HEATM) voltage. Heater takes high transient current at the time of start-up to heat up

the device from ambient. REF80 has heater indicator pin OP_STBL, which de-asserts when the heater reaches

within ±0.1% of TSET.

TSET of Heater

Operating Temperature Range

TSET

0ºC to 70ºC

115ºC

PHEATER=TSET − TA

RθJA  − VDD×IVDD

(1)

VDD is supply voltage for the chip and IVDD is the supply current.

RθJA depends on board thickness and layout. The data sheet value of RθJA is based on JEDEC standard board.

REF80 offers flexibility to decrease the heater temperature by putting a resistor on the T-SET pin as per T-SET

Pin Resistor VS Change in TSET to save power and reduce the thermal noise for restricted ambient temperature

applications. TSET must be programmed to 45ºC above the max ambient temperature to make sure that the

heater is regulating the temperature properly. REF80 samples the value of the resistor at the time of startup and

the value of TSET is modified accordingly. Small drift in resistor value will not impact the TSET temperature as

T-SET pin samples discreet value.

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REF80

SNAS856 – SEPTEMBER 2024

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