9 Detailed Description

9.1 Overview

The REF35 is family of ultra-low current, low-noise, precision band-gap voltage references that are specifically

designed for excellent initial voltage accuracy and drift. The Functional Block Diagram is a simplified block

diagram of the REF35 showing basic band-gap topology.

9.2 Functional Block Diagram

VIN

Digital

Core

Band-Gap

Core

R

Buffer

EN

Control

EN

GND

NR

VREF

VIN

Rp for

Open Drain

EN control

9.3 Feature Description

9.3.1 Supply Voltage

The REF35 family of references features an extremely low dropout voltage. For 10 mA loaded conditions, a

650 nA and maximum quiescent current over temperature is only 2.6 μA. The low dropout voltage coupled with

ultra-low current enable the operation across multiple battery powered applications.

9.3.2 EN Pin

The REF35 family supports device enable and disable functionality through logic level control on EN pin. The

EN pin of REF35 does not use an internal pull-up resistor. Instead, the pin uses new 'clean EN' technology. This

allows the EN pin to be in a no connect condition at start-up, and no extra current is drawn from the supply

when the EN pin is pulled low in shutdown mode. When EN pin is pulled high or left unconnected at start-up, the

device is in active mode. When EN pin is driven by an open-drain output, a pull-up resistor to VIN is required.

The device must be in active mode for normal operation. The EN pin must not be pulled higher than VIN supply

voltage.

The device can be placed in shutdown mode by pulling the EN pin low. When in shutdown mode, the output

of the device becomes high impedance and the quiescent current of the device drops to 100 nA at room

temperature. When changing the device state from shutdown to active state, ensure the EN pin is not left

floating.

Also note that for applications where EN pin is no-connect, total parasitic capacitance on EN pin should be

restricted within 30 pF.

See the Electrical Characteristics table for logic high and logic low voltage levels.

9.3.3 NR Pin

The REF35 pin allows access to the band-gap through the NR pin. Placing a capacitor from the NR pin to

GND creates a low-pass filter in combination with the internal resistance of 60 kΩ. Leakage of the capacitance

directly impacts the accuracy and temperature drift. If NR functionality is used, choose a low leakage capacitor.

A capacitance of 1 μF creates a low-pass filter with corner frequency around 2.7 Hz. Such a filter decreases

the overall noise on the VREF pin. Higher capacitance results in a lower filter cut off frequency, further reducing

output noise. Please note, using the capacitor on NR pin also increases start-up time.

www.ti.com

REF35

SNAS809A – DECEMBER 2021 – REVISED AUGUST 2022

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Product Folder Links: REF35