9 Detailed Description

9.1 Overview

The REF35-Q1 is family of ultralow 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-Q1 showing basic band-gap topology.

9.2 Functional Block Diagram

VIN

Digital

Core

Bandgap

Core

R

Buffer

EN

Control

EN

GND

NR

VREF

Rp

VIN

Rp for

Open Drain

EN control

9.3 Feature Description

9.3.1 Supply Voltage

The REF35-Q1 family of references features an extremely low dropout voltage. For 10 mA loaded conditions,

a maximum dropout voltage is 250 mV. Figure 7-25 shows a typical dropout voltage (VDO) versus load current.

The device supports operation with input voltage range from VREF + VDO to 6 V. The typical quiescent current is

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

ultral-ow current enable the operation across multiple battery powered applications.

9.3.2 EN Pin

The REF35-Q1 family supports device enable and disable functionality through logic level control on EN pin. The

EN pin of REF35-Q1 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, the device is

in active mode. When EN pin is drive by an open-drain outputs, 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 50 nA.

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 Section 7.5 for logic high and logic low voltage levels.

9.3.3 NR Pin

The REF35-Q1 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-Q1

SNAS845 – AUGUST 2023

Copyright © 2023 Texas Instruments Incorporated

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Product Folder Links: REF35-Q1