9 Detailed Description

9.1 Overview

The REF35 is family of ultralow current, low-noise, precision bandgap 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

Bandgap

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

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 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, it uses a new 'clean EN' technology. This allows

EN pin to left floating and at the same time no extra current is drawn from the supply when EN pin is pulled low

in shut-down 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.

It is to be noted that for applications where EN pin is left floating, 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 pin allows access to the bandgap through the NR pin. Placing a capacitor from the NR pin to

GND creates a low-pass filter in combination with the internal resistance R. 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 TBD 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.

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REF35

SNAS809 – DECEMBER 2021

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Product Folder Links: REF35