Precision, Micropower,

Low-Dropout Voltage References

12

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Detailed Description

The MAX6190–MAX6195/MAX6198 precision bandgap

references use a proprietary curvature-correction circuit

and laser-trimmed thin-film resistors, resulting in a low

temperature coefficient of <5ppm/°C and initial accura-

cy of better than 0.1%. These devices can sink and

source up to 500µA with <200mV of dropout voltage,

making them attractive for use in low-voltage applica-

tions.

Applications Information

Output/Load Capacitance

Devices in this family do not require an output capaci-

tance for frequency stability. They are stable for capac-

itive loads from 0 to 2.2nF. However, in applications

where the load or the supply can experience step

changes, an output capacitor will reduce the amount of

overshoot (or undershoot) and assist the circuit’s tran-

sient response. Many applications do not need an

external capacitor, and this family can offer a signifi-

cant advantage in these applications when board

space is critical.

Supply Current

The quiescent supply current of these series-mode ref-

erences is a maximum of 35µA and is virtually indepen-

dent of the supply voltage, with only a 0.8µA/V variation

with supply voltage. Unlike series references, shunt-

mode references operate with a series resistor connect-

ed to the power supply. The quiescent current of a

shunt-mode reference is thus a function of the input

voltage. Additionally, shunt-mode references have to

be biased at the maximum expected load current, even

if the load current is not present all the time. In the

series-mode MAX6190 family, the load current is drawn

from the input voltage only when required, so supply

current is not wasted and efficiency is maximized at all

input voltages. This improved efficiency can help

reduce power dissipation and extend battery life.

When the supply voltage is below the minimum speci-

fied input voltage (as during turn-on), the devices can

draw up to 200µA beyond the nominal supply current.

The input voltage source must be capable of providing

this current to ensure reliable turn-on.

Output Voltage Hysteresis

Output voltage hysteresis is the change in the output

cycled over its entire operating temperature range.

Hysteresis is caused by differential package stress

appearing across the bandgap core transistors. The

typical temperature hysteresis value is 75ppm.

Turn-On Time

These devices typically turn on and settle to within

0.1% of their final value in 30µs to 220µs, depending on

the device. The turn-on time can increase up to 1.5ms

with the device operating at the minimum dropout volt-

age and the maximum load.

Positive and Negative Low-Power

Voltage Reference

Figure 1 shows a typical method for developing a bipo-

lar reference. The circuit uses a MAX681 voltage dou-

bler/inverter charge-pump converter to power an

ICL7652, thus creating a positive as well as a negative

reference voltage.

NAME

FUNCTION

1, 3, 5, 7,

8

N.C.

No Connection. Not internally

connected.

PIN

4

GND

Ground

Pin Description

6

OUT

Reference Voltage Output

2

IN

Supply Voltage Input