AAT3190 データシートの表示（PDF） - Advanced Analogic Technologies

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AAT3190

Positive/Negative Charge Pump for Voltage Bias

Advanced Analogic Technologies 

AAT3190

Positive/Negative Charge Pump for Voltage Bias

Voltage Reference

The voltage reference is a simple band gap with an

output voltage equal to VBE + K*VT. The band gap

reference amplifier has an additional compensation

capacitor from the negative input to the output. This

capacitor serves to slow down the circuit during

startup and soft starts the voltage reference and

the regulator output from overshoot. The reference

circuit amplifier also increases the overall PSRR of

the device. An 80kΩ resistor serves to isolate and

buffer the amplifier from a small internal filter

capacitor and an optional large external filter

capacitor.

Enable and Start-up

The AAT3190 is disabled by pulling the EN pin low.

The threshold levels lie between 0.5V and 1.5V.

Even though the quiescent current of the IC during

shutdown is less than 1µA, the positive output volt-

age (VOP) and any load current associated with it

does not disappear without the complete removal of

the input voltage. This is due to the fact that with no

switching of the DRVP pin, the input voltage simply

forward biases the Schottky diodes associated with

the VOP charge pump, providing a path for load cur-

rent to be drawn from the input voltage.

Depending on the application, the supplies must be

sequenced properly to avoid damage or latch-up.

The AAT3190 start-up sequence ramps up the VOP

output 200µs after the VON output is present. The

AAT3190-1 ramps up the positive supply before the

negative supply.

Over-Temperature Protection

A logic control circuit will shut down both charge

pumps in the case of an over-temperature condition.

Under-Voltage Lockout

A UVLO circuit disables the AAT3190 when the

input voltage supply is lower than 1.8V nominal.

Design Procedure and

Component Selection

Output Voltage

The number of charge pump stages required for a

given output varies with the input voltage applied.

The number of stages required can be estimated by:

np =

VOP - VIN

VIN - 2VF

for the positive output and

nn =

VON

2VF - VIN

for the negative output.

When solving for np and nn, round up the solution

to the next highest integer to determine the number

of stages required.

VON

The negative output voltage is adjusted by a resis-

tive divider from the output (VON) to the FBN and

REF pin.

The maximum reference voltage current is 50µA;

therefore, the minimum allowable value for R2 of

Figure 1 is 24kΩ. It is best to select the smallest

value possible for R2, as this will keep R1 to a min-

imum. This limits errors due to the FBN input bias

current. The FBN input has a maximum input bias

current of 100nA. Using the full 50µA reference

current for programming VON:

IPGM =

VREF

R2

=

1.2

24.1k =

50µA

will limit the error due to the input bias current at

FBN to less than 0.2%:

IFBN

IPGM

=

0.1µA

50µA

=

0.2%

10

3190.2006.01.1.2

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