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參數(shù)資料
| 型號(hào)： | AAT3190ITP-1-T1 |
| 廠商： | Advanced Analogic Technologies, Inc. |
| 英文描述： | Positive/Negative Charge Pump for Voltage Bias |
| 中文描述： | 正/負(fù)電荷泵電壓偏置 |
| 文件頁數(shù)： | 10/16頁 |
| 文件大?。?/td> | 411K |
| 代理商： | AAT3190ITP-1-T1 |
AAT3190
Positive/Negative Charge Pump for Voltage Bias
10
3190.2005.03.1.0
Voltage Reference
The voltage reference is a simple band gap with an
output voltage equal to b V
BE
+ K*V
T
. The band
gap reference amplifier has an additional compen-
sation capacitor from the negative input to the out-
put. This capacitor serves to slow down the circuit
during startup and soft starts the voltage reference
and the regulator output from overshoot. The refer-
ence circuit amplifier also increases the overall
PSRR of the device. An 80k
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 (V
OP
) 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 V
OP
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 V
OP
output 200μsec after the V
ON
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:
for the positive output and
for the negative output.
When solving for n
p
and n
n
, round up the solution
to the next highest integer to determine the number
of stages required.
V
ON
The negative output voltage is adjusted by a resis-
tive divider from the output (V
ON
) to the FBN and
REF pin.
The maximum reference voltage current is 50μA;
therefore, the minimum allowable value for R2 of
Figure 1 is 24k
. 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 V
ON
:
will limit the error due to the input bias current at
FBN to less than 0.2%:
I
FBN
I
PGM
=
= 0.2%
0.1
μ
A
50
μ
A
V
REF
R2
I
PGM
=
=
= 50
μ
A
1.2
24.1k
V
ON
2V
F
- V
IN
n
n
=
V
OP
- V
IN
V
IN
- 2V
F
n
p
=
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