參數(shù)資料
型號(hào): LBKF
廠商: Linear Technology Corporation
英文描述: 100mA, Low Voltage, Very Low Dropout Linear Regulator
中文描述: 100mA的,低電壓,非常低壓差線性穩(wěn)壓器
文件頁數(shù): 10/16頁
文件大?。?/td> 219K
代理商: LBKF
10
LT3020/LT3020-1.2/
LT3020-1.5/LT3020-1.8
sn3020 3020fas
APPLICATIOU
W
U
U
No-Load/Light-Load Recovery
A possible transient load step that occurs is where the
output current changes from its maximum level to zero
current or a very small load current. The output voltage
responds by overshooting until the regulator lowers the
amount of current it delivers to the new level. The regulator
loop response time and the amount of output capacitance
control the amount of overshoot. Once the regulator has
decreased its output current, the current provided by the
resistor divider (which sets V
OUT
) is the only current
remaining to discharge the output capacitor from the level
to which it overshot. The amount of time it takes for the
output voltage to recover easily extends to milliseconds
with microamperes of divider current and a few microfar-
ads of output capacitance.
To eliminate this problem, the LT3020 incorporates a
no-load or light-load recovery circuit. This circuit is a
voltage-controlled current sink that significantly improves
the light load transient response time by discharging the
output capacitor quickly and then turning off. The current
sink turns on when the output voltage exceeds 6% of the
nominal output voltage. The current sink level is then
proportional to the overdrive above the threshold up to a
maximum of approximately 15mA. Consult the curve in
the Typical Performance Characteristics for the No-Load
Recovery Threshold.
If external circuitry forces the output above the no load
recovery circuit’s threshold, the current sink turns on in an
attempt to restore the output voltage to nominal. The
current sink remains on until the external circuitry releases
the output. However, if the external circuitry pulls the
output voltage above the input voltage, or the input falls
below the output, the LT3020 turns the current sink off and
shuts down the bias current/reference generator circuitry.
Thermal Considerations
The LT3020’s power handling capability is limited by its
maximum rated junction temperature of 125
°
C. The power
dissipated by the device is comprised of two components:
1. Output current multiplied by the input-to-output volt-
age differential: (I
OUT
)(V
IN
– V
OUT
) and
2. GND pin current multiplied by the input voltage:
(I
GND
)(V
IN
).
GND pin current is found by examining the GND pin
current curves in the Typical Performance Characteristics.
Power dissipation is equal to the sum of the two compo-
nents listed above.
DC BIAS VOLTAGE (V)
C
3020 F02
20
0
–20
–40
–60
–80
–1000
4
8
10
2
6
12
14
X5R
Y5V
16
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10
μ
F
TEMPERATURE (
°
C)
–50
40
20
0
–20
–40
–60
–80
–100
25
75
3020 F03
–25
0
50
100
125
Y5V
C
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10
μ
F
Figure 2. Ceramic Capacitor DC Bias Characteristics
Figure 3. Ceramic Capacitor Temperature Characteristics
1ms/DIV
3020 F04
1mV/DIV
V
OUT
= 1.3V
C
OUT
= 10
μ
F
I
LOAD
= 0
Figure 4. Noise Resulting from Tapping on a Ceramic Capacitor
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