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參數(shù)資料
| 型號(hào)： | LTC3642IMS8E-3.3E#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.13 A SWITCHING REGULATOR, PDSO8 |
| 封裝： | LEAD FREE, PLASTIC, MSOP-8 |
| 文件頁數(shù)： | 5/20頁 |
| 文件大小： | 306K |
| 代理商： | LTC3642IMS8E-3.3E#PBF |
LTC3642
13
3642fa
APPLICATIONS INFORMATION
The resistive divider allows the VFB pin to sense a fraction
of the output voltage as shown in Figure 6.
VFB
LTC3642
GND
VOUT
R2
R1
Figure 6. Setting the Output Voltage
To minimize the no-load supply current, resistor values in
the megohm range should be used. The increase in supply
current due to the feedback resistors can be calculated
from:
ΔI
V
RR
V
VIN
OUT
IN
=
+
12
Run Pin with Programmable Hysteresis
The LTC3642 has a low power shutdown mode controlled
by the RUN pin. Pulling the RUN pin below 0.7V puts the
LTC3642 into a low quiescent current shutdown mode
(IQ ~ 3μA). When the RUN pin is greater than 1.2V,
the controller is enabled. Figure 7 shows examples of
congurations for driving the RUN pin from logic.
LTC3642
RUN
4.7M
VIN
3642 F07
LTC3642
RUN
VSUPPLY
Figure 7. RUN Pin Interface to Logic
The RUN pin can alternatively be congured as a precise
undervoltage lockout (UVLO) on the VIN supply with
a resistive divider from VIN to ground. The RUN pin
comparator nominally provides 10% hysteresis when
used in this method; however, additional hysteresis may
be added with the use of the HYST pin. The HYST pin is
an open-drain output that is pulled to ground whenever
the RUN comparator is not tripped. A simple resistive
divider can be used as shown in Figure 8 to meet specic
VIN voltage requirements.
Specic values for these UVLO thresholds can be computed
from the following equations:
Ri
g V UVLO Threshold
V
R
IN
sin
.
=+
121
1
2
=+
+
Fall g V UVLO Threshold
V
R
RR
IN
in
.
110
1
2
3
The minimum value of these thresholds is limited to
the internal VIN UVLO thresholds that are shown in the
Electrical Characteristics table. The current that ows
through this divider will directly add to the shutdown,
sleep and active current of the LTC3642, and care should
be taken to minimize the impact of this current on the
overall efciency of the application circuit. Resistor values
in the megohm range may be required to keep the impact
on quiescent shutdown and sleep currents low. Be aware
that the HYST pin cannot be allowed to exceed its absolute
maximum rating of 6V. To keep the voltage on the HYST
pin from exceeding 6V, the following relation should be
satised:
V
R
RR
R
V
IN MAX
()
3
12
3
6
++
<
The RUN pin may also be directly tied to the VIN supply
for applications that do not require the programmable
undervoltage lockout feature. In this conguration, switch-
ing is enabled when VINsurpassestheinternalundervoltage
lockout threshold.
Soft-Start
The internal 0.75ms soft-start is implemented by ramping
both the effective reference voltage from 0V to 0.8V and the
peak current limit set by the ISET pin (25mA to 115mA).
RUN
LTC3642
HYST
VIN
R2
R1
R3
3642 F08
Figure 8. Adjustable Undervoltage Lockout
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