参数资料
型号: LTC3809EMS-1
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 1 A SWITCHING CONTROLLER, 600 kHz SWITCHING FREQ-MAX, PDSO10
封装: PLASTIC, MSOP-10
文件页数: 8/24页
文件大小: 318K
代理商: LTC3809EMS-1
LTC3809-1
38091f
16
APPLICATIO S I FOR ATIO
WU
UU
For most applications, a 59k resistor is suggested for RA.
In applications where minimizing the quiescent current is
critical, RA should be made bigger to limit the feedback
divider current. If RB then results in very high impedance,
it may be beneficial to bypass RB with a 50pF to 100pF
capacitor CFF.
Figure 3. Setting Output Voltage
Figure 4. RUN Pin Interfacing
LTC3809-1
VFB
VOUT
RB
CFF
RA
38091 F03
3.3V OR 5V
38091 F04
LTC3809-1
RUN
LTC3809-1
RUN
LTC3809-1
VFB
VOUT
VX
TRACK/SS
RB
RA
38091 F5a
RTB
RTA
Run and Soft-Start/Tracking Functions
The LTC3809-1 has a low power shutdown mode which is
controlled by the RUN pin. Pulling the RUN pin below 1.1V
puts the LTC3809-1 into a low quiescent current shut-
down mode (IQ = 9A). Releasing the RUN pin, an internal
0.7
A (at VIN = 4.2V) current source will pull the RUN pin
up to VIN, which enables the controller. The RUN pin can
be driven directly from logic as showed in Figure 4.
Once the controller is enabled, the start-up of VOUT is
controlled by the state of the TRACK/SS pin. If the TRACK/
SS pin is connected to VIN, the start-up of VOUT is con-
trolled by internal soft-start, which slowly ramps the
positive reference to the error amplifier from 0V to 0.6V,
allowing VOUT to rise smoothly from 0V to its final value.
The default internal soft-start time is around 0.74ms. The
soft-start time can be changed by placing a capacitor
between the TRACK/SS pin and GND. In this case, the soft-
start time will be approximately:
tC
mV
A
SS
=
600
1
where 1
A is an internal current source which is
always on.
When the voltage on the TRACK/SS pin is less than the
internal 0.6V reference, the LTC3809-1 regulates the VFB
voltage to the TRACK/SS pin voltage instead of 0.6V.
Therefore the start-up of VOUT can ratiometrically track an
external voltage VX, according to a ratio set by a resistor
divider at TRACK/SS pin (Figure 5a). The ratiometric
relation between VOUT and VX is (Figure 5c):
V
R
RR
OUT
X
TA
A
AB
TA
TB
=
+
Figure 5a. Using the TRACK/SS Pin to Track VX
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