參數(shù)資料
型號(hào): LTC3620EDC-1#TRPBF
廠商: LINEAR TECHNOLOGY CORP
元件分類(lèi): 穩(wěn)壓器
英文描述: SWITCHING REGULATOR, 50 kHz SWITCHING FREQ-MAX, PDSO8
封裝: 2 X 2 MM, LEAD FREE, PLASTIC, DFN-8
文件頁(yè)數(shù): 4/18頁(yè)
文件大?。?/td> 318K
代理商: LTC3620EDC-1#TRPBF
LTC3620
12
3620fa
APPLICATIONS INFORMATION
Setting Output Voltage
The output voltage is set by tying VFB to a resistive divider
using the following formula (refer to Figure 3):
VOUT =
0.6V R1+ R2
()
R2
R1 and R2 should be large to minimize standing load
current and improve efciency.
The xed output version, the LTC3620-1, includes an
internal resistive divider, eliminating the need for external
resistors. The resistor divider is chosen such that the VFB
input current is approximately 1μA. For this version, the
VFB pin should be connected directly to VOUT.
Maximum Load Current and Maximum Frequency
The maximum current that the LTC3620 can provide is
calculated to be just slightly less than half the maximum
peak current.
The inductor value will determine how much energy is
delivered to the output for each switching cycle, and thus
the duration of each pulse and the maximum frequency.
Larger inductors will have slower ramp rates, longer pulses,
and thus lower maximum frequencies. Conversely, smaller
inductors will result in higher maximum frequencies.
When using a frequency clamp, large abrupt increasing
load steps from levels below the locking range to levels
near the maximum output may result in a large drop in
the output voltage. This is due to the low bandwidth of
the frequency clamp loop in returning the peak inductor
current to its maximum.
Thermal Considerations
The LTC3620 requires the package backplane metal to
be soldered to the PC board. This gives the DFN package
exceptional thermal properties, making it difcult in normal
operation to exceed the maximum junction temperature
of the part. In most applications the LTC3620 does not
dissipate much heat due to its high efciency and low
current. In applications where the LTC3620 is running at
high ambient temperatures and high load currents, the heat
dissipated may exceed the maximum junction temperature
of the part if it is not well thermally grounded.
Design Example
This example designs a 1.1V output using a Li-Ion battery
input with voltages between 2.8V to 4.2V, and an average
of 3.6V. The internally provided 50kHz clock will be used
for the minimum switching frequency, so the FMIN/MODE
pin will be pulled low. For a 1.1V output, an 18μH inductor
should be used (refer to Table 2).
COUT can be chosen from Table 2 or can be based on a
desired maximum output voltage ripple, ΔVOUT. For this
case let’s use a maximum ΔVOUT equal to 1% of VOUT,
or 11mV.
COUT =
35mA
2
() 22H
() 3.6V
()
2ΔVOUT 1.1V
() 3.6V – 1.1V
()
= 1.6F ≈ 1.5F
Figure 3. Design Example Schematic
VIN
RUN
1μF
CER
COUT
LOBATB
VIN
2.9V TO 5.5V
VOUT
1.1V
R2
3620 F03
R1
1M
L
22pF
LTC3620
SW
VFB
FMIN/MODE
GND
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