LT3970EDDB-5#TRPBF Linear Technology, LT3970EDDB-5#TRPBF Datasheet - Page 14

• Manufacturer Part Number: LT3970EDDB-5#TRPBF
• Description: IC BUCK 5V 0.35A 10DFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT3970EDDB-5#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 350mA
• Frequency - Switching: 200kHz ~ 2.25MHz
• Voltage - Input: 4.2 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
may not be fully charged. Because the boost capacitor is
charged with the energy stored in the inductor, the circuit
will rely on some minimum load current to get the boost
circuit running properly. This minimum load will depend
on input and output voltages, and on the arrangement of
the boost circuit. The minimum load generally goes to
zero once the circuit has started. Figure 5 shows a plot
of minimum load to start and to run as a function of input
voltage. In many cases the discharged output capacitor
will present a load to the switcher, which will allow it to
start. The plots show the worst-case situation where V
is ramping very slowly. For lower start-up voltage, the
boost diode can be tied to V
input range to one-half of the absolute maximum rating
of the BOOST pin.
Enable Pin
The LT3970 is in shutdown when the EN pin is low and
active when the pin is high. The rising threshold of the EN
comparator is 1V, with a 30mV hysteresis. This threshold is
accurate when V
tie EN pin to GND to place the part in shutdown.
14
Figure 4. Two Circuits for Generating the Boost Voltage
V
V
IN
IN
(4b) For V
IN
V
V
IN
IN
(4a) For V
is above 4.2V. If V
LT3970
LT3970
GND
GND
BD
BD
OUT
BOOST
BOOST
SW
SW
< 2.2V; V
OUT
IN
≥ 2.2V
; however, this restricts the
IN
C3
C3
< 27V
IN
is lower than 4.2V,
3970 F04
V
OUT
V
OUT
IN
Adding a resistor divider from V
LT3970 to regulate the output only when V
desired voltage (see Figure 6). This threshold voltage,
V
such that they satisfy the following equation:
where output regulation should not start until V
V
regulation will not stop until the input falls slightly below
V
IN(EN)
IN(EN)
IN(EN)
V
IN EN
(
Figure 5. The Minimum Input Voltage Depends on
Output Voltage, Load Current and Boost Circuit
, can be adjusted by setting the values R3 and R4
. Note that due to the comparator’s hysteresis,
.
)
=
4.0
5.5
5.0
4.5
3.5
3.0
2.5
6.5
6.0
5.0
4.5
4.0
R
0
0
3
FRONT PAGE APPLICATION
V
FRONT PAGE APPLICATION
V
TO RUN
TO START/RUN
R
OUT
OUT
+
4
50
50
R
= 3.3V
= 5V
4
100
100
•
TO START
LOAD CURRENT (mA)
LOAD CURRENT (mA)
1
V
150
150
200
200
250
250
IN
to EN programs the
300
300
3970 F05
350
350
IN
is above a
IN
is above
3970fa