LT3970EMS-5#PBF Linear Technology, LT3970EMS-5#PBF Datasheet - Page 9

• Manufacturer Part Number: LT3970EMS-5#PBF
• Description: IC BUCK 5V 0.35A 10MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT3970EMS-5#PBF

• 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-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

OPERATION
The LT3970 is a constant frequency, current mode step-
down regulator. An oscillator, with frequency set by RT,
sets an RS fl ip-fl op, turning on the internal power switch.
An amplifi er and comparator monitor the current fl owing
between the V
this current reaches a level determined by the voltage at
V
output voltage through an external resistor divider tied to
the FB pin and servos the V
output increases, more current is delivered to the output;
if it decreases, less current is delivered.
Another comparator monitors the current fl owing through
the catch diode and reduces the operating frequency when
the current exceeds the 400mA bottom current limit. This
foldback in frequency helps to control the output current
in fault conditions such as a shorted output with high
input voltage. Maximum deliverable current to the output
is therefore limited by both switch current limit and catch
diode current limit.
An internal regulator provides power to the control cir-
cuitry. The bias regulator normally draws power from
the V
voltage higher than 3.2V, bias power will be drawn from
the external source (typically the regulated output voltage).
This improves effi ciency.
C
(see Block Diagram). An error amplifi er measures the
IN
pin, but if the BD pin is connected to an external
IN
and SW pins, turning the switch off when
C
node. If the error amplifi er’s
If the EN pin is low, the LT3970 is shut down and draws
0.7μA from the input. When the EN pin exceeds 1V, the
switching regulator will become active.
The switch driver operates from either V
BOOST pin. An external capacitor is used to generate a
voltage at the BOOST pin that is higher than the input
supply. This allows the driver to fully saturate the internal
bipolar NPN power switch for effi cient operation.
To further optimize effi ciency, the LT3970 automatically
switches to Burst Mode operation in light load situations.
Between bursts, all circuitry associated with controlling
the output switch is shut down reducing the input supply
current to 1.7μA.
The LT3970 contains a power good comparator which
trips when the FB pin is at 90% of its regulated value. The
PG output is an open-drain transistor that is off when the
output is in regulation, allowing an external resistor to pull
the PG pin high. Power good is valid when the LT3970 is
enabled and V
LT3970/LT3970-3.3/LT3970-5
IN
is above 4.2V.
IN
or from the
3970fa
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