LT3689EUD-5#PBF Linear Technology, LT3689EUD-5#PBF Datasheet - Page 13

• Manufacturer Part Number: LT3689EUD-5#PBF
• Description: IC BUCK 5V 0.7A 16QFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT3689EUD-5#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 700mA
• Frequency - Switching: 350kHz ~ 2.2MHz
• Voltage - Input: 3.6 ~ 36 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-WQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose 1% resistors
according to:
For reference designators, refer to the Block Diagram.
Setting the Switching Frequency
The LT3689 uses a constant-frequency PWM architecture
that can be programmed to switch from 350kHz to 2.2MHz
by using a resistor tied from the RT pin to ground. Table
1 shows the R
Table 1. Switching Frequency vs R
SWITCHING FREQUENCY (MHz)
R1= R2
0.8V
0.35
V
0.5
0.6
0.7
0.8
0.9
1.2
1.4
1.6
1.8
2.2
OUT
1
2
T
values for various switching frequencies.
1
T
R
T
31.6
24.9
20.5
16.9
14.7
12.7
9.53
6.04
4.87
4.02
3.16
48.7
7.5
(kΩ)
Operating Frequency Trade-Offs
Selection of the operating frequency is a trade-off be-
tween efficiency, component size and maximum input
voltage. The advantage of high frequency operation is
that smaller inductor and capacitor values may be used.
The disadvantages are lower efficiency, and narrower
input voltage range at constant-frequency. The highest
constant-switching frequency (f
plication can be calculated as follows:
where V
voltage, V
the internal switch drop (~0.5V at maximum load). If the
LT3689 is programmed to operate at a frequency higher
than f
enters pulse-skipping mode, where it skips switching
cycles to maintain regulation. At frequencies higher than
f
frequency. The LT3689 enters pulse-skipping mode at
frequencies higher than f
tion on the LT3689’s minimum on-time of 130ns. As the
switching frequency is increased above f
is required to switch for shorter periods of time to maintain
the same duty cycle. Delays associated with turning off
the power switch dictate the minimum on-time of the part.
When the required on-time decreases below the minimum
on-time of 130ns, the switch pulse width remains fixed at
130ns (instead of becoming narrower to accommodate
the duty cycle requirement). The inductor current ramps
up to a value exceeding the load current and the output
ripple increases. The part then remains off until the output
voltage dips below the programmed value before it begins
switching again.
SW(MAX)
f
SW(MAX)
SW(MAX)
IN
, the LT3689 no longer operates with constant-
D
is the typical input voltage, V
is the catch diode drop (~0.5V) and V
=
for a given V
t
ON(MIN)
V
LT3689/LT3689-5
(
OUT
V
SW(MAX)
IN
IN
– V
+ V
input voltage, the LT3689
SW(MAX)
SW
D
because of the limita-
+ V
D
OUT
SW(MAX)
) for a given ap-
)
is the output
, the part
13
SW
3689fd
is