LTC1436AIGN-PLL#TR Linear Technology, LTC1436AIGN-PLL#TR Datasheet - Page 12

• Manufacturer Part Number: LTC1436AIGN-PLL#TR
• Description: IC REG SW SYNC STEPDWN LN 24SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1436AIGN-PLL#TR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.19 ~ 9 V
• Current - Output: 50mA
• Frequency - Switching: 125kHz ~ 240kHz
• Voltage - Input: 3.5 ~ 30 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: LTC1436AIGN-PLLTR

LTC1436A
LTC1436-PLL-A/LTC1437A
APPLICATIONS
A graph for selecting C
2. As the operating frequency is increased the gate
charge losses will be higher, reducing efficiency (see
Efficiency Considerations). The maximum recommended
switching frequency is 400kHz. When using Figure 2 for
synchronizable applications, choose C
ing to a frequency approximately 30% below your center
frequency. (See Phase-Locked Loop and Frequency Syn-
chronization.)
Inductor Value Calculation
The operating frequency and inductor selection are inter-
related in that higher operating frequencies allow the use
of smaller inductor and capacitor values. So why would
anyone ever choose to operate at lower frequencies with
larger components? The answer is efficiency. A higher
frequency generally results in lower efficiency because of
MOSFET gate charge losses. In addition to this basic
trade-off, the effect of inductor value on ripple current and
low current operation must also be considered.
The inductor value has a direct effect on ripple current. The
inductor ripple current ∆I
tance or frequency and increases with higher V
12
C
OSC
( )
pF
300
250
200
150
100
50
0
0
=
Figure 2. Timing Capacitor Value
⎡
⎢
⎢
⎣
Frequency kHz
100
OPERATING FREQUENCY (kHz)
U
1 37 10
. (
OSC
200
INFORMATION
L
U
vs frequency is given in Figure
decreases with higher induc-
4
( )
300
)
V
PLLLPF
⎤
⎥
⎥
⎦
W
400
–
11
= 0V
OSC
1436 F02
500
correspond-
IN
U
or V
OUT
:
Accepting larger values of ∆I
inductances, but results in higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is ∆I
maximum ∆I
The inductor value also has an effect on low current
operation. The transition to low current operation begins
when the inductor current reaches zero while the bottom
MOSFET is on. Lower inductor values (higher ∆I
cause this to occur at higher load currents, which can
cause a dip in efficiency in the upper range of low current
operation. In Burst Mode operation (TGS pin open),
lower inductance values will cause the burst frequency to
decrease.
The Figure 3 graph gives a range of recommended induc-
tor values vs operating frequency and V
For low duty cycle, high frequency applications where the
required minimum on-time,
is less than 350ns, there may be further restrictions on the
inductance to ensure proper operation. See Minimum On-
Time Considerations section for more details.
∆I
t
ON MIN
L
(
=
( )( )
Figure 3. Recommended Inductor Values
f L
)
1
60
50
40
30
20
10
=
0
L
0
(
occurs at the maximum input voltage.
V
V
OUT
IN MAX
50
V
(
OPERATING FREQUENCY (kHz)
OUT
⎛
⎜
⎝
1
100
−
)
)( )
V
f
L
V
OUT
IN
= 0.4 (I
150
⎞
⎟
⎠
L
200
allows the use of low
V
V
V
MAX
OUT
OUT
OUT
250
= 5V
= 3.3V
≤ 2.5V
). Remember, the
OUT
1436 F03
300
.
L
14367afb
) will