LT1766EFE#TRPBF Linear Technology, LT1766EFE#TRPBF Datasheet - Page 15

• Manufacturer Part Number: LT1766EFE#TRPBF
• Description: IC REG SW HV 1.5A 200KHZ 16TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1766EFE#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.2 ~ 54 V
• Current - Output: 1.5A
• Frequency - Switching: 200kHz
• Voltage - Input: 5.5 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
frequency decreases roughly linearly down to a limit
of about 40kHz. This lower oscillator frequency during
short-circuit conditions can then maintain control with
the effective minimum on time.
It is recommended that for [V
a soft-start circuit should be used to control the output
capacitor charge rate during start-up or during recovery
from an output short circuit, thereby adding additional
control over peak inductor current. See Buck Converter
with Adjustable Soft-Start later in this data sheet.
OUTPUT CAPACITOR
The output capacitor is normally chosen by its effective
series resistance (ESR), because this is what determines
output ripple voltage. To get low ESR takes volume , so
physically smaller capacitors have high ESR. The ESR
range for typical LT1766 applications is 0.05Ω to 0.2Ω.
A typical output capacitor is an AVX type TPS, 100μF at
10V, with a guaranteed ESR less than 0.1Ω. This is a “D”
size surface mount solid tantalum capacitor. TPS capaci-
tors are specially constructed and tested for low ESR, so
they give the lowest ESR for a given volume. The value
in microfarads is not particularly critical, and values from
22μF to greater than 500μF work well, but you cannot
cheat mother nature on ESR. If you fi nd a tiny 22μF solid
tantalum capacitor, it will have high ESR, and output ripple
voltage will be terrible. Table 2 shows some typical solid
tantalum surface mount capacitors.
Table 3. Surface Mount Solid Tantalum Capacitor ESR
and Ripple Current
E Case Size
AVX TPS, Sprague 593D
D Case Size
AVX TPS, Sprague 593D
C Case Size
AVX TPS
Many engineers have heard that solid tantalum capacitors
are prone to failure if they undergo high surge currents. This
is historically true, and type TPS capacitors are specially
tested for surge capability, but surge ruggedness is not
a critical issue with the output capacitor. Solid tantalum
ESR (MAX, Ω )
0.1 to 0.3
0.1 to 0.3
0.2 (typ)
IN
/(V
OUT
+ V
RIPPLE CURRENT (A)
F
)] ratios > 10,
0.7 to 1.1
0.7 to 1.1
0.5 (typ)
capacitors fail during very high turn-on surges, which
do not occur at the output of regulators. High discharge
surges, such as when the regulator output is dead shorted,
do not harm the capacitors.
Unlike the input capacitor, RMS ripple current in the output
capacitor is normally low enough that ripple current rating
is not an issue. The current waveform is triangular with
a typical value of 125mA
this is:
Output capacitor ripple current (RMS):
Ceramic Capacitors
Higher value, lower cost ceramic capacitors are now
becoming available. They are generally chosen for their
good high frequency operation, small size and very low
ESR (effective series resistance). Their low ESR reduces
output ripple voltage but also removes a useful zero in the
loop frequency response, common to tantalum capaci-
tors. To compensate for this, a resistor R
in series with the V
must be taken however, since this resistor sets the high
frequency gain of the error amplifi er, including the gain at
the switching frequency. If the gain of the error amplifi er
is high enough at the switching frequency, output ripple
voltage (although smaller for a ceramic output capacitor)
may still affect the proper operation of the regulator. A
fi lter capacitor, C
suggested to control possible ripple at the V
Ceramic solution is possible for the LT1766 by choos-
ing the correct compensation components for the given
application.
Example: For V
LT1766 can be stabilized, provide good transient response
and maintain very low output ripple voltage using the
following component values: (refer to the fi rst page of
this data sheet for component references) C3 = 2.2μF ,
R
Application Note 19 for further detail on techniques for
proper loop compensation.
C
I
RIPPLE RMS
= 4.7k, C
(
C
)
= 15nF , C
IN
=
F
, in parallel with the R
0 29
= 8V to 40V, V
.
C
compensation capacitor, C
(
LT1766/LT1766-5
V
F
( )( )( )
OUT
RMS
L f V
= 220pF and C1 = 47μF . See
)
. The formula to calculate
(
V
IN
IN
OUT
−
V
OUT
= 3.3V at 1A, the
C
C
/C
)
can be placed
C
C
network is
pin. An All
15
C
. Care
1766fc