LT1959CR#TRPBF Linear Technology, LT1959CR#TRPBF Datasheet - Page 11

• Manufacturer Part Number: LT1959CR#TRPBF
• Description: IC SW REG STEP-DWN 500KHZ 7-DD
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1959CR#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.21 ~ 38 V
• Current - Output: 4.5A
• Frequency - Switching: 500kHz
• Voltage - Input: 4.3 ~ 15 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (7 leads + tab)
• Dc To Dc Converter Type: Step Down
• Pin Count: 7 +Tab
• Input Voltage: 16V
• Output Voltage: 1.21 to 2.42V
• Switching Freq: 540kHz
• Output Current: 8.5A
• Package Type: DDPAK
• Output Type: Adjustable
• Switching Regulator: Yes
• Line Regulation: 0.03%/V
• Mounting: Surface Mount
• Input Voltage (min): 4V
• Operating Temperature Classification: Commercial
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Compliant

APPLICATIONS
Table 2
VENDOR/
PART NO.
Coiltronics
CTX2-1
CTX5-4
CTX8-4
CTX2-1P
CTX2-3P
CTX5-4P
Sumida
CDRH125
CDRH125
CDRH125
CDRH125
Coilcraft
DT3316-222
DT3316-332
DT3316-472
Pulse
PE-53650
PE-53651
PE-53652
PE-53653
Dale
IHSM-4825
IHSM-4825
IHSM-5832
IHSM-5832
IHSM-7832
Tor = Toroid
SC = Semiclosed geometry
Fer = Ferrite core material
52 = Type 52 powdered iron core material
KM = Kool M
Output Capacitor
The output capacitor is normally chosen by its Effective
Series Resistance (ESR), because this is what determines
output ripple voltage. At 500kHz, any polarized capacitor
is essentially resistive. To get low ESR takes volume , so
physically smaller capacitors have high ESR. The ESR
Kool M is a registered trademark of Magnetics, Inc.
VALUE
®
( H)
2.2
3.3
4.7
2.7
4.7
10
12
15
18
16
10
15
22
2
5
8
2
2
5
4
5
9
(Amps)
U
DC
4.1
4.4
3.5
3.4
4.6
3.3
4.0
3.5
3.3
3.0
4.8
5.4
5.5
5.1
5.1
4.0
4.3
3.5
3.8
5
5
3
INFORMATION
CORE
U
TYPE
Open
Open
Open
Open
Open
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
SC
SC
SC
SC
SC
SC
SC
TANCE( )
SERIES
RESIS-
0.011
0.019
0.020
0.014
0.012
0.027
0.025
0.027
0.030
0.034
0.035
0.040
0.045
0.017
0.018
0.022
0.032
0.034
0.047
0.053
0.078
0.054
W
MATER- HEIGHT
CORE
KM
KM
KM
IAL
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
52
52
52
52
52
52
52
U
(mm)
4.2
6.4
6.4
4.2
4.8
6.4
5.1
5.1
5.1
9.1
9.1
5.6
5.6
7.1
7.1
7.1
10
10
6
6
6
6
range for typical LT1959 applications is 0.05 to 0.2 . A
typical output capacitor is an AVX type TPS, 100 F at 10V,
with a guaranteed ESR less than 0.1 . This is a “D” size
surface mount solid tantalum capacitor. TPS capacitors
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
22 F to greater than 500 F work well, but you cannot
cheat mother nature on ESR. If you find a tiny 22 F solid
tantalum capacitor, it will have high ESR, and output ripple
voltage will be terrible. Table 3 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
AVX TAJ
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 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 cur-
rent rating is not an issue. The current waveform is
triangular with a typical value of 200mA
to calculate this is:
Output Capacitor Ripple Current (RMS):
I
RIPPLE RMS
0 29
V
OUT
ESR (Max.,
L f V
0.1 to 0.3
0.7 to 0.9
0.1 to 0.3
0.2 (typ)
V
IN
IN
V
)
OUT
RMS
Ripple Current (A)
. The formula
0.7 to 1.1
0.7 to 1.1
0.5 (typ)
LT1959
0.4
11