LM5005MH National Semiconductor, LM5005MH Datasheet - Page 19

• Manufacturer Part Number: LM5005MH
• Description: IC, BUCK REGULATOR, TSSOP-20
• Manufacturer: National Semiconductor

Specifications of LM5005MH

• Primary Input Voltage: 75V
• No. Of Outputs: 1
• Output Voltage: 1.225V
• Output Current: 2.5A
• No. Of Pins: 20
• Operating Temperature Range: -40°C To +125°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application Information
PWB BOARD LAYOUT AND THERMAL
CONSIDERATIONS
The circuit in Figure 1 serves as both a block diagram of the
LM5005 and a typical application board schematic for the
LM5005. In a buck regulator there are two loops where
currents are switched very fast. The first loop starts from the
input capacitors, to the regulator VIN pin, to the regulator SW
pin, to the inductor then out to the load. The second loop
starts from the output capacitor ground, to the regulator
PGND pins, to the regulator IS pins, to the diode anode, to
the inductor and then out to the load. Minimizing the loop
area of these two loops reduces the stray inductance and
minimizes noise and possible erratic operation. A ground
plane in the PC board is recommended as a means to
connect the input filter capacitors to the output filter capaci-
tors and the PGND pins of the regulator. Connect all of the
low power ground connections (C
the regulator AGND pin. Connect the AGND and PGND pins
5V, 2.5A Demo Board Bill of Materials
C
C
C
C
C
C
C
C
C
C
C
C
D
R
R
R
R
R
R
R
U
L
ITEM
10
11
12
1
2
3
4
5
6
7
8
9
1
1
1
2
3
4
5
6
7
1
C4532X7R2A225M
C4532X7R2A225M
C0805C331G1GAC
C2012X7R2A103K
C2012X7R2A103K
OPEN
C2012X7R2A223K
C2012X7R1C474M
C3225X7R1C226M
EEFHE0J151R
C0805C331G1GAC
OPEN
CSHD6-100C
6CWQ10FN
DR127-330
OPEN
OPEN
CRCW12062102F
CRCW12064992F
CRCW12065111F
CRCW12061651F
CRCW2512100J
LM5005
PART NUMBER
SS
, R
T
, C
(Continued)
RAMP
) directly to
CAPACITOR, CER, TDK
CAPACITOR, CER, TDK
CAPACITOR, CER, KEMET
CAPACITOR, CER, TDK
CAPACITOR, CER, TDK
NOT USED
CAPACITOR, CER, TDK
CAPACITOR, CER, TDK
CAPACITOR, CER, TDK
CAPACITOR, SP, PANASINIC
CAPACITOR, CER, KEMET
NOT USED
DIODE, 100V, CENTRAL
DIODE, 100V, IR (D1-ALT)
INDUCTOR, COOPER
NOT USED
NOT USED
RESISTOR
RESISTOR
RESISTOR
RESISTOR
RESISTOR
REGULATOR, NATIONAL SEMICONDUCTOR
19
together through the topside copper area covering the entire
underside of the device. Place several vias in this underside
copper area to the ground plane.
The two highest power dissipating components are the re-
circulating diode and the LM5005 regulator IC. The easiest
method to determine the power dissipated within the
LM5005 is to measure the total conversion losses (Pin –
Pout) then subtract the power losses in the Schottky diode,
output inductor and snubber resistor. An approximation for
the Schottky diode loss is P = (1-D) x Iout x Vfwd. An
approximation for the output inductor power is P = I
x 1.1, where R is the DC resistance of the inductor and the
1.1 factor is an approximation for the ac losses. If a snubber
is used, the power loss can be estimated with an oscillo-
scope by observation of the resistor voltage drop at both
turn-on and turn-off transitions. The regulator has an ex-
posed thermal pad to aid power dissipation. Adding several
vias under the device to the ground plane will greatly reduce
the regulator junction temperature. Selecting a diode with an
exposed pad will aid the power dissipation of the diode.
DESCRIPTION
0.022µ, 100V
0.01µ, 100V
0.01µ, 100V
330p, 100V
330p, 100V
2.2µ, 100V
2.2µ, 100V
0.47µ, 16V
150µ, 6.3V
22µ, 16V
VALUE
10, 1W
49.9K
5.11K
1.65K
33µH
21K
www.national.com
OUT
2
x R