EL7564CRE Intersil, EL7564CRE Datasheet - Page 15

• Manufacturer Part Number: EL7564CRE
• Description: IC REG 4A DC-DC STEP DN 28HTSSOP
• Manufacturer: Intersil
• Type: Step-Down (Buck)r

Specifications of EL7564CRE

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1 ~ 3.8 V
• Current - Output: 4A
• Frequency - Switching: 1MHz
• Voltage - Input: 4.5 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP Exposed Pad, 28-eTSSOP, 28-HTSSOP
• Power - Output: 13W
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

4. Start-up Delay
A capacitor can be added to the EN pin to delay the
converter start-up (Figure 26) by utilizing the pull-up current.
The delay time is approximately:
Thermal Management
The EL7564CM utilizes “fused lead” packaging technology in
conjunction with the system board layout to achieve a lower
thermal resistance than typically found in standard SO20
packages. By fusing (or connecting) multiple external leads
to the die substrate within the package, a very conductive
heat path is created to the outside of the package. This
conductive heat path MUST then be connected to a heat
sinking area on the PCB in order to dissipate heat out and
away from the device. The conductive paths for the
EL7564CM package are the fused leads: # 6, 7, 11, 12, and
13. If a sufficient amount of PCB metal area is connected to
the fused package leads, a junction-to-ambient resistance of
43°C/W can be achieved (compared to 85°C/W for a
standard SO20 package). The general relationship between
PCB heat-sinking metal area and the thermal resistance for
this package is shown in the Performance Curves section of
this data sheet. It can be readily seen that the thermal
resistance for this package approaches an asymptotic value
of approximately 43°C/W without any airflow, and 33°C/W
with 100 LFPM airflow. Additional information can be found
in Application Note #8 (Measuring the Thermal Resistance
of Power Surface-Mount Packages). For a thermal shutdown
die junction temperature of 135°C, and power dissipation of
1.5W, the ambient temperature can be as high as 70°C
without airflow. With 100 LFPM airflow, the ambient
temperature can be extended to 85°C.
t
d
(
ms
10
1
2
6
7
8
9
)
STN
STP
=
1200
EL7564
+
-
×
C µF
FIGURE 28. START-UP DELAY
(
20
19
15
14
13
12
11
)
15
C
V
OUT
t
d
TIME
V
V
IN
O
EL7564
The EL7564CRE utilizes the 28-pin HTSSOP package. The
majority of heat is dissipated through the heat pad exposed
at the bottom of the package. Therefore, the heat pad needs
to be soldered to the PCB. The thermal resistance for this
package is as low as 29°C/W, better than that of SO20.
Typical performance is shown in the curves section. The
actual junction temperature can be measured at V
Since the thermal performance of the IC is heavily
dependent on the board layout, the system designer should
exercise care during the design phase to ensure that the IC
will operate under the worst-case environmental conditions.
Layout Considerations
The layout is very important for the converter to function
properly. Power Ground (
be separated to ensure that the high pulse current in the
Power Ground never interferes with the sensitive signals
connected to Signal Ground. They should only be connected
at one point (normally at the negative side of either the input
or output capacitor.)
The trace connected to the FB pin is the most sensitive
trace. It needs to be as short as possible and in a “quiet”
place, preferably with the PGND or SGND traces
surrounding it.
In addition, the bypass capacitor connected to the V
needs to be as close to the pin as possible.
The heat of the chip is mainly dissipated through the PGND
pins for the CM package, and through the heat pad at the
bottom for the CRE package. Maximizing the copper area
around these PGND pins or the heat pad is preferable. In
addition, a solid ground plane is always helpful for the EMI
performance.
The demo board is a good example of layout based on these
principles. Please refer to the EL7564 Application Brief for
the layout.
) and Signal Ground (
TJ
May 9, 2005
) should
DD
pin.
FN7297.3
pin