UCD7100
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SLUS651C –MARCH 2005–REVISED MAY 2010
Thermal Information
The useful range of a driver is greatly affected by the drive power requirements of the load and the thermal
characteristics of the device package. In order for a power driver to be useful over a particular temperature range
the package must allow for the efficient removal of the heat produced while keeping the junction temperature
within rated limits. The UCD7K family of drivers is available in PowerPAD™ TSSOP package to cover a range of
application requirements. Both have the exposed pads to relieve thermal dissipation from the semiconductor
junction.
As illustrated in Reference [2], the PowerPAD™ packages offer a leadframe die pad that is exposed at the base
of the package. This pad is soldered to the copper on the PC board (PCB) directly underneath the device
package, reducing the ΘJC down to 4.7°C/W. The PC board must be designed with thermal lands and thermal
vias to complete the heat removal subsystem, as summarized in Reference [3].
Note that the PowerPAD™ is not directly connected to any leads of the package. However, it is electrically and
thermally connected to the substrate which is the ground of the device.
Circuit Layout Recommendations
In a power driver operating at high frequency, it is a significant challenge to get clean waveforms without much
overshoot/undershoot and ringing. The low output impedance of these drivers produces waveforms with high
di/dt. This tends to induce ringing in the parasitic inductances. Utmost care must be used in the circuit layout. It is
advantageous to connect the driver IC as close as possible to the leads. The driver device layout has the analog
ground on the opposite side of the output, so the ground should be connected to the bypass capacitors and the
load with copper trace as wide as possible. These connections should also be made with a small enclosed loop
area to minimize the inductance.
VIN
VOUT
Bias Supply
Bias
Winding
UCD7100PWP
1 VDD
14
13
PVDD
PVDD
VDS
3 3V3
IN
2
4
UCD91xx
with
CLA
1
2
AGND
VDS
OUT 12
OUT 11
Peripheral
CLF
5
CS
FB
6
7
ILIM
NC
PGND
PGND
10
9
2
8
CS
CS
COMMUNICATION
(Programming & Status Reporting)
2
Isolation
Amplifier
Figure 2. Isolated Forward Converter
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