iru3065 International Rectifier Corp., iru3065 Datasheet - Page 6

• Manufacturer Part Number: iru3065
• Description: Positive To Negative Dc To Dc Controller
• Manufacturer: International Rectifier Corp.

IRU3065(PbF)
in figure 1. The schottky diode can be replaced with a
100 resistor (Figure 28.) with a small sacrifice of effi-
ciency but lower cost.
Thermal Consideration
The thermal design is to ensure maximum junction tem-
perature of IRU3065 will not exceed the maximum op-
eration junction temperature, which is 125 C. The junc-
tion temperature can be estimated by the following:
T
Where
case which is usually provided in the specification. P
is the power dissipation. T
The package thermal resistance of IRU3065 is estimated
as 230C/W due to compact package.
is 70C, the maximum power dissipation of IRU3065 will
be
For High Power Application
current applications. Figure 4. shows the rise time ver-
sus cap load. For big capacitor load, the rise time is
increasing.
Fig.4. Rise time versus cap load.
load current up to 1A. For higher power applications,
external driver is recommended to driver the external
FETs.
6
The IR3065 driver is designed to driver PMOS for low
Assuming the maximum allowed ambient temperature
J
The internal gate driver of IRU3065 is designed for
= P
P
D
D
<(125-70C)/
90
80
70
60
50
40
30
20
10
0
0
JA
JA
is the thermal resistance from junction to
+T
Rise time versus cap load
0.5
A
T
J(MAX)
JA
=(125-70)/230=240mW
1
Cap(nF)
= 125 C
A
is the ambient temperature.
1.5
2
2.5
www.irf.com
D
Demo board Evaluation Results
Fig.1 shows the evaluation board schematic and the
selected components. The diode D1 can be replaced
with a 100ohm resistor. The measured efficiency ver-
sus load current is shown in Fig. 6. With the boot strap
schottky diode, the efficiency is slight higher compar-
ing with using 100ohm resistor.
quency should be selected. Figure. 5 shows a effi-
ciency curve when 4.7uH inductor is chosen. The maxi-
mum operation frequency reduces from 800k to 250kHz.
As a results, efficiency is more than 10% higher.
sured output voltage versus output current is shown in
Figure 7. When the load current approaches 400mA,
the output voltage starts to drop and goes into power
limit mode. When output is about 1A, the output voltage
will goes almost zero.
ure 8. The highest switching frequency occurs at about
440mA. As load current goes up, the IC goes into
power limit mode and frequency automatically goes down
to protect the system.
sus VCC is shown in Figure. 9. Since this threshold is
only a divided voltage of VCC, it will changes when
VCC changes. This should be aware in the application.
ure 11. Since the voltage reference is set by Vin. When
Vin changes, the output voltage will change along Vin.
Sometimes this feature is preferrable since Vout may
want to be tracked with Vin except the polarity. How-
ever, if more accurate output is required, a external
voltage reference should set the output voltage.
age waveforms are listed in Figure 13-17. Figure 15
shows the measured inductor voltage waveform when
output current is 250mA, which the converter is oper-
ated in regulation mode and output voltage is regulated
at desired voltage -5V. Figure 16 shows the measured
inductor voltage waveform when the output current is
equal to the critical current I
measured inductor voltage waveform when the output is
in short circuit, which indicates that the converter is in
power limit mode and output voltage is near zero.
.
For the evaluation board, the measured inductor volt-
For the application circuit shown in Fig.1. The mea-
The current sensing comparator threshold voltage ver-
The measured frequency versus load is listed in Fig-
If higher efficiency is preferred, lower operation fre-
The output voltage versus Vin=VCC is shown in fig-
OCP
. Figure 17 shows the