IRDC3710-QFN International Rectifier, IRDC3710-QFN Datasheet - Page 12

• Manufacturer Part Number: IRDC3710-QFN
• Description: BOARD EVAL SYNC BUCK CONTROLLER
• Manufacturer: International Rectifier

Specifications of IRDC3710-QFN

• Lead Free Status / Rohs Status: Supplier Unconfirmed

CHARGE PUMP
The purpose of the charge pump is to improve the
system efficiency. A combination of VCC, V5 and
three(3) external components are used to boost
PVCC up to V
MOSFET and reduces the R
a regular 5V rail driver. The lower R
conduction power loss as discussed in the Power
Loss section.
The charge pump is continuously enabled for FCCM
= HIGH. The charge pump circuit is disabled when
FCCM = LOW and the output loading is less than half
of inductor current ripple. In this case, PVCC is two
(2) diode voltage away from V5 rail. Therefore, the
power loss for driver is reduced. The charge pump
circuit stops switching the CPO pin for PVCC above
V
It is not recommended to use PVCC for supply power
to boot capacitor when use charge pump circuit. This
can be exceeding the maximum rating of BOOT to
PHASE pins and damages to the IC.
POWER UP SEQUENCE
With EN pin HIGH, IR3710 initiates a soft start when
the VCC and PVCC are in the above ULVO threshold
and V
and V
COMPONENT SELECTION
Selection of components for the converter is an
iterative process which involves meeting the
specifications and trade-offs between the
performance and cost. The following sections will
guide one through the process.
Power Loss
The main sources contributing to the power loss of a
converter are switching loss of the upper MOSFETs,
conduction loss of the lower MOSFETs, AC and DC
losses in the inductor, and driving loss which is a
large factor at light load condition.
In small duty cycle converter system, switching loss
is main power loss of upper MOSFETs because its
on-time is relatively small. To find the switching
power loss, Figure 19 shows the typical turn-on
waveform of the upper MOSFETs. Turn-off is
quantitatively similar with x-axis reversed. The
switching loss can be estimate as the cross sectional
area in the figure. Equation 4 and 5 show the
relationship of MOSFET’s switching charge and loss.
Page 12 of 20
CP TH
.
IN
IN
is in normal range. The order of VCC, PVCC
is not require.
CP TH
. PVCC drives the synchronous
DSON
www.irf.com
when compared to
DSON
reduces the
IR Confidential
Fs is the switching frequency. I
current. To find the driver current, Figure 20 shows
the simplified circuit of driver and MOSFET. I
be found by using Ohm’s law as shown in the
equation 6 with an assumption that V
voltage during t
switching power loss of a cycle can be easily be
found as shown in equation 7.
The reverse recovery power loss of the lower
MOSFETs is also a factor of the upper MOSFET’s
P
P
I
I
W
GDr(on
GDr(off
SW
SW
V
Driver
ON
Figure 20. Simplify Driver and MOSFET Circuit.
GS(th)
=
=
=
W
Figure 19. Typical Turn-On Waveform.
R
-
V
V
-
R
time)
time)
IN
IN
ON
PU
PD
⋅
⋅
⋅
Q
2
I
2
I
I
F
Gdr
=
PK
PK
V
=
GS1
S
DR
R
2
R
=
V
V
t
and t
PU
PD
1
DR
V
IN
R
⋅
(
IN
t3
Q
Q
+
V
IR3710MTRPBF
EXT
+
I
-
GS2
R
Qgd
GS2
GDr(on
⋅
3
R
-
2
. Therefore, the turn on
V
I
EXT
t1
EXT
PK
Qgd
)
t
+
C
C
(4)
2
R
I
+
+
PK
GD
GS
Q
-
G
R
R
Q
time)
⋅
GD
G
G
Q
GD
GDr
GS2
I
V
(6a)
OUT
MOSFET
(6b)
Qgd
is gate driver
⋅
I
t
F
GDr
+
3
Qgd
S
Q
(7)
GD
is the gate
4/26/10
V
Gdr
GS
⋅
C
F
can
DS
t
S
(5)