IR3821MTRPBF International Rectifier, IR3821MTRPBF Datasheet - Page 11
![IC REG SYNC BUCK 7A 5X6 15QFN](/photos/7/56/75611/15-powervqfn_sml.jpg)
IR3821MTRPBF
Manufacturer Part Number
IR3821MTRPBF
Description
IC REG SYNC BUCK 7A 5X6 15QFN
Manufacturer
International Rectifier
Series
SupIRBuck™r
Type
Step-Down (Buck)r
Datasheet
1.IR3821MTRPBF.pdf
(21 pages)
Specifications of IR3821MTRPBF
Internal Switch(s)
Yes
Synchronous Rectifier
Yes
Number Of Outputs
1
Voltage - Output
0.6 ~ 12 V
Current - Output
7A
Frequency - Switching
600kHz
Voltage - Input
2.5 ~ 21 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
15-PowerVQFN
Power - Output
2.1W
Part Status
Active
Package
PQFN / 5 x 6
Circuit
Single Output
Iout (a)
7
Switch Freq (khz)
600
Input Range (v)
2.5 - 21
Output Range (v)
0.6 - 12
Ocp Otp Uvlo Pre-bias Soft Start And
PGOOD
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Other names
IR3821MTRPBFTR
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
IR3821MTRPBF
Manufacturer:
SEIKOEPSON
Quantity:
2 611
Fig. 10: Typical application of the IR3821 for
Application Information
Design Example:
The following example is a typical application for
the IR3821. The application circuit is shown in
page 17.
Output Voltage Programming
Output voltage is programmed by reference
voltage and external voltage divider. The Fb pin
is the inverting input of the error amplifier, which
is internally referenced to 0.6V. The divider is
ratioed to provide 0.6V at the Fb pin when the
output is at its desired value. The output voltage
is defined by using the following equation:
When an external resistor divider is connected to
the output as shown in figure 10.
Equation (4) can be rewritten as:
For the calculated values of R
feedback compensation section.
11/04/08
V
V
I
R
F
ΔV
o
9
in
o
s
=
=
=
=
=
o
R
7
1
8
600
12
≤
programming the output voltage
∗
8 .
A
IR3624
V
IR3821
⎛
⎜ ⎜
⎝
o
30
V
V,(
V
=
V
O
kHz
V
−
ref
V
mV
ref
13
ref
∗
⎞
⎟ ⎟
⎠
Fb
⎛
⎜ ⎜
⎝
1
2 .
+
V,
--(
R
R
8
9
) 5
max
⎞
⎟ ⎟
⎠
--(
V
) 4
)
OUT
8
R
R
8
9
and R
9
see
Soft-Start Programming
The soft-start timing can be programmed by
selecting the soft-start capacitance value. The
start-up time of the converter can be calculated
by using:
Where T
For a start-up time of 11ms, the soft-start
capacitor will be 0.22uF.
Vc supply for single input voltage
To drive the high-side switch, it is necessary to
supply a gate voltage at least 4V greater than the
bus voltage. This is achieved by using a charge
pump configuration as shown in figure 11. This
method is simple and inexpensive. The operation
of the circuit is as follows: when the lower
MOSFET is turned on, the capacitor
pulled down to ground and charges, up to V
value, through the diode (D1). The bus voltage
will be added to this voltage when upper
MOSFET turns on in next cycle, and providing
supply voltage (Vc) through diode (D2). Vc is
approximately:
Capacitors in the range of 0.1uF are generally
adequate for most applications. The diodes must
be a fast recovery device to minimize the amount
of charge fed back from the charge pump
capacitor into V
to block the full power rail voltage, which is seen
when the high-side MOSFET is switched on. For
low-voltage application, schottky diodes can be
used to minimize forward drop across the diodes
at start up.
Fig. 11: Charge pump circuit to generate
V
start
C
≅
is the desired start-up time (ms)
2
∗
C
V
SS
BUS
bus
≅
−
. The diodes need to be able
Vc voltage
20
(
V
D
μ
IR3821MPbF
1
A
+
*
V
T
D
start
2
)
--(
--(
) 6
PD-60331
) 1
(C1) is
BUS
11