IR3856MTRPBF International Rectifier, IR3856MTRPBF Datasheet - Page 14

• Manufacturer Part Number: IR3856MTRPBF
• Description: IC BUCK SYNC ADJ 6A 17PQFN
• Manufacturer: International Rectifier
• Series: SupIRBuck™r
• Type: Step-Down (Buck)r

Specifications of IR3856MTRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.7 ~ 18.9 V
• Current - Output: 6A
• Frequency - Switching: 250kHz ~ 1.5MHz
• Voltage - Input: 1.5 ~ 21 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 17-PowerVQFN
• Power - Output: 1.11W
• Primary Input Voltage: 21V
• No. Of Outputs: 1
• Output Voltage: 18.9V
• Output Current: 6A
• No. Of Pins: 17
• Operating Temperature Range: -40°C To +125°C
• Peak Reflow Compatible (260 C): Yes
• Rohs Compliant: Yes
• Leaded Process Compatible: Yes
• Part Status: Preferred
• Package: PQFN / 4 x 5
• Circuit: Single Output
• Iout (a): 6
• Switch Freq (khz): 250 - 1500
• Input Range (v): 1.5 - 21
• Output Range (v): 0.7 - 0.9*Vin
• Ocp Otp Uvlo Pre-bias Soft Start And: PGOOD + EN + SEQ + OVP + SYNC
• Design Tool: Yes
• Server Storage: Yes
• Routers Switches: Yes
• Base Station Telecom: Yes
• Digital Home Media: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Operating Frequency
The switching frequency can be programmed
between 250kHz – 1500kHz by connecting an
external resistor from R
tabulates the oscillator frequency versus R
Shutdown
The IR3856 can be shutdown by pulling the
Enable pin below its 1 V threshold. This will tri-
state both, the high side driver as well as the low
side driver. Alternatively, the output
shutdown by pulling the soft-start pin below 0.3V.
Normal operation is resumed by cycling the
voltage at the Soft Start pin.
Over-Current Protection
The over current protection is performed by
sensing current through the R
MOSFET. This method enhances the converter’s
efficiency and reduces cost by eliminating a
current sense resistor. As shown in figure 7, an
external resistor (R
OCSet pin and the switch node (SW) which sets
the current limit set point.
An internal current source sources current (I
) out of the OCSet pin. This current is a function
of Rt and hence, of the free-running switching
frequency.
Table 1. Switching Frequency and I
Rev2.0
R
R
47.5
47.5
35.7
35.7
28.7
28.7
23.7
23.7
20.5
20.5
17.8
17.8
15.8
15.8
14.3
14.3
12.7
12.7
11.5
11.5
10.7
10.7
9.76
9.76
9.31
9.31
t
t
(kΩ)
(kΩ)
External Resistor (R
F
F
300
300
400
400
500
500
600
600
700
700
800
800
900
900
1000
1000
1100
1100
1200
1200
1300
1300
1400
1400
1500
1500
s
s
OCSet
(kHz)
(kHz)
) is connected between
t
pin to Gnd. Table 1
DS(on)
t
)
I
I
29.4
29.4
39.2
39.2
48.7
48.7
59.07
59.07
68.2
68.2
78.6
78.6
88.6
88.6
97.9
97.9
110.2
110.2
121.7
121.7
130.8
130.8
143.4
143.4
150.3
150.3
ocset
ocset
OCSet
of low side
(μA)
(μA)
can be
t
vs.
.
OCSet
An over current is detected if the OCSet pin goes
below ground. Hence, at the current limit
threshold, V
setting I
The OCP circuit starts sampling current typically
160 ns after the low gate drive rises to about 3V.
This delay functions to filter out switching noise.
Table 1. shows I
frequencies.
develops a voltage across R
side MOSFET is turned on, the inductor current
flows through the Q2 and results in a voltage at
OCSet which is given by:
Fig. 7. Connection of over current sensing resistor
An
comparator, latches OCP signal and cycles the
soft start function in hiccup mode.
The hiccup is performed by shorting the soft-start
capacitor to ground and counting the number of
switching cycles. The Soft Start pin is held low
until 4096 cycles have been completed. The
OCP signal resets and the converter recovers.
After every soft start cycle, the converter stays in
this mode until the overload or short circuit is
removed.
V
OCSet
I
OCSet
R
overcurrent
OCSet
=
Limit
(
μA
(
I
OCSet
, R
)
=
OCset
=
R
OCSet
R
The
DS
∗
1400
t
=0. Then, for a current limit
R
(
(k
I
on
OCSet
OCSet
is calculated as follows:
Ω
detection
OCSet
)
)
*
internal
..........
IR3856MPbF
I
)
Limit
−
at different switching
(
R
OCSet
..........
..........
DS
trips
(on
current
. When the low
)
PD-97528
..........
..........
∗
I
L
the
)
..........
....
.....(
source
(4)
OCP
14
.(3)
) 2