IR3856MTRPBF International Rectifier, IR3856MTRPBF Datasheet - Page 18

• 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

Minimum on time Considerations
The minimum ON time is the shortest amount of
time for which the Control FET may be reliably
turned on, and this depends on the internal
timing delays. For the IR3856, the typical
minimum on-time is specified as 50 ns.
Any design or application using the IR3856 must
ensure operation with a pulse width that is higher
than this minimum on-time and preferably higher
than 100 ns. This is necessary for the circuit to
operate without jitter and pulse-skipping, which
can cause high inductor current ripple and high
output voltage ripple.
In any application that uses the IR3856, the
following condition must be satisfied:
The minimum output voltage is limited by the
reference voltage and hence V
Therefore, for V
Therefore, at the maximum recommended input
voltage 21V and minimum output voltage, the
converter should be designed at a switching
frequency that does not exceed 333 kHz.
Conversely, for operation at the maximum
recommended operating frequency 1.65 MHz
and minimum output voltage, any voltage above
4.2 V may not be stepped down without pulse-
skipping.
Rev2.0
∴
∴
∴
∴
V
V
t
in
on
V
in
t
on
t
×
(min)
in
×
on
F
(min)
F
×
s
out(min)
=
s
=
F
≤
≤
≤
V
s
F
D
≤
in
V
t
100
s
V
≤
0.7
on
t
out
V
on
out
×
= 0.7 V,
t
in
V
on
(min)
(min)
V
F
ns
V
out
×
out
(min)
s
F
=
s
7
×
10
out(min)
6
V/s
= 0.7 V.
Maximum Duty Ratio Considerations
A fixed off-time of 200 ns maximum is specified
for the IR3856. This provides an upper limit on
the operating duty ratio at any given switching
frequency. It is clear, that higher the switching
frequency, the lower is the maximum duty ratio at
which the IR3856 can operate. To allow a margin
of 50ns, the maximum operating duty ratio in any
application
accommodate about 250 ns off-time. Fig 10.
shows a plot of the maximum duty ratio v/s the
switching frequency, with 250 ns off-time.
Fig. 11. Maximum duty cycle v/s switching
95
90
85
80
75
70
65
60
55
250
frequency.
450
using
650
S w itchin g Freq uency (kH z )
M a x Duty Cycle
the
IR3856MPbF
850
IR3856
1050
PD-97528
1250
should
1450
18
still
1650