IR3865MTRPBF International Rectifier, IR3865MTRPBF Datasheet - Page 13

• Manufacturer Part Number: IR3865MTRPBF
• Description: IC BUCK SYNC ADJ 10A PQFN
• Manufacturer: International Rectifier
• Series: SupIRBuck™r
• Type: Step-Down (Buck), PWMr

Specifications of IR3865MTRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.5 V ~ 12 V
• Current - Output: 10A
• Frequency - Switching: Up to 750kHz
• Voltage - Input: 3 V ~ 21 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: *
• Package / Case: *
• Primary Input Voltage: 21V
• No. Of Outputs: 1
• Output Voltage: 12V
• Output Current: 10A
• No. Of Pins: 17
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 3 - 168 Hours
• Rohs Compliant: Yes
• Leaded Process Compatible: Yes
• Part Status: Preferred
• Package: PQFN / 4 x 5
• Circuit: Single Output
• Iout (a): 10
• Switch Freq (khz): 0 - 750
• Input Range (v): 3.0 - 21
• Output Range (v): 0.5 - 12
• Ocp Otp Uvlo Pre-bias Soft Start And: Constant On-Time + PGOOD + EN + Temp Comp OCP
• Digital Home Media: Yes
• Mobile Computing: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

CIRCUIT DESCRIPTION
GATE DRIVE LOGIC
The gate drive logic features adaptive dead
time, diode emulation, and a minimum lower
gate interval.
An
simultaneous conduction of the upper and lower
MOSFETs. The lower gate voltage must be
below approximately 1V after PWM goes HIGH
before the upper MOSFET can be gated on.
Also, the differential voltage between the upper
gate and PHASE must be below approximately
1V after PWM goes LOW before the lower
MOSFET can be gated on. The upper MOSFET
is gated on after the adaptive delay for PWM =
HIGH and the lower MOSFET is gated on after
the adaptive delay for PWM = LOW.
Selection of components for the converter is an
iterative process which involves meeting the
specifications
performance and cost. The following sections
will guide one through the process.
Inductor Selection
Inductor selection involves meeting the steady
state output ripple requirement, minimizing the
switching loss of the upper MOSFET, meeting
transient
minimizing the output capacitance. The output
voltage includes a DC voltage and a small AC
ripple component due to the low pass filter
which has incomplete attenuation of the
switching harmonics. Neglecting the inductance
in series with the output capacitor, the
magnitude
determined by the total inductor ripple current
flowing through the total equivalent series
resistance (ESR) of the output capacitor bank.
ΔI
COMPONENT SELECTION
2/16/2011 Rev2.3

T
adaptive
ON


V
2
response
of
IN

L

V
the
dead
and
OUT

AC
(5)
time
tradeoffs
specifications
voltage
prevents
ripple
between
and
the
is
One can use equation 5 to find the required
inductance. ΔI is defined as shown in Figure 24.
The main advantage of small inductance is
increased inductor current slew rate during a
load transient, which leads to a smaller output
capacitance requirement as discussed in the
Output Capacitor Selection section. The draw
back of using smaller inductances is increased
switching power loss in the upper MOSFET,
which reduces the system efficiency and
increases the thermal dissipation.
When FCCM = LOW, the lower MOSFET is
driven ‘off’ when the ZCROSS signal indicates
that the inductor current is about to reverse
direction. The ZCROSS comparator monitors
the PHASE voltage to determine when to turn
off the lower MOSFET. The lower MOSFET
stays ‘off’ until the next PWM falling edge.
When the lower peak of the inductor current is
above zero, IR3865 operates in continuous
conduction mode. The continuous conduction
mode can also be selected for all load current
levels by pulling FCCM to HIGH.
Whenever the upper MOSFET is turned ‘off’, it
stays ‘off’ for the Min Off Time denoted in the
Electrical
duration allows time to recharge the bootstrap
capacitor and allows the over current monitor
to sample the PHASE voltage.
Figure 24. Typical Input Current Waveform
Specifications.
IR3865MBF
This
minimum
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