IR3865MTRPBF International Rectifier, IR3865MTRPBF Datasheet - Page 15

• 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

COMPONENT SELECTION
The
depends on the characteristic of the output
capacitor. V
series inductance (ESL) of the output capacitor
times the rate of change of the output current
and the ESR times the change of the output
current.
VESR is usually much greater than VESL. The
IR3865 requires a total ESR such that the ripple
voltage at the FB pin is greater than 7mV. The
second purpose of the output capacitor is to
minimize the overshoot of the output voltage
when the load decreases as shown in Figure
26. By using the law of energy before and after
the load removal, equation 8 shows the output
capacitance requirement for a load step down.
C
2/16/2011 Rev2.3
OUT
Figure 26. Typical Output Voltage Response
output

V
OS
DROP
L
voltage
2

I

STEP
is the sum of the equivalent
V
Waveform
OUT
2
drop,
2
(8)
V
DROP
,
initially
C
Boot Capacitor Selection
The boot capacitor starts the cycle fully charged
to a voltage of VB(0).
IR3865. Choose a sufficiently small ΔV such that
VB(0)-ΔV exceeds the maximum gate threshold
voltage to turn on the upper MOSFET.
Choose a boot capacitor value larger than the
calculated C
based on charge balance at CCM operation.
Usually the boot capacitor will be discharged to a
much lower voltage when the circuit is operating
in DCM mode at light load, due to much longer
lower MOSFET off time and the bias current
drawn by the IC. Boot capacitance needs to be
increased if insufficient turn-on of the upper
MOSFET is observed at light load, typically
larger than 0.1µF is needed. The voltage rating
of this part needs to be larger than VB(0) plus
the desired derating voltage. Its ESR and ESL
needs to be low in order to allow it to deliver the
large current and di/dt’s which drive MOSFETs
most efficiently. In support of these requirements
a ceramic capacitor should be chosen.
BOOT

C
g

BOOT



V
ΔV
B
(0)
in equation 9. Equation 9 is

1



Cg equals 0.6nF in
IR3865MBF
(9)
15