IR3863MTR1PBF International Rectifier, IR3863MTR1PBF Datasheet - Page 14

• Manufacturer Part Number: IR3863MTR1PBF
• Description: IC BUCK SYNC ADJ 6A PQFN
• Manufacturer: International Rectifier
• Series: SupIRBuck™r
• Type: Step-Down (Buck), PWMr

Specifications of IR3863MTR1PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.5 V ~ 12 V
• Current - Output: 6A
• 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: 6A
• 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): 6
• 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
Input Capacitor Selection
The main function of the input capacitor bank is
to provide the input ripple current and fast slew
rate current during the load current step up. The
input capacitor bank must have adequate ripple
current carrying capability to handle the total
RMS current. Figure 24 shows a typical input
current. Equation 6 shows the RMS input
current. The RMS input current contains the DC
load current and the inductor ripple current. As
shown in equation 5, the inductor ripple current
is unrelated to the load current. The maximum
RMS input current occurs at the maximum
output current. The maximum power dissipation
in the input capacitor equals the square of the
maximum RMS input current times the input
capacitor’s total ESR.
The voltage rating of the input capacitor needs
to be greater than the maximum input voltage
because of high frequency ringing at the phase
node. The typical percentage is 25%.
I

IN_RMS
2/16/2011 Rev2.4
I
OUT


T
ON
Ts
1


Fs
Ts

0
f

2
 
1
t


dt
1
3




I
ΔI
OUT



2
(6)
Figure 25. Charge Requirement during Load Step
Output Capacitor Selection
Selection of the output capacitor requires
meeting voltage overshoot requirements during
load removal, and meeting steady state output
ripple voltage requirements.
capacitor is the most expensive converter
component and increases the overall system
cost. The output capacitor decoupling in the
converter typically includes the low frequency
capacitor, such as Specialty Polymer Aluminum,
and mid frequency ceramic capacitors.
The first purpose of output capacitors is to
provide current when the load demand exceeds
the inductor current, as shown in Figure 25.
Equation 7 shows the charge requirement for a
certain load step. The advantage provided by
the IR3863 at a load step is the reduced delay
compared to a fixed frequency control method.
If the load increases right after the PWM signal
goes low, the longest delay will be equal to the
minimum lower gate on-time as shown in the
Electrical Specification table. The IR3863 also
reduces the inductor current slew time, the time
it takes for the inductor current to reach equality
with the output current, by increasing the
switching frequency up to 1/(T
Time). This results in reduced recovery time.
Q
C
OUT

C


V
V
DROP

1
0.5




1
2
Istep


L
V

IN
 
ΔIstep

t
V
IR3863MBF
OUT
(7a)
2




ON
(7b)
The output
+ Min Off
14