IR3473MTRPBF International Rectifier, IR3473MTRPBF Datasheet - Page 15

• Manufacturer Part Number: IR3473MTRPBF
• Description: IC BUCK SYNC ADJ 6A PQFN
• Manufacturer: International Rectifier
• Series: SupIRBuck™r
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of IR3473MTRPBF

• 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 ~ 27 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: *
• Package / Case: *
• Primary Input Voltage: 27V
• No. Of Outputs: 1
• Output Voltage: 12V
• 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): 0 - 750
• Input Range (v): 3.0 - 27
• 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
• Industrial 24v Input: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Output Capacitor Selection
Selection of the output capacitor requires meeting
voltage overshoot requirements during load removal, and
meeting steady state output ripple voltage requirements.
The output 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 28. Equation 7 shows the charge
requirement for a certain load step. The advantage
provided by the IR3473 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 Specifications section.
The IR3473 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
reduced recovery time.
The output voltage drop, V
characteristic of the output capacitor. V
the equivalent 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.
Current
Figure 28: Charge Requirement during Load Step
Load
Q
C
OUT

C
15


V
Output
Charge
V
DROP

February 16, 2011 | ADVANCED DATASHEET | V1.9 | PD97601
1
ON
Δt
0.5
+ Min Off Time). This results in




1
2
DROP
Istep


L
V
, initially depends on the
Inductor

IN
 
ΔIstep
Rate
Slew

t
V
I
STEP
OUT
DROP
(7a)
2




is the sum of
(7b)
t
6A Highly Integrated SupIRBuck
VESR is usually much greater than VESL. The IR3473
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 29. By using the law of
energy before and after the load removal, equation 8
shows the output capacitance requirement for a load
step down.
Boot Capacitor Selection
The boot capacitor starts the cycle fully charged to a
voltage of VB(0). Cg equals 0.58nF in IR3473. 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
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. It’s 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
V
DROP
V
I
Figure 29: Typical Output Voltage Response Waveform
OUT
in equation 9. Equation 9 is based on charge balance
OUT
V
ESR
C
V
L
C
BOOT
OUT


C
V
g
OS
I
L

STEP



2

V
I

ΔV
STEP
B
TM
V
(0)
OUT
2
V

2
OS
1



(8)
(9)
IR3473