IP1827TRPBF International Rectifier, IP1827TRPBF Datasheet - Page 21

• Manufacturer Part Number: IP1827TRPBF
• Description: IC DC-DC REG SYNC BUCK LGA
• Manufacturer: International Rectifier
• Series: iPOWIR™r
• Type: Step-Down (Buck), PWM - Voltage Moder

Specifications of IP1827TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 V ~ 12 V
• Current - Output: 25A
• Frequency - Switching: 225kHz ~ 1.65MHz
• Voltage - Input: 1.5 V ~ 16 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: *
• Package / Case: *
• Package: LGA - 7.7 x 7.7
• Circuit: Single Output
• Iout (a): 25
• Switch Freq (khz): 250 - 1500
• Input Range (v): 1.5 - 16
• Output Range (v): 0.6 - 0.75*Vin
• Internal Bias Ldo: Yes
• Ocp Otp Uvlo Pre-bias Soft Start And: Remote Sense + Body Tracking + Temp Comp OCP
• Pbf: PbF Option Available
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

OUTPUT CAPACITOR SELECTION
The voltage ripple and transient requirements determine
the output capacitors type and values. The criteria are
normally based on the value of the Effective Series
Resistance (ESR). However the actual capacitance value
and the Equivalent Series Inductance (ESL) are other
contributing components. These components can be
described as:
Since the output capacitor has a major role in the overall
performance of the converter and determines the result of
transient response, selection of the capacitor is critical.
The iP1827 can perform well with all types of capacitors.
As a rule, the capacitor must have low enough ESR to meet
output ripple and load transient requirements.
The goal for this design is to meet the voltage ripple
requirement in the smallest possible capacitor size.
Therefore it is advisable to select ceramic capacitors due
to their low ESR and ESL and small size. Fifteen of the
Panasonic ECJ‐2FB0J226ML (22uF, 6.3V, 3mOhm)
capacitors are a good choice.
FEEDBACK COMPENSATION
The iP1827 is a voltage mode controller. The control loop is
a single voltage feedback path including error amplifier
and error comparator. To achieve fast transient response
and accurate output regulation, a compensation circuit is
necessary. The goal of the compensation network is to
provide an open‐loop transfer function with the highest
0 dB crossing frequency and adequate phase margin
(greater than 45

ΔV
ΔI
V
o

L

0
V
= Inductor Ripple Current
= Output Voltage Ripple

o

21

(
V
ESL
V
V
o
o
o
(
)
o
(
ESR
(
ESR
C
).

)
)
)



January 24, 2011 | V1.2



V
8
in


*
L

V
I
C

L
o
V
(
o
*
I
ESL
o
L
*
ESR



)
F
*

s
ESL

V
o
(
C
)
Highly Integrated 25A Single‐input Voltage,
(15)
Synchronous Buck Regulator
The output LC filter introduces a double pole, ‐40dB/
decade gain slope above its corner resonant frequency,
and a total phase lag of 180
frequency of the LC filter is expressed as follows:
Figure 17 shows gain and phase of the LC filter. Since we
already have 180
the system runs the risk of being unstable.
The iP1827 uses a voltage‐type error amplifier with
high‐gain (110dB) and wide‐bandwidth. The output of
the amplifier is available for DC gain control and AC phase
compensation.
The error amplifier can be compensated either in type II
or type III compensation.
Local feedback with Type II compensation is shown in
Figure 18.
This method requires that the output capacitor should
have enough ESR to satisfy stability requirements.
In general the output capacitor’s ESR generates a zero
typically at 5kHz to 50kHz which is essential for an
acceptable phase margin.
The ESR zero of the output capacitor is expressed as
follows:
0dB
Gain
F
F
LC
ESR

F
LC
Figure 17: Gain and Phase of LC filter

2
2

o

-40dB/decade

phase shift from the output filter alone,

Frequency
*ESR*C
1
L
1
o

C
o
o
(see Figure 16). The resonant
o
-180°
0dB
-90°
Phase
0°
F
iP1827
LC
(17)
(16)
Frequency
97599