ISL91127IR Datasheet, PDF (10/12 Pages) Intersil Corporation – High Efficiency Buck-Boost Regulator with 4.5A Switches

ISL91127IR
ISL91127IRAZ
V_IN = 1.8V TO 5.5V _PVIN
C₁
LX1
10µF
LX2
VIN
EN
VOUT
MODE
FB
SGND PGND
L₁
1µH
V_OUT = 1V TO 5.2V
R₁
C₃
C2
2x22µF
R₂
FIGURE 20. ADJUSTABLE OUTPUT APPLICATION
Output Voltage Programming, Adjustable
Version
When VREF is connected to GND, setting and controlling the
output voltage of the ISL91127IRAZ (adjustable output version)
can be accomplished by selecting the external resistor values.
Equation 1 can be used to derive the R₁ and R₂ resistor values:
V_OUT
=
0.8
V




1
+
R^-R----12- _{}
(EQ. 1)
When designing a PCB, include a GND guard band around the
feedback resistor network to reduce noise and improve accuracy
and stability. Resistors R₁ and R₂ should be positioned close to
the FB pin.
Feed-Forward Capacitor Selection
A small capacitor (C₃ in Figure 20) in parallel with resistor R₁ is
required to provide the specified load and line regulation. The
suggested value of this capacitor is 56pF for R₁ = 1MΩ. An NPO
type capacitor is recommended.
Inductor Selection
An inductor with high frequency core material (e.g., ferrite core)
should be used to minimize core losses and provide good
efficiency. The inductor must be able to handle the peak
switching currents without saturating.
A 1µH inductor with ≥4A saturation current rating is
recommended. Select an inductor with low DCR to provide good
efficiency. In applications where radiated noise must be
minimized, a toroidal or shielded inductor can be used.
PVIN and V_OUT Capacitor Selection
The input and output capacitors should be ceramic X5R type with
low ESL and ESR. The recommended input capacitor value is
2x10µF. The recommended V_OUT capacitor value is 2x22µF.
TABLE 2. CAPACITOR VENDOR INFORMATION
MANUFACTURER
SERIES
WEBSITE
AVX
X5R
www.avx.com
Murata
X5R
www.murata.com
Taiyo Yuden
X5R
www.t-yuden.com
TDK
X5R
www.tdk.com
Recommended PCB Layout
Correct PCB layout is critical for proper operation of the
ISL91127IR. The input and output capacitors should be
positioned as closely to the IC as possible. The ground
connections of the input and output capacitors should be kept as
short as possible, and should be on the component layer to avoid
problems that are caused by high switching currents flowing
through PCB vias.
MANUFACTURER
Toko
Coilcraft
MFR. PART NUMBER
1277AS-H-1R0M
FDSD0312-H-1R0M
XFL4020-102ME
TABLE 3. INDUCTOR VENDOR INFORMATION
DESCRIPTION
DIMENSION (mm)
1µH, 20%, DCR = 34mΩ(typical),
I_SAT = 4.6A (typical)
1µH, 20%, DCR = 43mΩ(typical),
I_SAT = 4.5A (typical)
1µH, 20%, DCR = 11mΩ(typical),
I_SAT = 5.1A (typical)
3.2x2.5x1.2
3.2x3.0x1.2
4.0x4.0x2.1
WEBSITE
www.toko.com
www.coilcraft.com
Submit Document Feedback ₁₀
FN8859.1
August 3, 2016