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ISL9120 Datasheet(PDF) 10 Page - Renesas Technology Corp

Part No. ISL9120
Description  Compact High Efficiency Low Power Buck-Boost Regulator
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Maker  RENESAS [Renesas Technology Corp]
Homepage  http://www.renesas.com
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ISL9120 Datasheet(HTML) 10 Page - Renesas Technology Corp

 
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ISL9120
FN8659 Rev.2.00
Page 10 of 13
May 23, 2017
Automatic Bypass Mode Operation
When the output voltage is close to the input voltage, generally
within 1% to 2%, the ISL9120 will engage automatic bypass
mode operation, which produces a direct connection between
the VIN and VOUT pins. This behavior provides excellent efficiency
and very low output voltage ripple.
Forced Bypass Mode Operation
Forced bypass mode operation is intended for applications where
the output regulation is not important but the device quiescent
current consumption is important. One example is when the
buck-boost regulator is providing power to an LDO and the LDO is
in standby mode with near zero output current. Under this
condition, putting the buck-boost regulator in bypass mode will
have essentially no impact on the LDO but save the 41µA
quiescent current consumption on the buck-boost regulator.
Because the bypass mode is an extreme power saving mode,
there is no overcurrent protection. Therefore, caution must be
taken not to overload or short-circuit the device. Power-up at
bypass mode is not recommended.
Output Voltage Programming
The ISL9120 is available in fixed and adjustable output voltage
versions. To use the fixed output version (ISL9120IINZ), the VOUT
pin must be connected directly to the FB pin.
In the adjustable output voltage version (ISL9120IIAZ), an
external resistor divider is required to program the output
voltage.
Applications Information
Component Selection
The fixed-output version of the ISL9120 requires only three
external power components to implement the buck-boost
converter: an inductor, an input capacitor, and an output
capacitor.
The adjustable ISL9120 versions require three additional
components to program the output voltage. Two external
resistors program the output voltage and a small capacitor is
added to improve transient response.
Output Voltage Programming, Adjustable
Version
Setting and controlling the output voltage of the ISL9120IIAZ
(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:
When designing a PCB, include a GND guard band around the FB
resistor network to reduce noise and improve accuracy and
stability. Resistors R1 and R2 should be positioned close to the
FB pin. The suggested value of the R1 resistor is 187k.
Feed-Forward Capacitor Selection
A small capacitor (C4 in Figure 17) in parallel with resistor R1 is
required to provide the specified load and line regulation. The
suggested value of this capacitor is 22pF for R1 =187k. An NPO
type capacitor is recommended.
Non-Adjustable Version FB Pin Connection
The fixed output versions of the ISL9120 do not require external
resistors or a capacitor on the FB pin. Simply connect VOUT to FB,
as shown in Figure 18.
FIGURE 17. TYPICAL ISL9120IIAZ APPLICATION
VOUT = 3.3V
VOUT
FB
C2
47
F
R1
R2
187k
60.4k
VIN
VIN =
1.8V TO 5.5V
EN
BYP
C1
10
F
ISL9120IIAZ
GND PGND
LX1
LX2
L1
1
H
C4
22pF
FORCED BYPASS
BUCK-BOOST
ENABLE
DISABLE


VOUT
0.8V
1
R1
R2
-------
+



=
(EQ. 1)
FIGURE 18. TYPICAL ISL9120IINZ APPLICATION
VOUT = 3.3V
VOUT
FB
C2
47
F
VIN
VIN =
1.8V TO 5.5V
C1
10
F
ISL9120IINZ
GND PGND
LX1
LX2
L1
1
H
EN
BYP
FORCED BYPASS
BUCK-BOOST
ENABLE
DISABLE


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