IR3897MTRPBF International Rectifier, IR3897MTRPBF Datasheet - Page 17

• Manufacturer Part Number: IR3897MTRPBF
• Description: 4A Highly Integrated Single-Input Voltage, Synchronous Buck Regulator in a PQFN package.
• Manufacturer: International Rectifier

Specifications of IR3897MTRPBF

• Part Status: Active and Preferred
• Package: PQFN / 4 x 5
• Circuit: Single Output
• Iout (a): 4
• Switch Freq (khz): 0 - 1500
• Input Range (v): 1.0 - 16
• Output Range (v): 0.5 - 12
• Pbf: PbF Option Available

THEORY OF OPERATION
DESCRIPTION
The IR3897 uses a PWM voltage mode control scheme with
external compensation to provide good noise immunity
and maximum flexibility in selecting inductor values and
capacitor types.
The switching frequency is programmable from 300kHz
to 1.5MHz and provides the capability of optimizing the
design in terms of size and performance.
IR3897 provides precisely regulated output voltage
programmed via two external resistors from 0.5V to
0.86*Vin.
The IR3897 operates with an internal bias supply (LDO)
which is connected to the Vcc/LDO_out pin. This allows
operation with single supply. The bias voltage is variable
according to load condition. If the output load current is
less than half of the peak‐to‐peak inductor current, a lower
bias voltage, 4.4V, is used as the internal gate drive
voltage; otherwise, a higher voltage, 6.4V, is used.
This feature helps the converter to reduce power losses.
The device can also be operated with an external supply
from 4.5 to 7.5V, allowing an extended operating input
voltage (PVin) range from 1.0V to 16V. For using the
internal LDO supply, the Vin pin should be connected to
PVin pin. If an external supply is used, it should be
connected to Vcc/LDO_Out pin and the Vin pin should be
shorted to Vcc/LDO_Out pin.
The device utilizes the on‐resistance of the low side
MOSFET (synchronous Mosfet) as current sense element.
This method enhances the converter’s efficiency and
reduces cost by eliminating the need for external current
sense resistor.
IR3897 includes two low R
technology. These are specifically designed for high
efficiency applications.
UNDER‐VOLTAGE LOCKOUT AND POR
The under‐voltage lockout circuit monitors the voltage of
Vcc/LDO_Out pin and the Enable input. It assures that the
MOSFET driver outputs remain in the off state whenever
either of these two signals drop below the set thresholds.
Normal operation resumes once Vcc/LDO_Out and Enable
rise above their thresholds.
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FEBRUARY 02, 2012 |DATA SHEET | Rev 3.2
ds(on)
MOSFETs using IR’s HEXFET
Single‐Input Voltage, Synchronous Buck Regulator
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4A Highly Integrated SupIRBuck
The POR (Power On Ready) signal is generated when all
these signals reach the valid logic level (see system block
diagram). When the POR is asserted the soft start
sequence starts (see soft start section).
ENABLE
The Enable features another level of flexibility for start up.
The Enable has precise threshold which is internally
monitored by Under‐Voltage Lockout (UVLO) circuit.
Therefore, the IR3897 will turn on only when the voltage
at the Enable pin exceeds this threshold, typically, 1.2V.
If the input to the Enable pin is derived from the bus
voltage by a suitably programmed resistive divider, it can
be ensured that the IR3897 does not turn on until the bus
voltage reaches the desired level (Fig. 4). Only after the bus
voltage reaches or exceeds this level and voltage at the
Enable pin exceeds its threshold, IR3897 will be enabled.
Therefore, in addition to being a logic input pin to enable
the IR3897, the Enable feature, with its precise threshold,
also allows the user to implement an Under‐Voltage
Lockout for the bus voltage (PVin). This is desirable
particularly for high output voltage applications, where we
might want the IR3897 to be disabled at least until PVIN
exceeds the desired output voltage level.
A resistor divider is used at EN pin from PVin to turn on the
device at 10.2V.
Enable Threshold = 1.2V
Figure 4: Normal Start up, device turns on
when the bus voltage reaches 10.2V
10. 2 V
TM
Pvin (12V)
IR3897
Vcc
Intl_SS
Enable
PD‐97663