IR3856MTRPBF International Rectifier, IR3856MTRPBF Datasheet - Page 12

• Manufacturer Part Number: IR3856MTRPBF
• Description: IC BUCK SYNC ADJ 6A 17PQFN
• Manufacturer: International Rectifier
• Series: SupIRBuck™r
• Type: Step-Down (Buck)r

Specifications of IR3856MTRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.7 ~ 18.9 V
• Current - Output: 6A
• Frequency - Switching: 250kHz ~ 1.5MHz
• Voltage - Input: 1.5 ~ 21 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 17-PowerVQFN
• Power - Output: 1.11W
• Primary Input Voltage: 21V
• No. Of Outputs: 1
• Output Voltage: 18.9V
• 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): 250 - 1500
• Input Range (v): 1.5 - 21
• Output Range (v): 0.7 - 0.9*Vin
• Ocp Otp Uvlo Pre-bias Soft Start And: PGOOD + EN + SEQ + OVP + SYNC
• Design Tool: Yes
• Server Storage: Yes
• Routers Switches: Yes
• Base Station Telecom: Yes
• Digital Home Media: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Circuit Description
THEORY OF OPERATION
Introduction
The IR3856 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
250kHz to 1.5MHz and provides the capability of
optimizing the design in terms of size and
performance.
IR3856 provides precisely regulated output
voltage programmed via two external resistors
from 0.7V to 0.9*Vin.
The IR3856 operates with an external bias
supply from 4.5V to 5.5V, allowing an extended
operating input voltage range from 1.5V to 21V.
The device utilizes the on-resistance of the low
side MOSFET as current sense element, this
method enhances the converter’s efficiency and
reduces cost by eliminating the need for external
current sense resistor
IR3856 includes two low R
IR’s HEXFET technology. These are specifically
designed for high efficiency applications.
Under-Voltage Lockout and POR
The under-voltage lockout circuit monitors the
input supply Vcc 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 and Enable rise above their
thresholds.
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 IR3856 will turn on
only when the voltage at the Enable pin exceeds
this threshold, typically, 1.2V.
Rev2.0
.
ds(on)
MOSFETs using
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 IR3856 does not
turn on until the bus voltage reaches the desired
level. Only after the bus voltage reaches or
exceeds this level will the voltage at Enable pin
exceed its threshold, thus enabling the IR3856.
Therefore, in addition to being a logic input pin to
enable the IR3856, the Enable feature, with its
precise threshold, also allows the user to
implement an Under-Voltage Lockout for the bus
voltage V
output voltage applications, where we might want
the IR3856 to be disabled at least until V
exceeds the desired output voltage level.
Figure 3b. shows the recommended start-up
sequence for the non-sequenced operation of
IR3856, when Enable is used as a logic input.
Fig. 3b. Recommended startup sequence,
Fig. 3a. Normal Start up, Device turns on
when the Bus voltage reaches 10.2V
in
Non-Sequenced operation
. This is desirable particularly for high
IR3856MPbF
PD-97528
12
in