en5322 Enpirion, en5322 Datasheet - Page 10

• Manufacturer Part Number: en5322
• Description: 2 A Voltage Mode Synchronous Buck Pwm Dc-dc Converter With Integrated Inductor
• Manufacturer: Enpirion

March 2008
features include under voltage lockout (UVLO),
over current protection, short circuit protection,
and thermal overload protection.
Stability over Wide Range of Operating
Conditions
The EN5322 utilizes an internal compensation
network and is designed to provide stable
operation over a wide range of operating
conditions. To improve transient performance
or reduce output voltage ripple with dynamic
loads
supplementary capacitance to the output. The
EN5322 is stable with up to 60 µF of output
capacitance without compensation adjustment.
Additional output capacitance above 60 µF can
be
adjustment depending on the application. The
high switching frequency allows for a wide
control loop bandwidth.
Soft Start
The internal soft start circuit limits inrush
current when the device starts up from a power
down condition or when the ENABLE pin is
asserted “high”. Digital control circuitry sets the
V
and inrush current to ensure a glitch-free start
up. The soft start ramp rate is nominally 1.5
V/ms.
Over Current/Short Circuit Protection
When an over current condition occurs, V
pulled low. This condition is maintained for a
period of 1.2 ms and then a normal soft start
cycle is initiated. If the over current condition
still persists, this cycle will repeat.
Under Voltage Lockout
An under voltage lockout circuit will hold off
switching during initial power up until the input
voltage reaches sufficient level to ensure
proper operation. If the voltage drops below the
UVLO threshold the lockout circuitry will again
disable switching. Hysteresis is included to
prevent chattering between UVLO high and low
states.
©Enpirion 2008 all rights reserved, E&OE
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Enable
The ENABLE pin provides means to shut down
the converter or initiate normal operation. A
logic high will enable the converter to go
through the soft start cycle and regulate the
output voltage to the desired value. A logic low
will allow the device to discharge the output
and go into shutdown mode for minimal power
consumption. When the output is discharged,
an auxiliary NFET turns on and limits the
discharge current to 300 mA or below. In
shutdown mode, the device typically drains
17µA.
floating.
Thermal Shutdown
When excessive power is dissipated in the
device, its junction temperature rises. Once the
junction temperature exceeds the thermal
shutdown temperature 155 °C, the thermal
shutdown circuit turns off the converter,
allowing the device to cool. When the junction
temperature drops 15 °C, the device will be re-
enabled and go through a normal startup
process.
Power OK
The EN5322 provides an open drain output to
indicate if the output voltage stays within 92%
to 111% of the set value. Within this range, the
POK output is allowed to be pulled high.
Outside
However, during transitions such as power up,
power down, and dynamic voltage scaling, the
POK output will not change state until the
transition is complete for enhanced noise
immunity.
The POK has 5 mA sink capability for events
where it needs to feed a digital controller with
standard CMOS inputs. When POK is pulled
high, the pin leakage current is as low as 500
nA maximum over temperature. This allows a
large pull up resistor such as 100 kΩ to be
used for minimal current consumption in
shutdown mode.
The POK output can also be conveniently used
as an ENABLE input of the next stage for
power sequencing of multiple converters.
The ENABLE pin must not be left
this
range,
POK
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remains
EN5322QI
low.