en5336 Enpirion, en5336 Datasheet - Page 7

• Manufacturer Part Number: en5336
• Description: 3a Voltage Mode Synchronous Buck Pwm Dc-dc Converter With Integrated Inductor External Output Voltage Programming
• Manufacturer: Enpirion

Rev 1.0 November 2006
Theory of Operation
Synchronous Buck Converter
The EN5336QI is a synchronous, programmable
power supply with integrated power MOSFET
switches and integrated inductor. The nominal
input voltage range is 2.4-5.5V. The output
voltage is programmed using an external resistor
divider network. The feedback control loop is a
voltage-mode
compensation network. The part uses a low-
noise PWM topology. Up to 3A of continuous
output current can be drawn from this converter.
The 5MHz operating frequency enables the use
of small-size input and output capacitors, and a
wide controller bandwidth.
The power supply has the following protection
features:
Additional features include:
Power good circuit indicating whether the output
voltage is within 90% and the programmed OVP
trip-point percentage of the programmed voltage.
Device Programming Options
The EN5336QI output voltage is programmed
using a simple resistor divider network. Figure 4
shows the resistor divider configuration.
The EN5336QI output voltage and over voltage
thresholds are determined by the voltages
presented at the XFB and XOV pins respectively.
These voltages are set by way of resistor dividers
between V
to XFB and XOV.
©Enpirion 2006 all rights reserved, E&OE
• Programmable over-current protection (to
• Thermal shutdown with hysteresis.
• Over-voltage protection
• Under-voltage lockout circuit to disable the
• Soft-start
protect the IC from excessive load current)
converter output when the input voltage is
less than approximately 2.2V
current when the converter is powered up.
OUT
and AGND with the midpoint going
controller
circuit,
limiting
with
a
the
type
in-rush
III
It is recommended that Rb1 and Rb2 resistor
values be ~2kΩ. Use the following equation to
set the resistor Ra1 for the desired output
voltage:
If over-voltage protection is desired, use the
following equation to set the resistor Ra2 for the
desired OVP trip-point:
By design, if both resistor dividers are the same,
the OV trip-point will be 20% above the nominal
output voltage.
Figure 4. V
NOTE: if no OVP divider is present, there will
be no over-voltage protection and POK will
remain “high” as long as V
90% of the nominal V
Input Capacitor Selection
The EN5336QI requires between 10uF and 20uF
of input capacitance. Low-cost, low-ESR ceramic
capacitors should be used as input capacitors for
this converter. The dielectric must be X5R or
X7R rated. In some applications, lower value
capacitors are needed in parallel with the larger,
capacitors in order to provide high frequency
decoupling. It is recommended to use 10V rated
1210 MLCC capacitors.
Ra
Ra
V
7
IN
1
2
=
=
22µF
(
(
C
Vout
OVPtrip
SS
OUT
PVIN
AVIN
−
SS
. 0
and OVP resistor divider networks.
. 0
75
75
. 0
−
V
AGND
90
POK
V
. 0
V
* )
90
V
Rb
PGND
VOUT
* )
XOV
XFB
OUT
1
Rb
setting.
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2
OUT
R
R
a2
b2
remains above
R
R
a1
b1
EN5336QI
47µF
V
OUT