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EN5336QI

3A PowerSoC Voltage Mode Synchronous Buck With Integrated Inductor Output Voltage Programming

Altera Corporation 

EN5336QI

Theory of Operation

Synchronous Buck Converter

The EN5336QI is a synchronous, pin

programmable power supply with integrated

power MOSFET switches and integrated

inductor. The nominal input voltage range is 2.4-

5.0V. The output can be set to any voltage

between 0.75V and VIN – 600mV. The feedback

control loop is a type III voltage-mode and the

part uses a low-noise PWM topology. Up to 3A of

output current can be drawn from this converter.

The 5MHz operating frequency enables the use

of small-size output capacitors.

The power supply has the following protection

features:

 Over-current protection (to protect the IC

from excessive load current)

 Thermal shutdown with hysteresis

 Over-voltage protection

 Under-voltage lockout circuit to disable the

converter output when the input voltage is

less than approximately 2.2V

Additional features include:

set the resistor Ra1 for the desired output

voltage:

Ra1  (Vout  0.75V ) * Rb1

0.75V

If over-voltage protection is desired, use the

following equation to set the resistor Ra2 for the

desired OVP trip-point:

Ra2  (OVPtrip  0.90V ) * Rb2

0.90V

By design, if both resistor dividers are the same,

the OV trip-point will be 20% above the nominal

output voltage.

VIN

22F

CSS

PVIN

AVIN

SS

POK

VOUT

AGND

XOV

XFB

PGND

Ra2 Ra1

Rb2 Rb1

VOUT

47F

Figure 4. VOUT and OVP resistor divider networks.

 Soft-start circuit, limiting the in-rush

current when the converter is powered up

 Power good circuit indicating whether the

output voltage is within 90% - 120% of the

programmed voltage

Output Voltage Programming

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 VOUT and AGND with the midpoint going

to XFB and XOV.

NOTE: if no OVP divider is present, there will be

no over-voltage protection and POK will remain

“high” as long as VOUT remains above 90% of the

nominal VOUT setting.

Input Capacitor Selection

The EN5336QI requires about 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

MLCC capacitors. Table 2 lists some

recommended part numbers for input capacitors.

It is recommended that Rb1 and Rb2 resistor

values be ~2k. Use the following equation to

8

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