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EN6360QI

8A Synchronous Highly Integrated DC-DC PowerSoC

Enpirion, Inc. 

EN6360QI

Functional Description

The EN6360QI is a synchronous, programmable

buck power supply with integrated power MOSFET

switches and integrated inductor. The switching

supply uses voltage mode control and a low noise

PWM topology. This provides superior impedance

matching to ICs processed in sub 90nm process

technologies. The nominal input voltage range is

2.5 - 6.6 volts. The output voltage is programmed

using an external resistor divider network. The

feedback control loop incorporates a type IV

voltage mode control design. Type IV voltage mode

control maximizes control loop bandwidth and

maintains excellent phase margin to improve

transient performance. The EN6360QI is designed

to support up to 8A continuous output current

operation. The operating switching frequency is

between 0.9MHz and 1.5MHz and enables the use

of small-size input and output capacitors.

The power supply has the following features:

• Precision Enable Threshold

• Soft-Start

• Pre-bias Start-Up

• Resistor Programmable Switching Frequency

• Phase-Lock Frequency Synchronization

• Parallel Operation

• Power OK

• Over-Current/Short Circuit Protection

• Thermal Shutdown with Hysteresis

• Under-Voltage Lockout

Precision Enable

The ENABLE threshold is a precision analog

voltage rather than a digital logic threshold. A

precision voltage reference and a comparator

circuit are kept powered up even when ENABLE is

de-asserted. The narrow voltage gap between

ENABLE Logic Low and ENABLE Logic High

allows the device to turn on at a precise enable

voltage level. With the enable threshold pinpointed,

a proper choice of soft-start capacitor helps to

accurately sequence multiple power supplies in a

system as desired. There is an ENABLE lockout

time of 2ms that prevents the device from re-

enabling immediately after it is disabled.

Soft-Start

The SS pin in conjunction with a small external

capacitor between this pin and AGND provides a

soft-start function to limit in-rush current during

device power-up. When the part is initially powered

up, the output voltage is gradually ramped to its

final value. The gradual output ramp is achieved by

increasing the reference voltage to the error

amplifier. A constant current flowing into the soft-

start capacitor provides the reference voltage ramp.

When the voltage on the soft-start capacitor

reaches 0.60V, the output has reached its

programmed voltage. Once the output voltage has

reached nominal voltage the soft-start capacitor will

continue to charge to 1.5V (Typical). The output

rise time can be controlled by the choice of soft-

start capacitor value.

The rise time is defined as the time from when the

ENABLE signal crosses the threshold and the input

voltage crosses the upper UVLO threshold to the

time when the output voltage reaches 95% of the

programmed value. The rise time (tRISE) is given by

the following equation:

tRISE [ms] = Css [nF] x 0.065

The rise time (tRISE) is in milliseconds and the soft-

start capacitor (CSS) is in nano-Farads. The soft-

start capacitor should be between 10nF and 100nF.

Pre-Bias Start-up

The EN6360QI supports startup into a pre-biased

load. A proprietary circuit ensures the output

voltage rises up from the pre-bias value to the

programmed output voltage. Start-up is guaranteed

to be monotonic for pre-bias voltages in the range

of 20% to 75% of the programmed output voltage

with a minimum pre-bias voltage of 300mV. Outside

of the 20% to 75% range, the output voltage rise

will not be monotonic. The Pre-Bias feature is

automatically engaged with an internal pull-up

resistor. For this feature to work properly, VIN must

be ramped up prior to ENABLE turning on the

device. Tie VSENSE to VOUT if Pre-Bias is used.

Tie EN_PB to ground and leave VSENSE floating

to disable the Pre-Bias feature. Pre-Bias is

supported for external clock synchronization, but

not supported for parallel operations.

Resistor Programmable Frequency

The operation of the EN6360QI can be optimized

by a proper choice of the RFQADJ resistor. The

frequency can be tuned to optimize dynamic

performance and efficiency. Refer to Table 1 for

recommended RFQADJ values.

©Enpirion 2011 all rights reserved, E&OE

06489

Enpirion Confidential

April 16, 2012

www.enpirion.com, Page 14

Rev: C

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