ER3105DI Datasheet, PDF(18/25 Page) Altera Corporation – 500mA Wide VIN Synchronous Buck Regulator

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ER3105DI Datasheet, PDF (18/25 Pages) Altera Corporation – 500mA Wide VIN Synchronous Buck Regulator

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Page 18

PWM

DCM

PULSE SKIP

DCM

PWM

OCK

8 CYCLES

LOAD CURRENT

VOUT

FIGURE 57. DCM MODE OPERATION WAVEFORMS

Due to the pulsed current nature of PFM mode, the converter can supply limited current to the load. Should load current rise

beyond the limit, VOUT will begin to decline. A second comparator signals an FB voltage 1% lower than the 600mV reference

and forces the converter to return to PWM operation.

Output Voltage Selection

The regulator output voltage is easily programmed using an external resistor divider to scale VOUT relative to the internal reference

voltage. The scaled voltage is applied to the inverting input of the error amplifier; refer to Figure 57.

The output voltage programming resistor, R3, depends on the value chosen for the feedback resistor, R2, and the desired output

voltage, VOUT, of the regulator. Equation 3 describes the relationship between VOUT and resistor values.

R3 = V-----O-R---U-2---T-x---0-â---.-6-0---.V--6---V---

(EQ. 3)

If the desired output voltage is 0.6V, then R3 is left unpopulated and R2 is 0â¦.

VOUT

0.6V

REFERENCE

FIGURE 58. EXTERNAL RESISTOR DIVIDER

Protection Features

The ER3105DI is protected from overcurrent, negative overcurrent and over-temperature. The protection circuits operate

automatically.

Overcurrent Protection

During PWM on-time, current through the upper FET is monitored and compared to a nominal 0.9A peak overcurrent limit. In the

event that current reaches the limit, the upper FET will be turned off until the next switching cycle. In this way, FET peak current

is always well limited.

If the overcurrent condition persists for 17 sequential clock cycles, the regulator will begin its hiccup sequence. In this case, both

FETS will be turned off and POK will be pulled low. This condition will be maintained for 8 soft-start periods after which, the

regulator will attempt a normal soft-start.

ER3105DI 500mA Wide VIN Synchronous Buck Regulator

09616

March 14, 2014

March 2014 Altera Corporation

Rev A

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