EP4001_15 Datasheet, PDF (7/10 Pages) Eorex Corporation – High Efficiency, Step-Up Converter with EXT

eorex
EP4001
Low Noise Fixed Frequency Operation Oscillator
The frequency of operation is internally set to 450KHz.
Error Amp: The internal 1.22V reference voltage is compared to the voltage at the FB pin to generate an
error signal at the output of the error amplifier. A voltage divider from V_OUT to ground programs the output
according to the equation:
V_OUT= FB × _⎜⎛1 + ^R1 _⎟⎞
⎝ ^R2 ⎠
Where FB=1.22V
Due to device performance limitation, the EP4001 is limited to applications with output voltage less than
4.2V, until the problem is corrected at later date.
PWM Mode
Refer to Figure 3, functional block diagram. The main gain block is a comparator that sums four signals:
feedback voltage, reference, current-sensing and slope compensation ramp. This direct-summing
method approaches the ideal of cycle-by-cycle control of output voltage. Under heavy loads, the
controller operates in full PWM mode. Every pulse from the oscillator sets the output latch and turns on
the NMOS switch for a period determined by the duty factor and current limit.
PFM Mode Operation
Portable devices frequently spend extended time in low power or standby mode, only switching to high
power mode when specific functions are enabled. Maintain high efficiency over a wide range of load
current is critical for prolong battery life. In addition to its high efficiency at moderate and heavy loads,
the EP4001 includes automatic PFM operation that improves efficiency of the converter at light load.
PFM operation is initiated if the output load current falls below an internally programmed threshold. Once
initiated, the PFM operation circuitry shuts down most of the device, only keeping alive the circuitry
required to monitor the output voltage.
Aug. 2006
www.eorex.com
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