EUP3020
Operation
The EUP3020 has dual independent constant frequency
current mode PWM step-down converters. The
EUP3020 is optimized for low voltage, Li-Ion battery
powered applications where high efficiency and small
size are critical. The EUP3020 uses resistor dividers to
set two output voltages independently from 0.6V to 5V.
The device integrates both main switches and
synchronous rectifiers, which provides high efficiency
and eliminates the need for an external Schottky diode.
The EUP3020 can achieve 100% duty cycle. The duty
cycle D of each step-down converter is defined as:
VOUT
D
=
TON
×
f OSC
×
100%
=
×
100%
VIN
Short Circuit Protection
The EUP3020 has short circuit protection. When any
output is shorted to ground, the own oscillator frequency
is reduced to prevent the inductor current from
increasing beyond the PFET current limit. The PFET
current limit is also reduced to lower the short circuit
current. The frequency and current limit will return to
the normal values once the short circuit condition is
removed and the feedback voltage reaches 0.6V.
Maximum Load Current
The EUP3020 can operate down to 2.5V input voltage,
however the maximum load current decreases at lower
input due to large IR drop on the main switch and
synchronous rectifier. The slope compensation signal
reduces the peak inductor current as a function of the
duty cycle to prevent sub-harmonic oscillations at duty
cycles greater than 50%. Conversely the current limit
increases as the duty cycle decreases.
Where T
ON
is the main switch on time, f
OSC
is the
oscillator frequency (1.5MHz), V
OUT
is the output
voltage and V
IN
is the input voltage.
Current Mode PWM Control
Slope compensated current mode PWM control provides
stable switching and cycle-by-cycle current limit for
superior load and line response and protection of the
internal main switch and synchronous rectifier. Each
channel switches at a constant frequency (1.5MHz) and
regulates the output voltage. During each cycle the
PWM comparator modulates the power transferred to the
load by changing the inductor peak current based on the
feedback error voltage. During normal operation, the
main switch is turned on for a certain time to ramp the
inductor current at each rising edge of the internal
oscillator, and switched off when the peak inductor
current is reached. When the main switch is off, the
synchronous rectifier will be turned on immediately and
stay on until the next cycle starts or the inductor current
starts to reverse.
Dropout Operation
Each channel of the EUP3020 allows the main switch to
remain on for more than one switching cycle and
increases the duty cycle while the input voltage is
dropping close to the output voltage. When the duty
cycle reaches 100%, the main switch is held on
continuously to deliver current to the output up to the
PFET current limit. The output voltage then is the input
voltage minus the voltage drop across the main switch
and the inductor.
DS3020
Ver1.2
Feb. 2009
8
EUTECH [ EUTECH MICROELECTRONICS INC ]
