ISL8014 Ver la hoja de datos (PDF) - Intersil
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ISL8014 Datasheet PDF : 16 Pages
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ISL8014
Typical Operating Performance (Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 2.5V to 5.5V, EN = VIN,
SYNCH = 0V, L = 1.5µH, C1 = 2x22µF, C2 = 2x22µF, IOUT = 0A to 4A). (Continued)
LX 2V/DIV
IL 2A/DIV
LX 2V/DIV
VOUT 0.5V/DIV
PG 5V/DIV
VOUT 1V/DIV
PG 5V/DIV
IL 2A/DIV
FIGURE 33. OUTPUT SHORT CIRCUIT
FIGURE 34. OUTPUT SHORT CIRCUIT RECOVERY
5.500
5.375
5.250
OCP_3.3VIN
5.125
5.000
4.875
4.750
OCP_5VIN
4.625
4.500-50
-25
0
25
50
TEMPERATURE (°C)
75
100
FIGURE 35. OUTPUT CURRENT LIMIT vs TEMPERATURE
Theory of Operation
The ISL8014 is a step-down switching regulator optimized for
battery-powered handheld applications. The regulator operates
at 1MHz fixed switching frequency under heavy load conditions
to allow smaller external inductors and capacitors to be used for
minimal printed-circuit board (PCB) area. At light load, the
regulator reduces the switching frequency, unless forced to the
fixed frequency, to minimize the switching loss and to maximize
the battery life. The quiescent current when the output is not
loaded is typically only 35µA. The supply current is typically
only 0.1µA when the regulator is shut down.
PWM Control Scheme
Pulling the SYNCH pin HI (>2.5V) forces the converter into
PWM mode, regardless of output current. The ISL8014
employs the current-mode pulse-width modulation (PWM)
control scheme for fast transient response and pulse-by-pulse
current limiting. Figure 2 shows the block diagram. The current
loop consists of the oscillator, the PWM comparator, current
sensing circuit and the slope compensation for the current loop
stability. The gain for the current sensing circuit is typically
200mV/A. The control reference for the current loops comes
from the error amplifier's (EAMP) output.
The PWM operation is initialized by the clock from the
oscillator. The P-Channel MOSFET is turned on at the
beginning of a PWM cycle and the current in the MOSFET
starts to ramp up. When the sum of the current amplifier CSA
and the slope compensation (237mV/µs) reaches the control
reference of the current loop, the PWM comparator COMP
sends a signal to the PWM logic to turn off the P-MOSFET
and turn on the N-Channel MOSFET. The N-MOSFET stays
on until the end of the PWM cycle. Figure 36 shows the typical
operating waveforms during the PWM operation. The dotted
lines illustrate the sum of the slope compensation ramp and
the current-sense amplifier’s CSA output.
The output voltage is regulated by controlling the VEAMP
voltage to the current loop. The bandgap circuit outputs a
0.8V reference voltage to the voltage loop. The feedback
signal comes from the VFB pin. The soft-start block only
affects the operation during the start-up and will be
discussed separately. The error amplifier is a
transconductance amplifier that converts the voltage error
12
FN6576.1
December 20, 2007
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