ISL78214_15 Datasheet, PDF (11/15 Pages) Intersil Corporation – 4A Low Quiescent Current High Efficiency Synchronous Buck Regulator

ISL78214
Typical Operating Performance Unless otherwise noted, operating conditions are: T_A = +25°C, V_VIN = 2.5V to 5.5V,
EN = V_IN, SYNCH = 0V, L = 1.5µH, C₁ = 2x22µF, C₂ = 2x22µF, I_OUT = 0A to 4A. (Continued)
LX 2V/DIV
IL 2A/DIV
LX 2V/DIV
V_OUT 0.5V/DIV
PG 5V/DIV
V_OUT 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_3.3V_IN
5.125
5.000
4.875
4.750
OCP_5V_IN
4.625
4.500-50
-25
0
25
50
TEMPERATURE (°C)
75
100
FIGURE 35. OUTPUT CURRENT LIMIT vs TEMPERATURE
Theory of Operation
The ISL78214 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 ISL78214 employs the
current-mode Pulse-width Modulation (PWM) control scheme for
fast transient response and pulse-by-pulse current limiting. Figure 2
on page 3 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 V_EAMP 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 signal
to a current output. The voltage loop is internally compensated
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FN7551.3
May 12, 2015