Data Sheet ADP1614
CURRENT-MODE PWM OPERATION
The ADP1614 utilizes a current-mode PWM control scheme to
regulate the output voltage over all load conditions. The output
voltage is monitored at FB through a resistive voltage divider. The
voltage at FB is compared with the internal 1.245 V reference by
the internal transconductance error amplifier to create an error
voltage at COMP. The current of the switch is internally measured
and added to the stabilizing ramp. The resulting sum is compared
with the error voltage at COMP to control the PWM modulator.
This current-mode regulation system allows fast transient response
while maintaining a stable output voltage. By selecting the proper
resistor-capacitor network from COMP to GND, the regulator
response is optimized for a wide range of input voltages, output
voltages, and load conditions.
ADJUSTABLE CURRENT LIMIT
A key feature of the ADP1614ACPZ-650-R7 and
ADP1614ACPZ-1.3-R7 is a pin-adjustable peak current limit of
up to 4 A (see Figure 10 to Figure 13 and Figure 33). This adjustable
current limit allows the other external components to be selected
specifically for the application. The current limit is set via an
external resistor connected from Pin 9 (CLRES) to ground. For
the ADP1614ACPZ-R7, the current limit is fixed at 3 A.
60 1501351201059075
CURRENT LIM IT ( A)
RCL (kΩ)
1.0
4.0
3.5
3.0
2.5
2.0
1.5
VIN = 3.5V
10293-007
VOUT = 15V
VOUT = 5V
Figure 33. Peak Current Limit of Switch vs. RCL
FREQUENCY SELECTION
The adjustable current-limit versions of the ADP1614 are
internally programmed to operate at either 650 kHz or 1.3 MHz.
Operation of the ADP1614 at 650 kHz (ADP1614ACPZ-650-R7)
optimizes the efficiency of the device, whereas operation of the
ADP1614 at 1.3 MHz (ADP1614ACPZ-1.3-R7) enables the
device to be used with smaller external components. For the
fixed current-limit version (ADP1614ACP-R7), the frequency is
pin selectable via the FREQ Pin (Pin 9). Connect FREQ to
GND for 650 kHz operation or connect FREQ to VIN for
1.3 MHz operation. Do not leave the FREQ pin floating.
SOFT START
To prevent input inrush current to the converter when the part
is enabled, connect a capacitor from SS to GND to set the soft
start period. After the ADP1614 is turned on, SS sources 5 µA
(typical) to the soft start capacitor (CSS) until it reaches 1.23 V at
startup. As the soft start capacitor charges, it limits the peak current
allowed by the part. By slowly charging the soft start capacitor,
the input current ramps slowly to prevent it from overshooting
excessively at startup. When the ADP1614 is disabled, the SS
pin is internally shorted to GND to discharge the soft start
capacitor.
THERMAL SHUTDOWN (TSD)
The ADP1614 includes TSD protection. If the die temperature
exceeds 150°C (typical), TSD turns off the NMOS power device,
significantly reducing power dissipation in the device and
preventing output voltage regulation. The NMOS power device
remains off until the die temperature is reduced to 130°C (typical).
The soft start capacitor is discharged during TSD to ensure low
output voltage overshoot and inrush currents when regulation
resumes.
UNDERVOLTAGE LOCKOUT (UVLO)
If the input voltage is below the UVLO threshold, the ADP1614
automatically turns off the power switch and places the part
into a low power consumption mode. This prevents potentially
erratic operation at low input voltages and prevents the power
device from turning on when the control circuitry cannot
operate it. The UVLO levels have ~100 mV of hysteresis to
ensure glitch-free startup.
SHUTDOWN MODE
The EN pin turns the ADP1614 regulator on or off. Drive EN
low to shut down the regulator and reduce the input current to
0.25 µA (typical). Drive EN high to turn on the regulator.
When the converter is in shutdown mode (EN ≤ 0.3 V), there is a
dc path from the input to the output through the inductor and
output rectifier. This causes the output voltage to remain slightly
below the input voltage by the forward voltage of the rectifier,
preventing the output voltage from dropping to ground when the
regulator is shut down.
Regardless of the state of the EN pin, when a voltage is applied to
the VIN pin, a large current spike occurs due to the nonisolated
path through the inductor and diode between VIN and VOUT. The
high current is a result of the output capacitor charging. The
peak value is dependent on the inductor, output capacitor, and
any load active on the output of the regulator.
Rev. B | Page 13 of 18