ncp1596 ON Semiconductor, ncp1596 Datasheet - Page 10

• Manufacturer Part Number: ncp1596
• Description: 1.5 A, 1.5 Mhz Current Mode Pwm Buck Down Converter
• Manufacturer: ON Semiconductor

Introduction
switching frequency at 1.5 MHz. High operation frequency
can reduce the capacitor value and PCB area. Also, more
features are built in this converter.
solutions to applications. A simple function block diagram
and timing diagram are shown in Figure 1 and Figure 2.
Soft−Start and Current Limit
in−rush current during startup. This helps to reduce the
output voltage over−shoot.
excess of 2 A. The intended output current of the system is
1.5 A. The ripple current is calculated to be approximately
350 mA with a 3.3 mH inductor. Therefore, the peak current
at 1.5 A output will be approximately 1.7 Amps. A 2.5 Amp
set point will allow for transient currents during load step.
The current limit circuit is implemented as a cycle−by−cycle
current limit. Each on−cycle is treated as a separate situation.
Current limiting is implemented by monitoring the
P−channel switch current buildup during conduction with a
current limit comparator. The output of the current limit
comparator resets the PWM latch, immediately terminating
the current cycle. When output loading is short circuit,
device will auto restart with soft start.
Error Amplifier and Slope Compensation
inside NCP1596. No external circuitry is needed to stabilize
the device. The error amplifier provides an error signal to the
PWM comparator by comparing the feedback voltage
(800 mV) with internal voltage reference of 1.2 V.
cycles over 50%. A slope compensation circuit is provided
The NCP1596 is a current−mode buck converter with
The upper feature can provide more cost effective
A soft start circuit is internally implemented to reduce the
The current limit is set to allow peak switch current in
A fully internal compensated error amplifier is provided
Current mode converter can exhibit instability at duty
1. Internal 1 ms soft−start to avoid inrush current at
2. Internal cycle by cycle current limit provides an
3. Internal compensation. No external compensation
4. Thermal shutdown protects the devices from over
5. 100% duty cycle allowed. Speed up transient load
startup.
output short circuit protection.
components are necessary.
heat.
response.
DETAILED OPERATING DESCRIPTION
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inside NCP1596 to overcome the potential instability. Slope
compensation consists of a ramp signal generated by the
synchronization block and adding this to the inductor
current signal. The summed signal is then applied to the
PWM comparator.
Thermal Shutdown
protect the integrated circuit in the event when maximum
junction temperature is exceeded. When activated, typically
at 180°C, the shutdown signal will disable the P−channel
switch. The thermal shutdown circuit is designed with 30°C
of hysteresis. This means that the switching will not start
until the die temperature drops by this amount. This feature
is provided to prevent catastrophic failures from accidental
device overheating. It is not intended as a substitute for
proper heat sinking. NCP1596 is contained in the
thermally enhanced QFN package.
Under Voltage Lockout (UVLO)
when input voltage is very low. In NCP1596, the UVLO
level is set to 3.5 V. If the input voltage is less than 3.5 V, the
converter will shutdown itself automatically.
Low Power Shutdown Mode (EN)
to ground. During the shutdown mode, the internal
reference, oscillator and driver control circuits will be turn
off, the device only consume 1 mA typically and output
voltage will be discharge to zero by the external resistor
divider. EN pin has an internal pull−up current source, which
typical value is 500 nA.
Power Saving Pulse−Frequency−Modulation (PFM)
Control Scheme
enters
operation. In DCM operation, the on−time (T
integrated switch for each switching cycle will decrease
when the output current decreases. In order to maintain a
high converter efficiency at light load condition. A
minimum T
fixed power send to output. To avoid a higher switch loss
occurs when without loading apply. This control scheme can
reduce the switching loss at light load and improve the
conversion efficiency.
Internal Thermal Shutdown circuitry is provided to
UVLO function is used to ensure the logic level correctly
NCP1596A can be disabled whenever the EN pin is tied
While the converter loading decreases, the converter
the
on
is set to 70 ns. It can make sure a minimum
Discontinues−conduction−mode
on
) of the
(DCM)