ncv890201 ON Semiconductor, ncv890201 Datasheet - Page 11

• Manufacturer Part Number: ncv890201
• Description: Automotive Buck Switching Regulator
• Manufacturer: ON Semiconductor

INPUT VOLTAGE
input, and inhibits switching and resets the Soft−start circuit
if there is insufficient voltage for proper regulation. The
NCV890201 can regulate a 3.3 V output with input voltages
above 4.5 V and a 5.0 V output with an input above 6.5 V.
the Power Switch, the switching frequency is reduced by a
factor of 2 when the input voltage exceeds the V
Frequency Foldback threshold V
Frequency reduction is automatically terminated when the
input voltage drops back below the V
threshold V
ENABLE
signal or battery voltage as an Enable signal. EN low induces
a ’sleep mode’ which shuts off the regulator and minimizes
its supply current to a couple of mA typically (I
disabling all functions. Upon enabling, voltage is
established at the DRV pin, followed by a soft−start of the
switching regulator output.
SOFT−START
and after the DRV voltage is established, a soft−start circuit
ramps the switching regulator error amplifier reference
voltage to the final value. During soft−start, the average
switching frequency is lower than its normal mode value
(typically 2 MHz) until the output voltage approaches
regulation.
ERROR AMPLIFIER
The output voltage of the error amplifier controls the peak
(MHz)
Fsw
An Undervoltage Lockout (UVLO) circuit monitors the
The NCV890201 withstands input voltages up to 40 V.
To limit the power lost in generating the drive voltage for
The NCV890201 is designed to accept either a logic level
Upon being enabled or released from a fault condition,
The error amplifier is a transconductance type amplifier.
2
1
Figure 27. NCV890201 Switching Frequency
4
Reduction at High Input Voltage
FLDDN
.
18 20
FLDUP
IN
Frequency Foldback
(see Figure 27).
GENERAL INFORMATION
36
qSD
http://onsemi.com
VIN (V)
) by
IN
11
inductor current at which the power switch shuts off. The
Current Mode control method employed by the NCV890201
allows the use of a simple, Type II compensation to optimize
the dynamic response according to system requirements.
SLOPE COMPENSATION
and added to the sensed current to avoid increased output
voltage ripple due to bifurcation of inductor ripple current
at duty cycles above 50%. The fixed amplitude of the slope
compensation signal requires the inductor to be greater than
a minimum value, depending on output voltage, in order to
avoid sub−harmonic oscillations. For 3.3 V and 5 V output
voltages, the recommended inductor value is 4.7 mH.
SHORT CIRCUIT FREQUENCY FOLDBACK
NCV890201 automatically reduces its switching frequency.
This creates duty cycles small enough to limit the peak
current in the power components, while maintaining the
ability to automatically reestablish the output voltage if the
overload is removed. If the current is still too high after the
switching frequency folds back to 500 kHz, the regulator
enters an auto−recovery burst mode that further reduces the
dissipated power.
CURRENT LIMITING
output current of a buck converter is lower than the peak
current setpoint of the regulator. Figure 28 shows − for a
4.7 mH inductor − how the variation of inductor peak current
with input voltage affects the maximum DC current the
NCV890201 can deliver to a load.
A fixed slope compensation signal is generated internally
During severe output overloads or short circuits, the
Due to the ripple on the inductor current, the average
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
0
Figure 28. NCV890201 Load Current Capability
5
10
(5 V
with 4.7 mH Inductor
INPUT VOLTAGE (V)
OUT
15
)
20
(3.3 V
25
OUT
30
)
35
40