ncv8881 ON Semiconductor, ncv8881 Datasheet - Page 29

• Manufacturer Part Number: ncv8881
• Description: Ncv8881 1.5a Automotive Buck Regulator With Watchdog
• Manufacturer: ON Semiconductor

ENABLE
Input Capacitors
4.7 mF placed between the VIN pin and the ground terminal
of the SMPS freewheeling diode in order to reduce input
voltage perturbations present when the NCV8881 SMPS is
heavily loaded. A secondary 0.1 mF ceramic capacitor
positioned as closely as possible between the VIN and GND
pins of the NCV8881 provides greater reduction of input
perturbations than further increasing the value of the
primary ceramic capacitor, and can be more effectively
positioned than the larger 4.7 mF capacitor without
compromising PCB thermal conductivity.
LDO Output Capacitor Selection
capacitors above 3.3 mF having an ESR from 200 mW up to
5 W over the full range of output current and temperature.
Lower capacitance and ESR can be used for lighter load
3.3V
RESB
The primary input capacitor should be a ceramic of at least
The LDOs have been compensated to work with output
RESB
3.3V
WDI
5V
VIN
Figure 57. RESB Pulled Low as the SMPS Output Voltage (pullup source for RESB) Drops Out of Regulation
0
SMPS OUTPUT OUT OF REGULATION TO RESB LOW DELAY
WATCHDOG STUCK HIGH; ENABLE = LOW, THEN EN = HIGH RESTARTS
0
Figure 56. Watchdog Stuck HIGH, EN Input LOW; then EN Goes HIGH to Restart the Regulators
DELAY
1
POR
1
2
2
BOOT DELAY
3
3
NORMAL RESPONSE
4
4
5
WATCHDOG
APPLICATION INFORMATION
5
DELAY
6
WDI STUCK HIGH
http://onsemi.com
6
7
29
8
7
requirements.
Electrolytic, capacitors can be used. Ceramic capacitors
should have series resistance added to be within the
recommended ESR range. There are many capacitor
vendors which supply automotive rated parts that fall within
these ranges. For example, the SUNCON EP−series
Aluminum Electrolytic capacitors are well suited well for
automotive radio applications.
Setting the SMPS Output Voltage
the following equation:
connected from V
connected from the FB pin to ground. To reduce the effect
To set the output voltage of the switching regulator, use
where V
9
tFBLDLY
8
THRESHOLD
VFBMONL
10
REF
9
V
is the Reference voltage, R1 is the resistor
SWOUT
11
Tantalum,
SWOUT
10
DELAY
POR
+ V
12
to the FB pin and R2 is the resistor
REF
11
13
BOOT DELAY
Aluminum
1 )
12
14
R1
R2
NORMAL RESPONSE
15
13
or
Polymer
16
(eq. 1)
14