NCP1212P ON Semiconductor, NCP1212P Datasheet - Page 16

• Manufacturer Part Number: NCP1212P
• Description: IC CTRLR PWM PROG CM OVP 8DIP
• Manufacturer: ON Semiconductor
• Type: PWM Controller for Both Forward and Flyback Convertersr

Specifications of NCP1212P

• Output Isolation: Isolated
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 8-DIP (0.300", 7.62mm)
• Input Voltage Range: - 0.3 V to + 28 V
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: Through Hole
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: NCP1212POS

isolated fix switching frequency forward mode converters
that only need few external components to complete the
system. Converting your existing application from using
UC384X controllers to NCP1212 is easy and simple. In
below is a description on how to determine external
components value for a typical application example. For the
schematic of the application, please refer to Figure 1 in this
data sheet.
down into several steps as introduced below:
voltage hitting the Maximum Current Sense Threshold,
V
load change, C
source of 20 mA, I
only be issued until the voltage at SS/DMAX pin falls below
0.5 V. The discharging time, T
capacitor is given by:
CS
The NCP1212 is an ideal choice for next generation
Finding the external component values can be broken
Overload condition is signified by current sense input
. To avoid false trigger that may happen during transient
1. Select the maximum Duty Cycle for forward mode
operation and calculate the Soft- -Start time.
Select the system, operate in forward mode with
82% maximum Duty Cycle. Only a capacitor is
required at SS/DMAX pin and the Soft- -Start time is
determined by the capacitor, C
by the equation below:
where:
I is an 8.0 mA constant current source flow out of the
SS/DMAX pin;
T
SS
T DIS =
is the required Soft- -Start time;
SS
starts to discharge by an internal current
SD
C SS × (V ref − V D − V OL )
C SS =
- -I
SS
and the overload protection will
APPLICATION INFORMATION AND TYPICAL WAVEFORMS
I SD − I SS
V 1 − V 2
I × T SS
DIS
for 0.22 mF Soft- -Start
Figure 40. SS/DMAX Pin Charging Waveform
SS
. Its value is given
http://onsemi.com
115.2 ms
16
where:
C
V
V
reference voltage and SS/DMAX pin in IC internal, is 0.6 V
typical;
V
Overload Detection Block Diagram, the overload threshold
voltage is 0.5 V typical;
SS
ref
D
OL
is the internal diode forward voltage on between the
is the Soft- -Start timing capacitor;
is the internal reference voltage, 5.0 V typical;
is the overload threshold voltage. Refer to Figure 39
V
block and which is effectively controlling the PWM
maximum Duty Cycle at gate driver output.
Soft- -Start block will have no effect to the PWM
operation once SS/DMAX pin voltage reaches this
threshold. This threshold voltage is 2.5 V with 48%
maximum Duty Cycle;
V
which is the Lower Voltage Threshold for the PWM
operation. There will be no PWM gate driver output
before SS/DMAX pin voltage attains this threshold.
For example, the required Soft- -Start time is 50 ms,
the timing capacitor, C
In this case, a 0.22 mF capacitor is used for this
application and the Soft- -Start time is calculated as
57.75 ms. The charging waveform at SS/DMAX pin
is shown in Figure 40. From the captured waveform,
the charge time from 0 V to 4.0 V is 115.2 ms and for
the voltage charging up to 2.5 V, i.e. hitting the
Upper Threshold Voltage, the elapsed time is about
70 ms that matched with the theoretical calculation
closely.
1
2
is the Upper Threshold Voltage in the oscillator
is about 0.4 V (1.0 V minus one diode drop)
C SS =
4.0 V
8 mA × 50 ms
2.5 V − 0.4 V
SS
can be calculated as:
= 0.182 mF