NCP5173MNR2 ON Semiconductor, NCP5173MNR2 Datasheet - Page 12

• Manufacturer Part Number: NCP5173MNR2
• Description: IC PWM BUCK BST FLYBCK INV 8DIP
• Manufacturer: ON Semiconductor
• Type: Step-Up (Boost), Inverting, Flyback, Forward Converter, Sepic, PWM - Current Moder

Specifications of NCP5173MNR2

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adjustable
• Current - Output: 1.5A
• Frequency - Switching: 560kHz
• Voltage - Input: 2.7 ~ 30 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: *
• Package / Case: 8-TDFN Exposed Pad
• Voltage - Supply: 2.7 V ~ 30 V
• Frequency-max: 1MHz
• Duty Cycle: 90%
• Pwm Type: Current Mode
• Buck: Yes
• Boost: Yes
• Flyback: Yes
• Inverting: Yes
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: NCP5173MNR2OS

current is discontinuous and a significant pulsed current is
seen by the input capacitors. Therefore, there are two
requirements for capacitors in a flyback regulator: energy
storage and filtering. To maintain a stable voltage supply to
the chip, a storage capacitor larger than 20 mF with low ESR
is required. To reduce the noise generated by the inductor,
insert a 1.0 mF ceramic capacitor between V
as close as possible to the chip.
Output Capacitor Selection
The situation is different in a flyback circuit. The input
Figure 27. Boost Input Voltage and Current
Figure 29. Typical Output Voltage Ripple
V
Figure 28. Boost Circuit Effective Input Filter
CC
−
+
Ripple Waveforms
I
IN
R
ESR
C
IN
CC
I
and ground
L
V
I
I
I
V
L
IN
L
CC
OUT
http://onsemi.com
ripple
ripple
12
see that the output voltage ripple comes from two major
sources, namely capacitor ESR and the charging/
discharging of the output capacitor. In boost circuits, when
the power switch turns off, I
causing an instant DV = I
I
voltage gradually. When the power switch is turned on, I
shunted to ground and I
When the I
constant and is equal to input current I
output voltage peak−peak ripple can be calculated by:
terms of V
follows:
circuits, similar equations can be derived for flyback
circuits.
Reducing the Current Limit
limit on the switch current than 1.5 A. An external shunt can
be connected between the V
clamp voltage. Consequently, the current limit of the
internal power transistor current is reduced from its nominal
value.
equation:
where:
only available method for limiting switch current below
1.5 A is to clamp the V
maximum switch or inductor current is substituted into the
equation above, the desired clamp voltage will result.
V OUT(RIPPLE) +
V C + I SW R E A V
L
By examining the waveforms shown in Figure 29, we can
The equation can be expressed more conveniently in
The capacitor RMS ripple current is:
Although the above equations apply only for boost
In some applications, the designer may prefer a lower
The voltage on the V
R
A
Since R
V OUT(RIPPLE) +
− I
E
V
I RIPPLE + (I IN * I OUT ) 2 (1 * D))(I OUT ) 2 (D)
= .063 W, the value of the internal emitter resistor;
= 5.0 V/V, the gain of the current sense amplifier.
OUT
E
charges the capacitor and increases the output
L
CC
and A
ripple is small enough, I
+ I OUT
, V
V
OUT
)
I OUT (V OUT * V CC )
cannot be changed by the end user, the
)
(I OUT )(V OUT )(ESR)
(I IN * I OUT) (1 * D)
OUT
(C OUT )(f)
and I
IN
I OUT D
V OUT * V CC
C
(C OUT )(f)
C
× ESR. At the same time, current
(C OUT) (f)
L
pin can be evaluated with the
discharges the output capacitor.
pin at a lower voltage. If the
C
flows into the output capacitor
OUT
V CC
V CC
pin and ground to reduce its
) I IN
for design purposes as
L
IN
can be treated as a
. Summing up, the
ESR
(C OUT )(f)
1
L
is