NCV5171EDR2G ON Semiconductor, NCV5171EDR2G Datasheet - Page 10

• Manufacturer Part Number: NCV5171EDR2G
• Description: IC REG BOOST 1.5A 280KHZ 8-SOIC
• Manufacturer: ON Semiconductor
• Type: Step-Up (Boost), Inverting, Flyback, Forward Converter, Sepicr

Specifications of NCV5171EDR2G

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Current - Output: 1.5A
• Frequency - Switching: 280kHz
• Voltage - Input: 2.7 ~ 30 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Mounting Style: SMD/SMT
• Operating Temperature Range: - 40 C to + 150 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Switch Driver and Power Switch
section to drive the output power switch. The switch is
grounded through emitter resistors (63 mW total) to the
PGND pin. PGND is not connected to the IC substrate so that
switching noise can be isolated from the analog ground. The
peak switching current is clamped by an internal circuit. The
clamp current is guaranteed to be greater than 1.5 A and
varies with duty cycle due to slope compensation. The
power switch can withstand a maximum voltage of 40 V on
the collector (V
is typically less than 1 V to minimize power dissipation.
Short Circuit Condition
the inductor current will increase during the whole
switching cycle, causing excessive current to be drawn from
the input power supply. Since control ICs don’t have the
means to limit load current, an external current limit circuit
(such as a fuse or relay) has to be implemented to protect the
load, power supply and ICs.
prevents damage to the chip and external components. This
feature reduces the minimum duty cycle and allows the
transformer secondary to absorb excess energy before the
switch turns back on.
the V
Startup waveforms shown in Figure 25 are measured in the
boost converter demonstrated in the Application Diagram
on the page 2 of this document. Recorded after the input
voltage is turned on, this waveform shows the various
phases during the power up transition.
voltage, the V
current conducts directly from the input power source to the
output through the inductor and diode. Once V
The switch driver receives a control signal from the logic
When a short circuit condition happens in a boost circuit,
In other topologies, the frequency shift built into the IC
The NCV5171/73 can be activated by either connecting
When the V
Figure 25. Startup Waveforms of Circuit Shown in
CC
the Application Diagram. Load = 400 mA.
pin to a voltage source or by enabling the SS pin.
CC
SW
SW
pin). The saturation voltage of the switch
voltage is below the minimum supply
pin is in high impedance. Therefore,
CC
reaches
http://onsemi.com
V
V
I
V
L
OUT
CC
C
10
approximately 1.5 V, the internal power switch briefly turns
on. This is a part of the NCV5171/73’s normal operation.
The turn−on of the power switch accounts for the initial
current swing.
internal power switch starts to switch and a voltage pulse can
be seen at the V
FB pin, the built−in frequency shift feature reduces the
switching frequency to a fraction of its nominal value,
reducing the minimum duty cycle, which is otherwise
limited by the minimum on−time of the switch. The peak
current during this phase is clamped by the internal current
limit.
increases to its nominal value, and the peak current begins
to decrease as the output approaches the regulation voltage.
The overshoot of the output voltage is prevented by the
active pull−on, by which the sink current of the error
amplifier is increased once an overvoltage condition is
detected. The overvoltage condition is defined as when the
FB pin voltage is 50 mV greater than the reference voltage.
COMPONENT SELECTION
Frequency Compensation
desirable transient response and DC regulation while
ensuring the stability of the system. A typical compensation
network, as shown in Figure 26, provides a frequency
response of two poles and one zero. This frequency response
is further illustrated in the Bode plot shown in Figure 27.
DC accuracy over line and load variations. The DC gain of
a transconductance error amplifier can be calculated as
follows:
where:
amplifier output resistance and C1 as:
Gain DC + G M
f P1 +
When the V
When the FB pin voltage rises above 0.4 V, the frequency
The goal of frequency compensation is to achieve
The high DC gain in Figure 27 is desirable for achieving
G
R
The low frequency pole, f
O
M
Figure 26. A Typical Compensation Network
= error amplifier output resistance ≈ 1 MW.
= error amplifier transconductance;
2pC1R O
NCV5171/73
1
C
SW
pin voltage rises above the threshold, the
R O
pin. Detecting a low output voltage at the
GND
V
C
P1,
is determined by the error
R1
C1
C2