CS5171EDR8G ON Semiconductor, CS5171EDR8G Datasheet - Page 16

• Manufacturer Part Number: CS5171EDR8G
• Description: IC MULTI CONFIG SYNC 1.5A 8SOIC
• Manufacturer: ON Semiconductor
• Type: Step-Up (Boost), Flyback, Forward Converter, Sepicr

Specifications of CS5171EDR8G

• 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 ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Mounting Style: SMD/SMT
• Rohs Compliant: YES
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: CS5171EDR8GOSTR

V
number of components and allows the Soft−Start circuitry to
activate any time the SS pin is used to restart the converter.
compensation network. At turn on, the voltage at the V
starts to come up, charging capacitor C3 through Schottky
diode D2, clamping the voltage at the V
switching begins when V
typically 1.05 V (refer to graphs for detail over temperature).
the voltage on the V
the size of C3.
function is not used with this part, the cathode of D1 should
be connected to V
Calculating Junction Temperature
designer must calculate the on−chip power dissipation and
determine its expected junction temperature. Internal
thermal protection circuitry will turn the part off once the
junction temperature exceeds 180°C ± 30°. However,
repeated operation at such high temperatures will ensure a
reduced operating life.
but simple task. First, the power losses must be quantified.
There are three major sources of power loss on the CS517x:
•
•
•
linear regulator, requires a small amount of power even
V C + V F(D2) )V C3
SS
IN
This circuit, shown in Figure 40, requires a minimum
Resistor R1 and capacitors C1 and C2 form the
Therefore, C3 slows the startup of the circuit by limiting
Diode D1 discharges C3 when SS is low. If the shutdown
To ensure safe operation of the CS5171/2/3/4, the
Calculation of the junction temperature is an imprecise
The internal control circuitry, including the oscillator and
biasing of internal control circuitry, P
switch driver, P
switch saturation, P
D1
IN
DRIVER
C
.
Figure 40. Soft Start
pin. The Soft−Start time increases with
SAT
SS
C3
D2
C
V
V
reaches the V
CC
C
C1
BIAS
C
R1
C2
pin such that
C
threshold,
http://onsemi.com
C
pin
16
when the switch is turned off. The specifications section of
this datasheet reveals that the typical operating current, I
due to this circuitry is 5.5 mA. Additional guidance can be
found in the graph of operating current vs. temperature. This
graph shows that IQ is strongly dependent on input voltage,
V
drive current must be factored in as well. This current is
drawn from the V
current. The base drive current is listed in the specifications
as DI
designer will find additional guidance in the graphs. With
that information, the designer can calculate
where:
boost converter,
source of on−chip power loss. V
collector−emitter voltage of the internal NPN transistor
when it is driven into saturation by its base drive current. The
value for V
or from the graphs, as “Switch Saturation Voltage.” Thus,
Finally, the total on−chip power losses are
generation of heat in the junctions at the surface of the chip.
This heat is transferred to the surface of the IC package, but
a thermal gradient exists due to the resistive properties of the
package molding compound. The magnitude of the thermal
gradient is expressed in manufacturers’ data sheets as q
or junction−to−ambient thermal resistance. The on−chip
junction temperature can be calculated if q
temperature near the surface of the IC, and the on−chip
power dissipation are known.
D ^
P BIAS + V IN I Q
P DRIVER + V IN I SW
I SW(AVG) ^ I L ( AVG )
I SW(AVG) ^
P SAT ^ V (CE)SAT I SW
P D + P BIAS )P DRIVER )P SAT
IN
Since the onboard switch is an NPN transistor, the base
I
D = the duty cycle or percentage of switch on−time.
I
In a flyback converter,
The switch saturation voltage, V
Power dissipation in a semiconductor device results in the
SW
SW
, and temperature. Then
CC
V OUT )
= the current through the switch;
and D are dependent on the type of converter. In a
/DI
V OUT
SW
(CE)SAT
, or switch transconductance. As before, the
V OUT I LOAD
N S
N P
V IN
IN
V IN
D ^
can be obtained from the specifications
pin, in addition to the control circuitry
V OUT * V IN
DI SW
D
I CC
V OUT
D
Efficiency
Efficiency
D
(CE)SAT
1
1
(CE)SAT
, is the last major
D
1
JA
, the air
is the
JA
Q
,
,