SC4519HSETRT Semtech, SC4519HSETRT Datasheet - Page 7

• Manufacturer Part Number: SC4519HSETRT
• Description: IC STEP DOWN SW REG 3A 8-SOIC
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC4519HSETRT

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Current - Output: 3A
• Frequency - Switching: 600kHz
• Voltage - Input: 4.4 ~ 24 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width) Exposed Pad, 8-eSOIC. 8-HSOIC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Power - Output: -
• Other names: SC4519HSETR

The SC4519H is a current mode buck converter regulator.
SC4519H has an internal fixed-frequency clock. The
SC4519H uses two feedback loops that control the duty
cycle of the internal power switch. The error amplifier
functions like that of the voltage mode converter. The
output of the error amplifier works as a switch current
reference. This technique effectively removes one of the
double poles in the voltage mode system. With this, it is
much simpler to compensate a current mode converter
to have better performance. The current sense amplifier
in the SC4519H monitors the switch current during each
cycle. Overcurrent protection (OCP) is triggered when the
current limit exceeds the upper limit of 3A, detected by a
voltage on COMP greater than about 2V. When an OCP
fault is detected, the switch is turned off and the external
COMP capacitor is discharged at the rate of dv/dt = 3
C
the part enters a normal startup cycle. C
capacitance value attached to COMP. In the case of
sustained overcurrent or dead-short, the part will
continually cycle through the retry sequence as described
above, at a rate dependent on the value of Ccomp. During
start up, the voltage on COMP rises roughly at the rate of
dv/dt = 120
sustained overcurrent can be approximately calculated
as:
Figure 1 shows the voltage on COMP during a sustained
overcurrent condition.
Enable
Pulling and holding the EN pin below 0.4V activates the
shut down mode of the SC4519H which reduces the input
supply current to less than 150
mode, the switch is turned off. The SC4519H is turned
on if the EN pin is pulled high.
POWER MANAGEMENT
Application Information
comp
2007 Semtech Corp.
. Once the COMP voltage has fallen below 250mV,
Figure 1. Voltage on COMP for Startup and OCP
µ
A/C
T
comp
retry
. Therefore, the retry time for a
C
comp
120uA
µ
A. During the shut down
2V
C
comp
comp
is the total
3
2
uA
V
µ
A/
7
Oscillator
Its internal free running oscillator sets the PWM frequency
at 600kHz for the SC4519H without any external
components to program the frequency. An external clock
with a duty cycle from 20% to 80% connected to the
SYNC pin activates synchronous mode. The frequency
of the external clock can be from 700kHz to 1.2MHz.
UVLO
When the EN pin is pulled and held above 1.8V, the voltage
on Pin IN determines the operation of the SC4519H. As
V
V
4.4V.
Load Current
The peak current I
For a specific application, the allowed load current I
will change if the input voltage drifts away from the original
design as given for continuous current mode:
Where:
fs = switching frequency,
Vo = output voltage and
D = duty ratio, V
V
Figure 2 shows the theoretical maximum load current
for the specific cases. In a real application, however, the
allowed maximum load current also depends on the layout
and the air cooling condition. Therefore, the maximum
load current may need to be derated according to the
thermal situation of the application.
IN
IN
I
= input voltage.
increases during power up, the internal circuit senses
and keeps the power transistor off until V
I
O
OMAX
/V
PEAK
I
in the switch is internally limited.
3
V
O
2
1 (
L
f
s
D
)
SC4519H
www.semtech.com
IN
reaches
OMAX