SC174MLTRT Semtech, SC174MLTRT Datasheet - Page 12

• Manufacturer Part Number: SC174MLTRT
• Description: IC BUCK SYNC ADJ 4A MLPD-10
• Manufacturer: Semtech
• Series: EcoSpeed™r
• Type: Step-Down (Buck)r

Specifications of SC174MLTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.75 ~ 5.23 V
• Current - Output: 4A
• Frequency - Switching: 200kHz ~ 1MHz
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MLPD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC174MLTR

Applications Information (continued)
V
V
The SC174 uses an external resistor to set the on-time
which indirectly sets the frequency. The on-time can
be programmed to provide operating frequency from
200kHz to 1MHz using a resistor between the TON pin
and ground. The resistor value is selected by the fol-
lowing equation.
V
The switcher output voltage is regulated by comparing
V
the internal 750mV reference voltage, see Figure 3.
output ripple voltage, not the DC value. The DC output
voltage V
the following equation.
REF
© 2010 Semtech Corporation
Note that this control method regulates the valley of the
OUT
IN
FB
OUT
OUT
R
TON
as seen through a resistor divider at the FB pin to
Voltage Selection
On-Shot Timing
-
+
Generator
PWM
V
OUT
Figure 3 — Output Voltage Selection
OUT
V
Time = K x V
Figure 2 — On-Time Generation
OUT
is offset by the output ripple according to
=
0.75V
R
OUT
S
R
TON
/V
IN
Q
⋅
R
=

 

1
1
25pF
+
Lo-Side
Hi-Side
Drivers
Gate
R
and
R
R
1
1
2
2
⋅

 

f
SW
+
V
RIPPLE
2
Q1
Q2
V
V
LX
IN
To FB pin
C
ESR
L
OUT
LPF
+
V
OUT
FB
Enable and Power-save Inputs
The EN/PSV input is used to enable or disable the switch-
ing regulator. When EN/PSV is low (grounded), the switch-
ing regulator is off and in its lowest power state. When
off, the output power switches are tri-stated. When EN/
PSV is allowed to float, the pin voltage will float to 41%
of the voltage at V
with power-save disabled and all switching is in forced
continuous mode.
When EN/PSV is high (above 60% of the voltage at V
the switching regulator turns on with ultrasonic power-
save enabled. The SC174 ultrasonic power-save opera-
tion maintains a minimum switching frequency of 25kHz,
for applications with stringent audio requirements.
Forced Continuous Mode Operation
The SC174 operates in Forced Continuous Mode (FCM)
by floating the EN/PSV pin (see Figure 4). In this mode
one of the power MOSFETs is always on, with no inten-
tional dead time other than to avoid cross-conduction.
This feature results in uniform frequency across the full
load range with the trade-off being poor efficiency at
light loads due to the high-frequency switching of the
MOSFETs.
Voltage (V
DH
DL
Inductor
Current
FB Ripple
Figure 4 — Forced Continuous Mode Operation
DL remains high until V
FB
)
DL drives high when on-time is completed.
DD
On-time
. The switching regulator turns on
(T
ON
)
V
DH on-time is triggered when
FB
FB
reaches the FB Threshold.
falls to the FB threshold.
DC Load Current
FB threshold
DD
(750mV)
12
),