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PDF SC171 Data sheet ( Hoja de datos )
| Número de pieza | SC171 | |
| Descripción | Synchronous Step-Down Regulator | |
| Fabricantes | Semtech | |
| Logotipo |  |
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SC171
POWER MANAGEMENT
1A EcoSpeedTM Synchronous Step-Down
Regulator with Optional Ultrasonic Power Save
Features
VIN: 3V to 5.5V
VOUT: 0.75V to 95% x VIN
IOUT: Up to 1A
Low RDS(ON) Switches
Up to 95% Peak Efficiency
High Output Accuracy
Small Ceramic Capacitors
Power Good Pin (Open-Drain)
Patented Adaptive On-Time Control:
Excellent Transient Response
Programmable Pseudo-fixed Frequency
Fault Protection Features:
Cycle-by-Cycle Current Limit
Short Circuit Protection
Over and Under Output Voltage Protection
Over-Temperature
Internal Soft start
Ultrasonic Power Save
Smart Power Save
Ultra-Small Lead-Free 3x3mm, 10-Pin MLPD Package
Fully WEEE and RoHS Compliant
Applications
Networking Equipment, Embedded Systems
Medical Equipment, Office Automation
Instrumentation, Portable Systems
Consumer Devices (DTV, Set-top Box, ... )
5V POL Converters
Description
The SC171 is an integrated, synchronous 1A EcoSpeedTM
step-down regulator, which incorporates Semtech’s
advanced, patented adaptive on-time architecture to
achieve best-in-class performance in dynamic point-of-
load applications. The input voltage range is 3V to 5.5V
with a programmable output voltage from 0.75V up to
95% x VIN. The device features low-RDS(ON) internal switch-
es and optional PSAVE mode for high efficiency across
the output load range.
Adaptive on-time control provides programmable pseu-
do-fixed frequency operation and excellent transient
performance. The switching frequency can be set from
200kHz to 1MHz - allowing the designer to reduce exter-
nal LC filtering and minimize light load (standby) losses.
Disabling PSAVE operation reduces output voltage ripple
at light load for ceramic output capacitors.
Additional features include cycle-by-cycle current limit,
soft start, input UVLO and output OV protection, and
over temperature protection. The open-drain PGOOD
pin provides output status. Standby current is less than
10μA when disabled.
The device is available in a low profile, thermally en-
hanced MLPD-3x3mm 10-pin package.
Typical Application Circuit
3 to 5.5V
VIN BST
LX
SC 171
VOUT = 0.75 V to 95% VIN
VDD
FB
PGOOD
Power Good
Enable /
Power Save
EN/ PSV
PGND
TON
AGND
October 11 , 2010
© 2010 Semtech Corporation
1 page  
Electrical Characteristics (continued)
Unless specified: VIN =5V, TA=+25°C for Typ, -40°C to +85°C for Min and Max, TJ < 125°C
Parameter
Symbol
Conditions
Enable/Power Save
Output Enabled
Output Disabled
EN/PSV Input Bias Current
EN/PSV = VDD or 0V
Power Save Enabled
Forced Continuous Conduction Mode
EN/PSV floating
Gate Drivers
BST Switch On resistance
Internal Power MOSFETs
Current Limit
Valley Current Limit, VDD=5V
Valley Current Limit, VDD=3V
LX Leakage Current
VIN=5.5V, LX=0V, High Side
Switch Resistance
High Side
Low Side
Non-overlap time (1)
Note:
(1) Typical value from EVB, not ATE tested.
SC171
Min Typ Max Units
1V
0.4 V
0.5 8.0 μA
60 %VDD
39 41 44 %VDD
40 75 Ω
1.5 2.2
1 1.4
A
1 10 µA
105 160
mΩ
85 130
30 ns
© 2010 Semtech Corporation
5 Page 
SC171
Applications Information
SC171 Synchronous Buck Converter
The SC171 is a step down synchronous buck dc-dc regu-
lator. The SC171 is capable of 1A operation at very high
efficiency in a tiny 3x3-10 pin package. The programma-
ble operating frequency range of 200kHz – 1MHz enables
the user to optimize the solution for minimum board
space and optimum efficiency.
The buck regulator employs pseudo-fixed frequency
adaptive on-time control. This control scheme allows
fast transient response thereby lowering the size of the
power components used in the system.
Input Voltage Range
The SC171 can operate with an input voltage ranging
from 3V to 5.5V.
Psuedo-fixed Frequency Adaptive On-time Control
The adaptive on-time is determined by an internal one-
shot timer. When the one-shot is triggered by the out-
put ripple, the device sends a single on-time pulse to the
high-side MOSFET. The pulse period is determined by
VOUT and VIN; the period is proportional to output voltage
and inversely proportional to input voltage. With this
adaptive on-time arrangement, the device automatically
anticipates the on-time needed to regulate VOUT for the
present VIN condition and at the selected frequency.
The advantages of adaptive on-time control are:
• Predictable operating frequency compared to
• other variable frequency methods.
Reduced component count by eliminating
the error amplifier and compensation compo-
• nents.
Reduced component count by removing the
• need to sense and control inductor current.
Fast transient response — the response time
is controlled by a fast comparator instead of a
• typically slow error amplifier.
Reduced output capacitance due to fast tran-
sient response
The PWM control method used by the SC171 is pseudo-
fixed frequency, adaptive on-time, as shown in Figure 1.
The ripple voltage generated at the output capacitor ESR
is used as a PWM ramp signal. This ripple is used to trig-
ger the on-time of the controller.
Q1
Q2
VIN
TON
CIN
VFB
L
VLX
ESR
VLX
FB threshold
VOUT
One-Shot Timer and Operating Frequency
The one-shot timer operates as shown in Figure 2. The
FB Comparator output goes high when VFB is less than
the internal 750mV reference. This feeds into the gate
drive and turns on the high-side MOSFET, and also starts
the one-shot timer. The one-shot timer uses an internal
comparator, timing capacitor, and a low pass filter (LPF)
which regenerates VOUT from LX. One comparator input
is connected to the filtered LX voltage, the other input is
connected to the capacitor. When the on-time begins,
the internal capacitor charges from zero volts through a
current which is proportional to VIN. When the capacitor
voltage reaches VOUT, the on-time is completed and the
high-side MOSFET turns off.
+ This method automatically produces an on-time that is
COUT FB proportional to VOUT and inversely proportional to VIN.
Under steady-state operation conditions, the switching
frequency can be determined from the on-time by the
following equation.
Figure 1 — PWM Control Method, VOUT Ripple
© 2010 Semtech Corporation
fSW
=
VOUT
TON × VIN
11
11 Page | ||
| Páginas | Total 27 Páginas | |
| PDF Descargar | [ Datasheet SC171.PDF ] | |
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