SC4626 Datasheet

SC4626
2.5MHz, 1A Synchronous Step
Down Regulator in SOT23-5
POWER MANAGEMENT
Features
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Description
VIN Range: 2.9 – 5.5V
VOUT Options: 1.0 - 3.3V
Up to 1A Output Current
2.5MHz Switching Frequency
Efficiency Up to 93%
Low Output Noise Across Load Range
Excellent Transient Response
Start Up into Pre-Bias Output
100% Duty-Cycle Low Dropout Operation
<1µA Shutdown Current
Internal Soft Start
Input Under-Voltage Lockout
Output Over-Voltage, Current Limit Protection
Over-Temperature Protection
Adjustable Output Voltage
SOT23-5 Package
Fully WEEE and RoHS Compliant
The SC4626 is a high efficiency, synchronous step-down
regulator providing up to 1A output current in a SOT235 package. The device requires only three external filter
components for a complete step-down regulator solution.
The input voltage range is 2.9 to 5.5V with either factory
programmed outputs from 1.0 to 3.3V or adjustable
output via an external resistor divider.
The converter operates at fixed 2.5MHz switching
frequency allowing small L/C filtering components.
The voltage mode architecture is compatible with chip
inductors and capacitors for minimum PCB footprint and
lowest overall system cost.
Up to 93% efficiency is achieved with low RDS(ON) internal
switches. PWM constant frequency operation ensures
low output ripple across the load range. 100% duty-cycle
provides 300mV dropout voltage at 1A which extends
the minimum input voltage for 2.5V and 3.3V outputs.
Excellent transient response is achieved with no external
compensation components.
The SC4626 provides input under-voltage, output overvoltage, output short circuit and over-temperature
protection to safeguard the device and system under fault
conditions. The regulator provides integrated soft-start to
minimize inrush currents. Standby quiescient current is
less than 1µA.
Applications
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Bluetooth Radios
DSC and PMPs
GPS Devices
xDSL Systems
POL Regulators
Portable HDD
Wireless LAN
The SC4626 is available in a SOT23-5 package.
Typical Application Circuit
VIN
2.9V to 5.5V
Enable
LX
VIN
CIN
10µF
VOUT
1.20V/1A
COUT
10µF
GND
EN
L
2.2µH
VOUT
SC4626C
April 23, 2009
www.semtech.com
SC4626
Pin Configuration
Ordering Information
(TOP VIEW)
VIN
1
GND
2
EN
3
5
4
LX
Device
Package & Description
SC4626xSKTRT(2)(3)(4)
SOT23-5
SC4626xEVB(5)
Evaluation Board - Standard
Size (i.e., Wire Wound Inductor)
SC4626xEVB-1(5)
Evaluation Board - Small Size
(i.e., Chip Inductor)
Notes:
(1) Measured in free convection, mounted on 10mm x 10mm, 2 layer FR4 PCB
shown in figure 4 with copper of 1oz for each layer.
(2) Available in tape and reel only. A reel contains 3,000 devices.
(3) Device is Pb-free, Halogen free, and RoHS/WEEE compliant.
(4) “x” is the code of the output voltage. See Table 1 for the code. For example,
the device number for VOUT= 1.20V is SC4626CSKTRT.
(5) “x” is the code of the output voltage. See Table 1 for the code. For example,
the EVB for VOUT= 1.20V is SC4626CEVB (Standard Size) or SC4626CEVB-1
(Small Size).
VOUT
SOT23-5
θJA = 90°C/W(1)
Marking Information
Table 1: Available Output Voltages
x
Code
VOUT(1)
A
1.00
C
1.20
E
1.28
F
1.30
H
1.50
L
1.80
Y
2.50
Z
3.30
Notes:
(1) Contact factory for unavaliable output voltage options.
Marking for SOT23, 5 Lead Package:
x = Code of the output voltage (Example: C for VOUT=1.20V)
yyww = Datecode (Example: 0852)
© 2009 Semtech Corp.
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SC4626
Recommended Operating Conditions
Absolute Maximum Ratings
VIN Supply Voltage ……………………………… -0.3 to 6.0V
VIN Supply Voltage ……………………………… 2.9 to 5.5V
LX Voltage …………..
Maximum Output Current
VOUT Voltage
-1 to VIN+1V, -3V (20ns Max), 6V Max
…………………………… 1.0A
……………………………… -0.3 to VIN+0.3V
EN Voltage …………………………………. -0.3 to VIN+0.3V
Thermal Information
Peak IR Reflow temperature …………………………. 260°C
ESD Protection Level
………………………………….
(2)
Thermal Resistance, Junction to Ambient(1) ………… 90°C/W
3kV
Operating Junction Temperature …………… -40 to +125˚C
Maximum Junction Temperature …………………… +150°C
Storage Temperature Range ………………… -65 to +150 °C
Exceeding the absolute maximum ratings may result in permanent damage to the device and/or device malfunction. Operation outside of the
parameters specified in the Electrical Characteristics section is not recommended.
Notes:
(1) Measured in free convection, mounted on 10mm x 10mm, 2 layer FR4 PCB shown in figure 4 with copper of 1oz for each layer.
(2) Tested according to JEDEC standard JESD22-A114-B.
Electrical Characteristics
Unless specified: VIN = 5.0V; -40°C<TA<+85 °C; TJ(MAX)=125°C; Unless otherwise noted typical values are TA=+25 °C.
Parameter
Symbol
Under-Voltage Lockout
UVLO
Output Voltage Tolerance
Conditions
Min
Typ
Max
Units
Rising VIN
2.60
2.70
2.80
V
Hysteresis
250
ΔVOUT
VIN=3.6V to 5.0V; No Load
-2.5
ILIMIT
Peak inductor current
1.5
IQ
EN= VIN, No Load
7.5
ISHDN
EN= GND
1
High Side Switch Resistance
RDSON_P
ILX= 100mA
0.15
Low Side Switch Resistance
RDSON_N
ILX= -100mA
0.125
VIN=5.5V; LX=0V; EN=GND
1
(1)
Current Limit
VIN Supply Current
VIN Shutdown Current
LX Leakage Current
ILK(LX)
VIN=5.5V; LX=5.0V; EN=GND
-10
mV
+2.5
%
A
mA
10
µA
Ω
10
-1
µA
Line Regulation
ΔVLINE-REG
VIN= 3.6 – 5.0V; IOUT=0A
±1.0
%
Load Regulation(2)
ΔVLOAD-REG
VIN= 5.0V; IOUT=10mA – 1.0A
±1.0
%
Oscillator Frequency
FOSC
Soft-Start Time(2)
TSS
2.0
2.5
3.0
100
MHz
µs
EN Input High Current
IEN_HI
EN=VIN
-2.0
2.0
µA
EN Input Low Current
IEN_LO
EN=GND
-2.0
2.0
µA
EN Input High Threshold
VEN_HI
EN Input Low Threshold
VEN_LO
© 2009 Semtech Corp.
1.2
V
0.4
V
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SC4626
Electrical Characteristics (continued)
Unless specified: VIN = 5.0V; -40°C<TA<+85 °C; TJ(MAX)=125°C; Unless otherwise noted typical values are TA=+25 °C.
Parameter
Symbol
VOUT Over Voltage Protection(2)
VOVP
Thermal Shutdown Temperature (2)
TSD
TSD_HYS
Thermal Shutdown Hysteresis (2)
Conditions
Min
Typ
Max
Units
115
%
Junction Temperature
+160
°C
Junction Temperature
10
°C
Notes:
(1) The “Output Voltage Tolerance” includes output voltage accuracy, voltage drift over temperature and the line regulation.
(2) Guaranteed by design.
© 2009 Semtech Corp.
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SC4626
Typical Characteristics
Circuit Conditions: VOUT=1.0V (SC4626A), 1.5V (SC4626H) & 3.3V (SC4626Z);CIN= 10uF/6.3V;COUT= 10uF/6.3V for L=2.2uH;COUT= 22uF/6.3V for L=1uH.
Unless otherwise noted, L= 2.2uH (TOKO: 1071AS-2R2M).
Efficiency
Efficiency vs. Load
Current (VOUT=3.3V)
Efficiency
Efficiency vs. Load
Current (VOUT=1.5V)
100%
100%
VIN= 4.0V
95%
VIN= 5.0V
90%
90%
85%
85%
Efficiency (%)
Efficiency (%)
95%
80%
75%
VIN= 3.3V
75%
70%
70%
VOUT= 1.50V
TA=25°C
65%
VIN= 5.0V
80%
VOUT= 3.30V
TA=25°C
65%
60%
60%
0.0
0.2
0.4
0.6
0.8
0.0
1.0
0.2
0.8
Efficiency
Efficiency vs. Load Current
(VIN=5.0V, VOUT=3.3V)
100%
100%
95%
90%
Efficiency (%)
L=1071AS-1R0N (33m_typ)
85%
80%
75%
L=MDT2520-CR1R0M (60m_typ)
70%
65%
85%
L=1071AS-1R0N (33m_typ)
80%
L=MDT2520-CR1R0M (60m_typ)
75%
70%
VIN= 5.0V
VOUT= 1.0V
TA=25°C
1.0
L=1071AS-2R2N (50m_typ)
L=1071AS-2R2N (50m_typ)
90%
Efficiency (%)
0.6
Efficiency
Efficiency vs. Load Current
(VIN=5.0V, VOUT=1.0V)
95%
VIN= 5.0V
VOUT= 3.3V
TA=25°C
65%
L=LQM2HPN1R0MG0
L=LQM2HP1R0MG0 (55m_typ)
60%
60%
0.0
0.2
0.4
0.6
0.8
0.0
1.0
0.2
Output Current (A)
Total Loss vs. LoadLosses
Current (VOUT=1.5V)
0.4
0.6
Output Current (A)
0.8
1.0
Total Loss vs. LoadLosses
Current (VOUT=3.3V)
500
500
VOUT= 1.50V
TA=25°C
VOUT= 3.30V
TA=25°C
400
400
VIN= 3.3V
300
Loss (mW)
Loss (mW)
0.4
Output Current (A)
Output Current (A)
200
VIN= 5.0V
100
300
VIN= 5.0V
200
100
VIN= 4.0V
0
0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
Output Current (A)
© 2009 Semtech Corp.
0.2
0.4
0.6
0.8
1.0
Output Current (A)
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SC4626
Typical Characteristics (continued)
Circuit Conditions: VOUT=1.0V (SC4626A), 1.5V (SC4626H) & 3.3V (SC4626Z);CIN= 10uF/6.3V;COUT= 10uF/6.3V for L=2.2uH;COUT= 22uF/6.3V for L=1uH.
Unless otherwise noted, L= 2.2uH (TOKO: 1071AS-2R2M).
(P &Temperature
N) Over Temperature
RRDSON
vs.
DS(ON)
RDSON (P& N) over Line
RDS(ON)
vs. Input Voltage
190
210
VIN= 5.0V
ILX= ±100mA
170
190
P-Channel
RDS(ON) (m)
RDS(ON) (m)
P-Channel
170
150
N-Channel
130
150
130
110
TA= 25°C
ILX= ±100mA
N-Channel
110
90
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40
-15
Input Voltage (V)
5%
60
85
1.0%
4%
0.8%
VOUT= 3.3V
3%
0.6%
2%
0.4%
1%
0.2%
Variation
Variation
35
Frequency
Variation
SwitchingSwitching
Frequency
vs. Temperature
Switching
Frequency vs.
Variation
over
Line
Switching
Frequency
Input
Voltage
0%
-1%
-2%
-0.2%
-0.6%
IOUT= 0A
TA= 25°C
-4%
0.0%
-0.4%
VOUT= 1.5V
-3%
VIN= 5.0V
IOUT= 0A
-0.8%
-5%
-1.0%
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40
-15
Input Voltage (V)
10
35
60
85
Ambient Temperature (°C)
Line Regulationvs.
over
Temperature
Line Regulation
Temperature
Line Regulation ove Line
Line
Regulation
1.0%
1.0%
0.8%
0.8%
0.6%
0.6%
VOUT= 1.5V
0.4%
0.4%
0.2%
Regulation
Regulation
10
Ambient Temperature (°C)
0.0%
-0.2%
0.2%
0.0%
-0.2%
-0.4%
-0.4%
VOUT= 3.3V
-0.6%
-0.6%
IOUT= 0A
TA= 25°C
-0.8%
VOUT= 1.5V
IOUT= 0A
-0.8%
-1.0%
-1.0%
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40
Input Voltage (V)
© 2009 Semtech Corp.
-15
10
35
60
85
Ambient Temperature (°C)
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SC4626
Typical Characteristics (continued)
Circuit Conditions: VOUT=1.0V (SC4626A), 1.5V (SC4626H) & 3.3V (SC4626Z);CIN= 10uF/6.3V;COUT= 10uF/6.3V for L=2.2uH;COUT= 22uF/6.3V for L=1uH.
Unless otherwise noted, L= 2.2uH (TOKO: 1071AS-2R2M).
Load Regulation
Load Regulation
(VOUT=3.3V)
Load Regulation
Load Regulation
(VOUT=1.5V)
1.0%
1.0%
VOUT= 1.50V
TA=25°C
0.6%
0.6%
0.4%
0.4%
0.2%
VOUT= 3.30V
TA=25°C
0.8%
Load Regulation
Load Regulation
0.8%
VIN= 3.3V
0.0%
-0.2%
-0.4%
VIN= 4.0V
0.2%
0.0%
-0.2%
-0.4%
VIN= 5.0V
-0.6%
VIN= 5.0V
-0.6%
-0.8%
-0.8%
-1.0%
-1.0%
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
Output Current (A)
1.0%
5%
0.8%
4%
0.6%
3%
0.4%
2%
0.2%
1%
Variation
Variation
0.6
0.8
1.0
60
85
Hysteresis Variation
UVLOUVLO
Hysteresis
Variation
Rising Threshold Variation
UVLOUVLO
Rising
Threshold Variation
0.0%
-0.2%
0%
-1%
-0.4%
-2%
-0.6%
-3%
-0.8%
0.4
Output Current (A)
-4%
IOUT= 0A
-1.0%
IOUT= 0A
-5%
-40
-15
10
35
60
85
-40
Ambient Temperature (°C)
-15
10
35
Ambient Temperature (°C)
Voltage
of 100%Duty
Duty Cycle
Operation
DropoutDropout
Voltage
in 100%
Cycle
Operation
400
TA= 25°C
Dropout Voltage (mV)
350
L= MDT2520-CR1R0M
(DCR= 60m_typ)
300
250
200
150
100
L= 1071AS-2R2N
(DCR=50m_typ)
50
0
0.0
0.2
0.4
0.6
0.8
1.0
Output Current (A)
© 2009 Semtech Corp.
www.semtech.com
SC4626
Typical Waveforms
Circuit Conditions: VOUT=1.5V (SC4626H); L= 2.2uH (TOKO: 1071AS-2R2M); CIN= COUT= 10uF/6.3V (Murata: GRM21BR60J106K).
Output
Voltage
Ripple
(V=1.5V)
OUT=1.5V)
Output
Voltage
Ripple
(VOUT
Output
Voltage
Ripple
(V=1.5V)
OUT=1.5V)
Output
Voltage
Ripple
(VOUT
VOUT
10mV/div
VOUT
10mV/div
ILX
ILX
500mA/div
500mA/div
VLX
VLX
2V/div
2V/div
VIN=5.0V
IOUT=0A
500ns/div
VIN=5.0V
IOUT=1.0A
4626-w1
Output
Voltage
Ripple
(V=1.5V)
OUT=1.5V)
Output
Voltage
Ripple
(VOUT
500ns/div
4626-w2
Output
Voltage
Ripple
(V=1.5V)
OUT=1.5V)
Output
Voltage
Ripple
(VOUT
VOUT
10mV/div
VOUT
10mV/div
ILX
ILX
500mA/div
500mA/div
VLX
VLX
2V/div
2V/div
VIN=3.3V
IOUT=0A
500ns/div
VIN=3.3V
IOUT=1.0A
4626-w3
(VOUT
TransientTransient
ResponseResponse
(VOUT=1.5V;
0A=1.5V)
to 0.5A)
500ns/div
4626-w4
Transient Response
OUT=1.5V)
Transient Response
(VOUT=1.5V;(V0.5A
to 1.0A)
VOUT
VOUT
100mV/div
100mV/div
IOUT
IOUT
500mA/div
500mA/div
VIN=5.0V
IOUT=0A to 0.5A
© 2009 Semtech Corp.
50µs/div
4626-w5
VIN=5.0V
IOUT=0.5A to 1A
50µs/div
4626-w6
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SC4626
Typical Waveforms (continued)
Circuit Conditions: VOUT=1.5V (SC4626H); L= 2.2uH (TOKO: 1071AS-2R2M); CIN= COUT= 10uF/6.3V (Murata: GRM21BR60J106K).
Up (VOUT=1.5V)
Start UpStart
(Enable)(V
=1.5V)
OUT
Up (VOUT=1.5V)
Start UpStart
(Enable)(V
=1.5V)
OUT
VIN
VIN
2V/div
2V/div
VEN
VEN
2V/div
2V/div
VOUT
VOUT
1V/div
1V/div
VIN=5.0V
ROUT=1k
VIN=5.0V
ROUT=1.5
100µs/div
Start
Up (Vup
=1.5V),
OUTV
Start Up
(Power
) (VOUTEN=VIN
=1.5V)
IN
100µs/div
Start
Up (Vup
=1.5V),
OUTV
Start Up
(Power
) (VOUTEN=VIN
=1.5V)
IN
VIN
VIN
2V/div
2V/div
VOUT
VOUT
500mV/div
500mV/div
VIN=5.0V
ROUT=1k
VIN=5.0V
ROUT=1.5
200µs/div
Start
UpUp
intointo
Pre-Biased
OUT=1.5V) Enable
Start
Pre-Bias Output
Output(V(Enable)
200µs/div
ShutdownShutdown-Disable
(Disable) (VOUT=1.5V)
VIN
2V/div
VIN
2V/div
VEN
2V/div
VEN
2V/div
VOUT
VOUT
500mV/div
500mV/div
VIN=5.0V
ROUT=1k
© 2009 Semtech Corp.
VIN=5.0V
ROUT=1.5
200µs/div
50µs/div
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SC4626
Typical Waveforms (continued)
Circuit Conditions: VOUT=3.3V (SC4626Z); L= 2.2uH (TOKO: 1071AS-2R2M); CIN= COUT= 10uF/6.3V (Murata: GRM21BR60J106K).
Output
Voltage
Ripple
(V=3.3V)
OUT=3.3V)
Output
Voltage
Ripple
(VOUT
Output
Voltage
Ripple
(V=3.3V)
OUT=3.3V)
Output
Voltage
Ripple
(VOUT
VOUT
10mV/div
VOUT
ILX
10mV/div
500mA/div
ILX
500mA/div
VLX
VLX
2V/div
2V/div
VIN=5.0V
IOUT=0A
500ns/div
VIN=5.0V
IOUT=1.0A
4626-w13
(VOUT
TransientTransient
ResponseResponse
(VOUT=3.3V;
0A=3.3V)
to 0.5A)
500ns/div
4626-w14
Transient Response
OUT=3.3V)
Transient Response
(VOUT=3.3V;(V0.5A
to 1.0A)
VOUT
VOUT
100mV/div
100mV/div
IOUT
IOUT
500mA/div
500mA/div
VIN=5.0V
IOUT=0A to 0.5A
50µs/div
VIN=5.0V
IOUT=0.5A to 1A
4626-w15
Up (VOUT=3.3V)
Start UpStart
(Enable)(V
=3.3V)
OUT
50µs/div
4626-w16
Up (VOUT=3.3V)
Start UpStart
(Enable)(V
=3.3V)
OUT
VIN
VIN
5V/div
5V/div
VEN
VEN
2V/div
2V/div
VOUT
VOUT
1V/div
1V/div
VIN=5.0V
ROUT=1k
© 2009 Semtech Corp.
VIN=5.0V
ROUT=3.3
200µs/div
10
200µs/div
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SC4626
Typical Waveforms (continued)
Circuit Conditions: VOUT=3.3V (SC4626Z); L= 2.2uH (TOKO: 1071AS-2R2M); CIN= COUT= 10uF/6.3V (Murata: GRM21BR60J106K).
Start
Up (Vup
=3.3V),
OUTV
Start Up
(Power
) (VOUTEN=VIN
=3.3V)
IN
Start
Up (Vup
=3.3V),
OUTV
Start Up
(Power
) (VOUTEN=VIN
=3.3V)
IN
VIN
VIN
2V/div
2V/div
VOUT
VOUT
1V/div
1V/div
VIN=5.0V
ROUT=1k
VIN=5.0V
ROUT=3.3
200µs/div
Start
Up Up
intointo
Pre-Biased
OUT=3.3V)(Enable)
Start
Pre-BiasOutput
Output(V(Enable)
VIN
200µs/div
Start
Pre-Biased
Output (Power
(VOUT=3.3V)(Power
Up)
StartUp
Upinto
into
Pre-Bias Output
Up V )
IN
VIN
2V/div
2V/div
VEN
2V/div
VOUT
VOUT
1V/div
1V/div
VIN=5.0V
ROUT=1k
VIN=5.0V
ROUT=1k
200µs/div
Shutdown-Disable
(VOUT
=3.3V)
Shutdown
(Disable) (VOUT
=3.3V)
200µs/div
Shutdown-Disable
(VOUT
=3.3V)
Shutdown
(Disable) (VOUT
=3.3V)
VIN
VIN
5V/div
5V/div
VEN
VEN
2V/div
2V/div
VOUT
VOUT
2V/div
2V/div
VIN=5.0V
ROUT=33
© 2009 Semtech Corp.
VIN=5.0V
ROUT=3.3
500µs/div
11
100µs/div
www.semtech.com
SC4626
Typical Waveforms (continued)
Circuit Conditions: VOUT=1.0V (SC4626A); L= 1.0uH (Murata: LQM2HPN1R0NG0L); CIN= 10uF/6.3V; COUT= 22uF/6.3V (Murata: GRM21BR60J226M).
Output
Voltage
Ripple
(V=1.0V)
OUT=1.0V)
Output
Voltage
Ripple
(VOUT
Output
Voltage
Ripple
(V=1.0V)
OUT=1.0V)
Output
Voltage
Ripple
(VOUT
VOUT
VOUT
10mV/div
10mV/div
ILX
ILX
500mA/div
Offset: 0A
500mA/div
VLX
VLX
2V/div
2V/div
VIN=3.3V
IOUT=0A
500ns/div
VIN=3.3V
IOUT=1.0A
4626-w25
Output
Voltage
Ripple
(V=1.0V)
OUT=1.0V)
Output
Voltage
Ripple
(VOUT
500ns/div
4626-w26
Output
Voltage
Ripple
(V=1.0V)
OUT=1.0V)
Output
Voltage
Ripple
(VOUT
VOUT
VOUT
10mV/div
10mV/div
ILX
ILX
500mA/div
1A/div
VLX
VLX
2V/div
2V/div
VIN=5.0V
IOUT=0A
500ns/div
VIN=5.0V
IOUT=1.0A
4626-w27
Transient
Response
(V=1.0V)
OUT=1.0V)
Transient
Response
(VOUT
500ns/div
4626-w28
Transient
Response
(V=1.0V)
OUT=1.0V)
Transient
Response
(VOUT
VOUT
VOUT
20mV/div
20mV/div
IOUT
IOUT
500mA/div
500mA/div
VIN=5.0V
IOUT=0A to 0.5A
© 2009 Semtech Corp.
50µs/div
4626-w29
12
VIN=5.0V
IOUT=0.5A to 1A
50µs/div
4626-w30
www.semtech.com
SC4626
Pin Descriptions
Pin #
Pin Name
1
VIN
Input power supplies. Powers the internal circuitry and is connected to the source of high-side P channel MOSFET.
2
GND
Ground connection.
3
EN
4
VOUT
5
LX
© 2009 Semtech Corp.
Pin Function
Enable pin. When connected to logic high or tied to VIN pin, the SC4626 is on. When connected to logic low, the
device enters shutdown and consumes less than 1µA of current. The enable pin has a 1 MΩ internal pulldown
resistor. This resistor is switched in circuit whenever the EN pin is below the enable input high threshold, or when
the part is in undervoltage lockout.
Output voltage sense pin.
Switching node - connect an inductor between this pin and the output capacitor.
13
www.semtech.com
SC4626
Block Diagram
VIN
+
Current Amp
Internal
Oscillator
VOVP
VOUT
Voltage
Select
Plimit
Comp
Plimit
Amp
Ramp
Generator
+
+
+
-
Control
Logic
OVP
Error Amp
LX
+
PWM
Comp
500mV
Ref
GND
EN
© 2009 Semtech Corp.
14
www.semtech.com
SC4626
Applications Information
adjusted to meet the equation shown above.
Detailed Description
The SC4626 is a synchronous step-down pulse width
modulated (PWM) voltage mode DC-DC regulator
operating at 2.5MHz fixed-frequency. The switching
frequency is chosen to minimize the size of the external
inductor and capacitors while maintaining high
efficiency.
Protection Features
The SC4626 provides the following protection features:
Thermal Shutdown
Current Limit
Over-Voltage Protection
Soft-Start Operation
•
•
•
•
Operation
During normal operation, the internal highside PMOS device is activated on each rising edge of the internal oscillator.
The voltage
feedback loop uses an internal feedback resistor divider.
The period is set by the on board oscillator when in PWM
mode at average to high loads. The device has an internal
low-side synchronous NMOS device and does not require a
Schottky diode on the LX pin. The device operates as a buck
converter in PWM mode with a fixed frequency of 2.5MHz.
Thermal Shutdown
The device has a thermal shutdown feature to protect
the SC4626 if the junction temperature exceeds 160°C.
During thermal shutdown, the on-chip power devices
are disabled with the LX output floating. When the die
temperature drops by 10°C, the part will initiate a soft
start recovery to normal operation.
Current Limit
The internal PMOS power device in the switching stage is
protected by current limit feature. If the output is loaded
above the PMOS current limit for 32 consecutive cycles,
the SC4626 enters foldback current limit mode and the
output current is limited to the current limit holding
current (ICL_HOLD) of a few hundred milliampere. Under
these conditions the output voltage will be the product
of I CL_HOLD and the load resistance. The current limit
holding current (ICL_HOLD) will be decreased when output
voltage is increased. The load presented must fall below
the current limit holding current for the SC4626 to exit
foldback current limit mode. Figure 2 shows the typical
current limit holding current decreasing rate over different output voltage. The SC4626 is capable of sustaining
a indefinite short circuit without damage and will resume
normal operation when the fault is removed. The foldback current limit mode will be disabled during the
Current Limit Holding Current over Vout
soft-start.
C FF [nF ] = 10 ×
(VOUT − 0.5)2
VOSTD
×(
)
RFB1[kΩ] ⋅ (VOUT − VOSTD ) VOSTD − 0.5
,where the VOSTD is the standard voltage shown in Table 1.
To simplify the design, it is recommended to program the
desired output voltage from standard 1.0V as shown in
Figure 1 with a proper CFF calculated from the equation
Schematic of Adjustable VOUT from SC4626A (Std VOUT=1.0V)
shown above. For programming the output voltage from
other standard voltage, the RFB1, RFB2 and CFF need to be
L
VIN
VIN
VOUT
LX
CIN
REN
COUT
GND
RFB1
Enable
EN
CFF
150
TA= 25°C
Current Limit holding Current (mA)
Output Voltage Selection
The SC4626 is designed for fixed output voltage. There
are some options for preset output voltage shown in
Table 1. If the voltage desired is not shown in the Table
1, it can be programmed via an external resistor divider. There will be typical 1uA current flowing into the
VOUT pin. The typical schematic of adjustable output
voltage option from the part with standard 1.0V, the
SC4626A, is shown in Figure 1. The CFF is needed for
maintain the performance of the transient response. The
proper value of CFF can be calculated by the equation
120
VIN= 5.0V
90
60
30
VIN= 3.6V
VOUT
SC4626A
RFB2
10k
0
RFB1 = (VOUT − 1) × RFB 2
1.0
1.5
2.0
2.5
3.0
3.5
Output Voltage (V)
Figure 1 — Typical schematic for adjustable output
voltage option from standard 1.0V of SC4626A
Note: (1) REN is optional.
© 2009 Semtech
Corp.
and C
(2) R =10k
FB2
=10nF for standard design.
FF
Figure 2 — Current limit holding current decreasing
rate vs. output voltage
15
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SC4626
Applications Information (continued)
Over-Voltage Protection
In the event of a 15% over-voltage on the output, the
PWM drive is disabled with LX pin floating.
of output filter can be defined by the equation
fC
Soft-Start
The soft-start mode is activated after VIN reaches its
UVLO and EN signal is set high to enable the part. An over
temperature shutdown event will also activate the soft
start sequence. Soft-start mode controls the maximum
current during startup thus limiting in-rush current. The
PMOS current limit is stepped through four soft start
levels of approximately 20%, 25%, 40%, & 100%. Each
step is maintained for 20μs following internal reference
start up of 20μs giving the total nominal startup period
of 100μs. During startup, the chip operates in controlling
the inductor current swings between 0A and current
limit. If VOUT reaches 90% of the target within the first 2
current levels, the chip continues in hysteretic mode till
the end of the soft-start time period before switching to
PWM mode. If VOUT does not reach 90% by the end of the
second current limit level, soft start will continue to level 3
or level 4 till the output voltage reaches 96% and will then
transition into PWM mode. After the full soft start time
period, the SC4626 will switch into PWM mode operation
regardless of the VOUT level.
1
2S L ˜ COUT
Values outside this range may lead to instability,
malfunction, or out-of-specification performance.
When choosing an inductor, it is important to consider
the change in inductance with DC bias current. The
inductor saturation current is specified as the current at
which the inductance drops a specific percentage from
the nominal value. This is approximately 30%. Except for
short-circuit or other fault conditions, the peak current
must always be less than the saturation current specified
by the manufacturer. The peak current is the maximum
load current plus one half of the inductor ripple current at
the maximum input voltage. Load and/or line transients
can cause the peak current to exceed his level for short
durations. Maintaining the peak current below the
inductor saturation specification keeps the inductor ripple
current and the output voltage ripple at acceptable levels.
Manufacturers often provide graphs of actual inductance
and saturation characteristics versus applied inductor
current. The saturation characteristics of the inductor can
vary significantly with core temperature. Core and ambient
temperatures should be considered when examining the
core saturation characteristics.
The SC4626 is capable of starting up into a pre-biased
output. When the output is precharged by another supply
rail, the SC4626 will not discharge the output during the
soft start interval.
Shut Down
When the EN pin voltage goes low, the SC4626 will run in
shutdown mode, drawing less than 1μA from the input
power supply. The internal switches and bandgap voltage
will be immediately turned off.
When the inductance has been determined, the DC
resistance (DCR) must be examined. The efficiency that
can be achieved is dependent on the DCR of the inductor.
The lower values give higher efficiency. The RMS DC
current rating of the inductor is associated with losses in
the copper windings and the resulting temperature rise of
the inductor. This is usually specified as the current which
produces a 40˚C temperature rise. Most copper windings
are rated to accommodate this temperature rise above
maximum ambient.
Inductor Selection
The SC4626 converter has internal loop compensation.
The compensation is designed to work with a output filter
corner frequency is less than 100kHz over any operating
condition, tolerance and bias effect. The corner frequency
Magnetic fields associated with the output inductor can
interfere with nearby circuitry. This can be minimized by
the use of low noise shielded inductors which use the
minimum gap possible to limit the distance that magnetic
fields can radiate from the inductor. However shielded
inductors typically have a higher DCR and are thus less
efficient than a similar sized non-shielded inductor.
© 2009 Semtech Corp.
16
www.semtech.com
SC4626
Applications Information (continued)
Vout Code (Vout)
A(1.0V),C(1.2V),E(1.28V),F(1.3V),H(1.5V)
Inductor
Output Capacitor
Description
Vender
Part Number
Description
Vender
Part Number
Qty.
2.2uH,
60m(max)
Wire Wound
2.8x3.0x1.5(mm)
TOKO
1071AS-2R2M
10uF,6.3V
X5R,0805
Murata
GRM21BR60J106K
1
1.0uH,
40m(max)
Wire Wound
2.8x3.0x1.5(mm)
TOKO
1071AS-1R0N
22uF,6.3V
X5R,0805
Murata
GRM21BR60J226M
1
2.2uH,
120m(max)
Wire Wound
2.5x2.0x1.2(mm)
TOKO
1222AS-H-2R2M
10uF,6.3V
X5R,0805
Murata
GRM21BR60J106K
1
22uF,6.3V
X5R,0805
Murata
GRM21BR60J226M
1
10uF,6.3V
X5R,0805
Murata
GRM219R60J106K
1
22uF,6.3V
X5R,0805
Murata
GRM21BR60J226M
1
10uF,4.0V
X5R,0603
Murata
GRM188R60G106M
2
1.0uH,
80m(max)
Multilayer Chip
2.5x2.0x1.0(mm)
1.0uH,
69m(max)
Multilayer Chip
2.5x2.0x1.0(mm)
TOKO
Murata
MDT2520-CR1R0M
LQM2HPN1R0MG0
Table 2a – Recommended L and output capacitors for Vout=1.0V to 1.5V
Vout Code (Vout)
L(1.8V),Y(2.5V),Z(3.3V)
Inductor
Output Capacitor
Description
Vender
Part Number
Description
Vender
Part Number
Qty.
2.2uH,
60m(max)
Wire Wound
2.8x3.0x1.5(mm)
TOKO
1071AS-2R2M
10uF,6.3V
X5R,0805
Murata
GRM21BR60J106K
1
1.0uH,
40m(max)
Wire Wound
2.8x3.0x1.5(mm)
TOKO
1071AS-1R0N
22uF,6.3V
X5R,0805
Murata
GRM21BR60J226M
1
2.2uH,
120m(max)
Wire Wound
2.5x2.0x1.2(mm)
TOKO
1222AS-H-2R2M
10uF,6.3V
X5R,0805
Murata
GRM21BR60J106K
1
22uF,6.3V
X5R,0805
Murata
GRM21BR60J226M
1
10uF,4.0V
X5R,0603
Murata
GRM188R60G106M
2
1.0uH,
80m(max)
Multilayer Chip
2.5x2.0x1.0(mm)
TOKO
MDT2520-CR1R0M
Table 2b – Recommended L and output capacitors for Vout=1.8V to 3.3V
© 2009 Semtech Corp.
17
www.semtech.com
SC4626
Applications Information (continued)
Capacitors with X7R or X5R ceramic dielectric are recommended for their low ESR and superior temperature and
voltage characteristics. Y5V capacitors should not be used
as their temperature coefficients make them unsuitable
for this application.
The SC4626 is compatible with small shielded chip
inductors for low cost, low profile applications. The
inductance roll off characteristic of chip inductor is worse
resulting in high ripple current and increased output
voltage ripple at heavy load operation. SC4626 has OCP
peak inductor current threshold of 1.5A minimum, to
support 1A DC load current, the inductor ripple current at
1A DC load current needs to be less than 1A.
The output voltage droop due to a load transient is determined by the capacitance of the ceramic output capacitor.
The ceramic capacitor supplies the load current initially
until the loop responds. Within a few switching cycles the
loop will respond and the inductor current will increase to
match the required load. The output voltage droop during
the period prior to the loop responding can be related to
the choice of output capacitor by the relationship
Final inductor selection depends on various design
considerations such as efficiency, EMI, size, and cost.
Table 2a and 2b list the manufacturers of recommended
inductor and output capacitors options. Chip inductors
provide smaller footprint and height with lower efficiency
and increased output voltage ripple. Transient load
performance is equivalent to wire wound inductors.
Figure 3 shows the typical efficiency curves for different
inductors.
COUT =
3 ⋅ ∆I LOAD
VDROOP ⋅ f OSC
Efficiency
The output capacitor RMS current ripple may be calculated
from the equation
100%
L=1071AS-2R2N (50m_typ)
95%
Efficiency (%)
90%
I COUT ( RMS ) =
85%
L=1071AS-1R0N (33m_typ)
1  VOUT ⋅ (VIN ( MAX ) − VOUT )


L ⋅ f OSC ⋅ VIN
2 3 

80%
L=MDT2520-CR1R0M (60m_typ)
75%
70%
VIN= 5.0V
VOUT= 3.3V
TA=25°C
65%
Table 3 lists the manufacturers of recommended output
capacitor options.
L=LQM2HP1R0MG0 (55m_typ)
CIN Selection
The SC4626 source input current is a DC supply current
with a triangular ripple imposed on it. To prevent large
input voltage ripple, a low ESR ceramic capacitor is
required. A minimum value of 4.7μF should be used. It is
important to consider the DC voltage coefficient characteristics when determining the actual required value. To
estimate the required input capacitor, determine the
acceptable input ripple voltage and calculate the
minimum value required for CIN from the equation
60%
0.0
0.2
0.4
0.6
Output Current (A)
0.8
1.0
Figure 3 — Typical efficiency curves
(VIN=5.0V, VOUT=3.3V)
COUT Selection
The internal voltage loop compensation in the SC4626
limits the minimum output capacitor value to 10µF if
using the inductor of 2.2µH. This is due to its influence
on the the loop crossover frequency, phase margin, and
gain margin. Increasing the output capacitor above this
minimum value will reduce the crossover frequency and
provide greater phase margin. A total output capacintance
should not exceed 30uF to avoid any start-up problems.
For most typical applications, it is recommended to use
output capacitance of 10uF to 22uF. When choosing
output capacitor’s capacitance, verify the voltage derating
effect from the capacitor vendors data sheet.
© 2009 Semtech Corp.
C IN
 VOUT 
1 −

VIN 

=

 ∆V

− ESR  ⋅ f OSC
I
 OUT

VOUT
VIN
The input capacitor RMS ripple current varies with the
18
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SC4626
Applications Information (continued)
input and output voltage. The maximum input capacitor
RMS current is found from the equation
I CIN ( RMS ) =
VOUT
VIN
 VOUT
1 −
VIN




The input voltage ripple and RMS current ripple are at
maximum when the input voltage is twice the output
voltage or 50% duty cycle.
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the PMOS switch.
Low ESR/ESL X5R ceramic capacitors are recommended
for this function. To minimise stray inductance ,the
capacitor should be placed as closely as possible to the
VIN and GND pins of the SC4626.
Type
Rated
Voltage
(VDC)
Value
at
3.3V
(μF)
Dimensions
LxWxH
(mm)
10±10%
X5R
10
4.42
2.0x1.25x1.25
(EIA:0805)
Murata
GRM21BR71A106K
10±10%
X7R
10
4.88
2.0x1.25x1.25
(EIA:0805)
Murata
GRM21BR60J106K
10±10%
X5R
6.3
4.05
2.0x1.25x1.25
(EIA:0805)
Murata
GRM21BR70J106K
10±10%
X7R
6.3
4.91
2.0x1.25x1.25
(EIA:0805)
Murata
GRM21BR60J226M
22±20%
X5R
6.3
6.57
2.0x1.25x1.25
(EIA:0805)
Manufacturer
Part Nunber
Value
(μF)
Murata
GRM21BR61A106K
Table 3 – Recommended Capacitors
© 2009 Semtech Corp.
19
www.semtech.com
SC4626
Applications Information (continued)
PCB Layout Considerations
The layout diagram in Figure 4 shows a recommended PCB
top-layer and bottom layer for the SC4626 and supporting
components. Fundamental layout rules must be followed
since the layout is critical for achieving the performance
specified in the Electrical Characteristics table. Poor layout
can degrade the performance of the DC-DC converter
and can contribute to EMI problems, ground bounce, and
resistive voltage losses. Poor regulation and instability
can result.
L
CIN
The following guidelines are recommended when
developing a PCB layout:
. The input capacitor, CIN should be placed as close to the
VIN and GND pins as possible. This capacitor provides
a low impedance loop for the pulsed currents present
at the buck converter’s input. Use short wide traces
to connect as closely to the IC as possible. This will
minimize EMI and input voltage ripple by localizing
the high frequency current pulses.
2. Keep the LX pin traces as short as possible to minimize
pickup of high frequency switching edges to other
parts of the circuit. COUT and L should be connected as
close as possible between the LX and GND pins, with
a direct return to the GND pin from COUT.
3. Route the output voltage feedback/sense path away
from inductor and LX node to minimize noise and
magnetic interference.
4. Use a ground plane referenced to the SC4626 GND
pin. Use several vias to connect to the component
side ground to further reduce noise and interference
on sensitive circuit nodes.
5. If possible, minimize the resistance from the VOUT and
GND pins to the load. This will reduce the voltage drop
on the ground plane and improve the load regulation.
And it will also improve the overall efficiency by
reducing the copper losses on the output and ground
planes.
© 2009 Semtech Corp.
VOUT
COUT
U1
GND
VIN
(a) Top layer
GND
EN
(b) Bottom layer
Figure 4 — Recommended PCB
Top & Bottom Layer Layout
20
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SC4626
Outline Drawing – SOT23-5
A
e1
2X E/2
ccc C
DIM
D
A
A1
A2
b
c
D
E1
E
e
e1
L
L1
N
01
aaa
bbb
ccc
N
EI
1
E
2
2X N/2 TIPS
e
B
D
aaa C
A2
DIMENSIONS
INCHES
MILLIMETERS
MIN NOM MAX MIN NOM MAX
.035
.000
.035
.010
.003
.110
.060
-
.045
-
.057
.006
.051
.020
.009
.118
.069
.114
.063
.110 BSC
.037 BSC
.075 BSC
.012 .018 .024
(.024)
5
0°
10°
.004
.008
.008
0.90
0.00
.90
0.25
0.08
2.80
1.50
-
1.15
-
1.45
0.15
1.30
0.50
0.22
3.00
1.75
2.90
1.60
2.80 BSC
0.95 BSC
1.90 BSC
0.30 0.45 0.60
(0.60)
5
0°
10°
0.10
0.20
0.20
A
SEATING PLANE
A1
C
H
bxN
bbb
C A-B D
c
GAGE
PLANE
0.25
L
01
(L1)
SEE DETAIL
DETAIL
A
A
SIDE VIEW
NOTES:
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
OR GATE BURRS.
Land Pattern – SOT23-5
X
DIM
(C)
G
Z
Y
P
C
G
P
X
Y
Z
DIMENSIONS
INCHES
MILLIMETERS
(.098)
.055
.037
.024
.043
.141
(2.50)
1.40
0.95
0.60
1.10
3.60
NOTES:
1.
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
Contact Information
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Fax: 81-3-6408-0951
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Tel: 82-2-527-4377
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Tel: 49-(0)8161-140-12300
Fax: 49-(0)8161-140-124
Semtech International AG is a wholly-owned subsidiary of Semtech
Corporation, which has its headquarters in the U.S.A.
www.semtech.com
© 2009 Semtech Corp.
21
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SC4626
© Semtech 2010
All rights reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner.
The information presented in this document does not form part of any quotation or contract, is believed to be accurate
and reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its
use. Publication thereof does not convey nor imply any license under patent or other industrial or intellectual property
rights. Semtech assumes no responsibility or liability whatsoever for any failure or unexpected operation resulting from
misuse, neglect improper installation, repair or improper handling or unusual physical or electrical stress including, but
not limited to, exposure to parameters beyond the specified maximum ratings or operation outside the specified range.
SEMTECH PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED OR WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT
APPLICATIONS, DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF SEMTECH PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE UNDERTAKEN SOLELY AT THE CUSTOMER’S OWN RISK. Should a customer purchase or use
Semtech products for any such unauthorized application, the customer shall indemnify and hold Semtech and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs damages and attorney fees which could arise.
Contact Information
Taiwan Branch
Tel: 886-2-2748-3380
Fax: 886-2-2748-3390
Semtech Switzerland GmbH
Japan Branch
Tel: 81-3-6408-0950
Fax: 81-3-6408-0951
Korea Branch
Tel: 82-2-527-4377
Fax: 82-2-527-4376
Semtech Limited (U.K.)
Tel: 44-1794-527-600
Fax: 44-1794-527-601
Shanghai Office
Tel: 86-21-6391-0830
Fax: 86-21-6391-0831
Semtech France SARL
Tel: 33-(0)169-28-22-00
Fax: 33-(0)169-28-12-98
Semtech Germany GmbH
Tel: 49-(0)8161-140-12300
Fax: 49-(0)8161-140-124
Semtech International AG is a wholly-owned subsidiary of Semtech
Corporation, which has its headquarters in the U.S.A.
www.semtech.com
© 2009 Semtech Corp.
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