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1.5 MHz, 600mA Synchronous Step-Down Converter With Low Quiescent Current
Product Description
GS5571 is a 1.5Mhz constant frequency, slope compensated current mode PWM step-down converter. The device integrates a main switch and a synchronous rectifier for high efficiency without an external Schottky diode. It is ideal for powering portable equipment that runs from a single cell lithium-Ion (Li+) battery. The GS5571 can supply 600mA of load current from a 2.5V to 5.5V input voltage. The output voltage can be regulated as low as 0.6V. The GS5571 can also run at 100% duty cycle for low dropout operation, extending battery life in portable system. Idle mode operation at light loads provides very low output ripple voltage for noise sensitive applications. The GS5571 is offered in a low profile (1mm) 5-pin, thin SOT package, and is available in an adjustable version and fixed output voltage of 1.2V, 1.5V and 1.8V
Features
High Efficiency: Up to 96%. 1.5Mhz Constant Switching Frequency. 600mA Output Current at VIN=3.0V. Integrated Main switch and synchronous rectifier. No Schottky Diode Required. 2.5V to 5.5V Input Voltage Range. Output Voltage as Low as 0.6V. 100% Duty Cycle in Dropout. Low Quiescent Current: 30A. <1uA Shutdown Current. Slope Compensated Current Mode Control for Excellent Line and Load Transient Response. Short Circuit and Thermal Fault Protection Space Saving 5-Pin Thin SOT23 package.
Applications
Cellular and Smart Phones PDAs MP3 Player DSP Core Supplies Digital Still Cameras Portable instruments
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Block Diagram
OSC SLOPE COMP VIN 2.7-5.5V ISENCE COMP + Vin
BLANKING SQ 0.6V VFB/ VOUT + EA +
COMP
X
RQ PWM RS LATCH +
DRV LOGIC
NONOVERLAP CONTROL
VOUT SW R1 COUT
R1 0.65V
OVDET
R2 VIN 0.6V SHUTDOWN
+ IZERO COMP GND
R2
RUN
Vref
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Packages & Pin Assignments
Adjustable Version Pin No. Fixed Version Pin No. Symbol
1 2
GS5571L-xxF
Description
Enable (Active High) Ground Switch Input Feedback Output
5
4
1 2
5
4
RUN GND SW VIN FB VOUT
GS5571LF
3 4
3 4
1
2
3
5 -
1
2
3
5
Ordering Information
GS Brand Name Part Number
GS 5571 P xx F
Package Code Voltage Code Pb Free Code
GS Complete P/N
GS5571LF GS5571L12F
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Voltage
Adjustable 1.2V 1.5V 1.8V
Package
SOT-23-5L SOT-23-5L SOT-23-5L SOT-23-5L
Marking
DAAYWG DADYWG DAGYWG DAFYWG
Q' / Reel ty
3000 Pcs 3000 Pcs 3000 Pcs 3000 Pcs
GS5571L18F
Adjustable Version need not Voltage Code.
Marking Information
GS P/N Voltage Code
DA V YW G
Date Code GS Code
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Absolute Maximum Ratings
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied.
Parameter
Symbol
Max
Units
Input Supply Voltage VIN -0.3V to 6 V Enable, Feedback Voltages VRUN,VFB .-0.3 to VIN+0.3 V SW Voltages VSW, -0.3 to VIN+0.3 V Peak SW Sink and Source Current IPSW , 1.5 A Operating Temperature Range (Note 2) TA -40 to +85 C Operating Junction Temperature Range TJ +125 C Storage Temperature Range TSTG -65 to +150 C Lead Temperature (Soldering) 10 Sec. TLEAD 300 C ESD Rating (Human Body Model) ESD 2 kV Note 1Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + PD x JA
Electrical Characteristics (Note 3)
(VIN =VRUN = 3.6V, TA = 25C, unless otherwise noted)
Parameter
Input Voltage Range Input DC Supply Current Active Mode Shutdown Mode Regulated Feedback Voltage VFB Input Bias Current Reference Voltage Line Regulation Regulated www..com Output Voltage Output Voltage Line Regulation Output Voltage Load Regulation Maximum Output Current Oscillator Frequency RDS(ON) of P-CH MOSFET RDS(ON) of N-CH MOSFET Peak Inductor Current SW Leakage Output over voltage lockout RUN Threshold RUN Leakage Current
Conditions
VFB = 0.5V VFB = 0V, VIN = 4.2V TA = +25C TA = 0C TA 85C TA = -40C TA 85C VFB = 0.65V VIN = 2.5V to 5.5V, VOUT = VFB (R2=0) GS5571-1.2, -40C TA 85C GS5571-1.5, -40C TA 85C GS5571-1.8, -40C TA 85C VIN = 2.5V to 5.5V, IOUT = 10mA IOUT from 0 to 600mA VIN = 3.0V VFB = 0.6V or VOUT = 100% ISW = 300mA ISW = -300mA VIN = 3V, VFB = 0.5V or VOUT = 90% Duty Cycle < 35% VRUN =0V, VSW = 0V or 5V, VIN = 5V VOVL = VOVL - VFB -40C TA 85C
MIN
2.5 0.5880 0.5865 0.5850 1.164 1.455 1.746 600 1.2 0.3
TYP
270 0.08 0.6000 0.6000 0.6000 0.11 1.200 1.500 1.800 0.11 0.0015 1.5 0.30 0.20 1.20 0.01 60 0.45 0.1
MAX
5.5 400 1.0 0.6120 0.6135 0.6150 30 0.40 1.236 1.545 1.854 0.40 1.8 0.50 0.45
unit
V A A V V V nA %/V V V V %/V %/mA mA MHz . A
1 1.30 1
A mV V A
Note 3: 100% production test at +25C. Specifications over the temperature range are guaranteed by design and characterization.
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Typical Applications
L1
Vout
L
Vout
Vin
Vin SW R2 Ccomp Cout
Vin
Vin
SW
Cout
GS5571
Cin RUN GND FB R1
Cin
GS5571-xx
RUN GND VOUT
VOUT = VREF x ( 1 + R2/R1 ) Adjustable Voltage Version Fixed Voltage Version
Typical Performance Characteristics
Efficiency vs Input Voltage
100 95 90
EFFICIENCY (%)
Efficiency vs Output Current
100 90 VIN = 2.7V 80 70 60 50 40 30 VIN = 4.2V VIN = 3.6V
100mA
85
EFFICIENCY (%)
80 75 70 65 60 55 TA = 25C VOUT = 1.8V 10mA 500mA
20 10
VOUT = 1.2V TA = 25C
50 www..com 2 2.5 3 3.5 4 4.5 5 5.5 6
INPUT VOLTAGE (V)
0 0.1
1 10 100 OUTPUT CURRENT (mA)
1000
Efficiency vs Load Current
100 95 90 85
EFFICIENCY (%) EFFICIENY (%)
Efficiency vs Load Current
100 95 2.7V
2.7V
90 85 80 75 70 65 60 55 50 45 3.6V TA = 25C Vout = 1.8V 4.2V
80 75 70 65 60 55 50 45 40 0.1 1 10 100 1000 TA = 25C Vout = 1.5V 3.6V 4.2V
40 0.1
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
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Typical Performance Characteristics (Continue)
Efficiency vs Load Current
100 95 90 85
EFFICIENCY (%)
2.7V
80 75 70 65 60 55 50 45 40 0.1 1 10 3.6V
4.2
TA = 25C Vout = 2.5V
100
1000
LOAD CURRENT (mA)
Outpu Voltage vs Load Current
1.84 1.82 1.8
OUTPUT VOLTAGE (V) FREQUENCY (MHz)
Frequency vs Input Voltage
1.46 1.45 1.44 1.43 1.42 1.41 1.4 1.39 1.38 1.37 VOUT = 1.8V ILOAD = 150mA L = 2.2uH
1.78 1.76 1.74 1.72 1.7 1.68 1.66 VOUT = 1.8V VIN = 3.6V L = 2.2uH
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0 200 400 600 800 1000 1200
LOAD CURRENT (mA)
1.36 2.7
3.15
3.6
4.05
4.5
4.95
5.4
INPUT VOLTAGE (V)
RDS(ON) vs Input Voltage
0.50 0.45 0.40
R DS(ON) (ohm)
Reference Voltage vs Temperature
0.6080 0.6072
REFERENCE VOLTAGE (V)
VIN = 3.6V
0.6064 0.6056 0.6048 0.6040 0.6032 0.6024 0.6016 0.6008 -50
0.35 0.30 0.25 0.20
MAIN SWITCH
SYNCHRONOUS SWITCH 0.15 0.10 1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
-30
-10
10
30
50
70
90
INPUT VOLTAGE (V)
TEMPERATURE (C)
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Typical Performance Characteristics (Continue)
RDS(ON) vs Temperature
0.38 0.36 0.34 VIN = 3.6V
Input Voltage vs Input Current
0.32 0.32 0.31
INPUT CURRENT (mA)
VOUT = 1.8V ILOAD = 0 L = 2.2uH
0.32
RDS(ON) (OHM)
0.31 0.30 0.29 0.29 0.28 0.28 0.27
N_RDS(ON) 0.30 0.28 0.26 0.24 0.22 P_R DS(ON) 0.20 0.18 -45 -30 -15 0 15 30 45 Temperature (C) 60 75 90
0.26 2.7
3
3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4 5.7 INPUT VOLTAGE (V)
Frequency vs Temperature
1.60 1.55 1.50
OSC Frequency (MHz) Supply Current (uA)
Supply Current vs Temperature
320
VIN = 3.6V 300
1.45 1.40 1.35 1.30 1.25 1.20 1.15
280
260
240
220
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-25
0
25
50
75
100
200 -50
-30
-10
10
30
50
70
90
Temperature (C)
Temperature (C)
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Operation
GS5571 is a monolithic switching mode Step-Down DC-DC converter. It utilizes internal MOSFETs to achieve high efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a fixed switching frequency, and uses the slope compensated current mode architecture. This Step-Down DC-DC Converter supplies 600mA output current at VIN = 3V with input voltage range from 2.5V to 5.5V.
Current Mode PWM Control
Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for excellent load and line responses and protection of the internal main switch (P-Ch MOSFET) and synchronous rectifier (N-Ch MOSFET). During normal operation, the internal P-Ch MOSFET is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. The current comparator, ICOMP, limits the peak inductor current. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indicated by the current reversal comparator, IZERO, or the beginning of the next clock cycle. The OVDET comparator controls output transient overshoots by turning the main switch off and keeping it off until the fault is no longer present.
Idle Mode Operation
At very light loads, the GS5571 automatically enters Idle Mode. In the Idle Mode, the inductor current may reach zero or reverse on each pulse. The PWM control loop will automatically skip pulses to maintain output regulation. The bottom MOSFET is turned off by the current reversal comparator, IZERO, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator.
Dropout Operation
When the input voltage decreases toward the value of the output voltage, the GS5571 allows the main switch to (Note 5) remain on for more than one switching cycle and increases the duty cycle until it reaches 100%. The output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-Channel MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure the heat dissipated not to exceed the maximum junction temperature of the IC. Note 5: The duty cycle D of a step-down converter is defined as:
VOUT D = TON x fOSC x 100% ~ ~ x100% VIN
Where TON is the main switch ON time, and fOSC is the oscillator frequency (1.5Mhz). The output voltage then is
the input voltage minus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-Channel MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure the heat dissipated not to exceed the maximum junction www..com temperature of the IC. Maximum Load Current
The GS5571 will operate with input supply voltage as low as 2.5V, however, the maximum load current decreases at lower input due to large IR drop on the main switch and synchronous rectifier. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty cycle decreases.
Layout Guidance
When laying out the PC board, the following suggestions should be taken to ensure proper operation of the GS5571. These items are also illustrated graphically in Figure 3. 1. The power traces, including the GND trace, the SW trace and the VIN trace should be kept short, direct and wide. 2. The VFB pin should be connected directly to the feedback resistor. The resistive divider R1/R2 must be connected between the (+) plate of C3 and ground. 3. Connect the (+) plate of C1 to the VIN pin as closely as possible. This capacitor provides the AC current to internal power MOSFET. 4. Keep the switching node, SW, away from the sensitive VFB node. 5. Keep the (-) plates of C1 and C3 as close as possible.
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Operation (Continue)
L1
Vout
Vin
Vin SW R2 C2 C3
GS5571B
C1 RUN GND FB R1
GS5571 Layout Example
Setting the Output Voltage
Figure 1 shows the basic application circuit with GS5571 adjustable output version. The external resistor sets the output voltage according to the following equation:
VOUT = 0.6V x ( 1 + R2 ) R1
VOUT 1.2V 1.5V 1.8V 2.5V
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R1 316k 316k 316k 316k
R2 316k 470k 634k 1000k
Table 1.
Resistor select for output voltage setting
Inductor Selection
For most designs, the GS5571 operates with inductors of 1H to 4.7H. Low inductance values are physically smaller but require faster switching, which results in some efficiency loss. The inductor value can be derived from the following equation:
L=
V OUT x (VVIN - VOUT) OUT V IN x IL X fOSC
Where IL is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high ripple currents. Choose inductor ripple current approximately 35% of the maximum load current 600mA, or IL = 210mA. For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is 2.2H. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the 50m to 150m range. For higher efficiency at heavy loads (above 200mA), or minimal load regulation (but some transient overshoot), the resistance should be kept below 100m.. The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation (600mA+105mA).
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Operation (Continue)
Input Capacitor Selection
The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input capacitor impedance at the switching frequency shall be less than input source impedance to prevent high frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. A 4.7F ceramic capacitor for most applications is sufficient.
Output Capacitor Selection
The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current. The output ripple VOUT is
determined by:
VOUT =
VOU T x (VIN - VOU T) VIN x L X fOSC
x( ESR +
1 8 x C3 x f OSC
)
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Package Dimension
SOT-23-5L PLASTIC PACKAGE
D e1
E E1
G
L e b (L1)
A
A2 A1
c
Dimensions
SYMBOL
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Millimeters MIN MAX
0.95 0.05 0.90 0.30 0.08 2.80 2.60 1.50 0.95 (TYP) 1.90 (TYP) 0.35 0.60 (TYP) 0.25 (TYP) 0 8 0.55 1.45 0.15 1.30 0.50 0.20 3.00 3.00 1.70
Inches MIN
.037 .002 .035 .012 .003 .110 .102 .059 .037 (TYP) .075 (TYP) .014 .024 (TYP) .010 (TYP) 0 8 .022
MAX
.057 .006 .051 .020 .008 .118 .118 .067
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NOTICE
Information furnished is believed to be accurate and reliable. However Globaltech Semiconductor assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties, which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Globaltech Semiconductor. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information without express written approval of Globaltech Semiconductor. (Revise Date:2007/11/13 Version_1.0)
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