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ST777/778/779
LOW VOLTAGE INPUT, 3-3.3V/5V/ADJUSTABLE OUTPUT DC-DC CONVERTER WITH SYNCHRONOUS RECTIFIER
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1V TO 6V INPUT GUARANTEES START-UP UNDER LOAD MAXIMUM OUTPUT CURRENT OF 300mA (778 OR 779 ADJUSTED TO 3V) LOAD FULLY DISCONNECTED IN SHUTDOWN TYPICAL EFFICIENCY OF 82% INTERNAL 1A POWER SWITCH AND SYNCHRONOUS RECTIFIER ADJUSTABLE CURRENT LIMIT ALLOWS LOW-COST INDUCTORS SUPPLY CURRENT OF 270A (NO LOAD) SHUTDOWN SUPPLY CURRENT 20A PACKAGE AVAILABLE: DIP-8 AND SO-8
DIP-8
SO-8
DESCRIPTION The ST777/778/779 are dc-dc converters that step-up from low voltage inputs requiring only three external components, an inductor (typically 22H) and two capacitors. The device include a Sinchronous Rectifier that eliminates the need for an external catch diode, and allows regulation even when the input is greater than the output. SCHEMATIC DIAGRAM
VIN
100F
Unlike others step-up DC-DC converters the ST777/778/779's Sinchronous Rectifier turns off in the shutdown mode, fully disconnecting the output from the source. This eliminates the current drain associated with conventional step-up converters when off or in shutdown. Supply current is 270A under no load and only 20A in stand by mode.
22H
RLIM
2
IN
DELAY TIMER
1
5
ILIM
LX
ACTIVE RECTIFIER
tOFF
SWITCH DRIVER
DELAY TIMER
OUT 6
VO
100F
tON
1:N
RECTIFIER CONTROL
PGND 4
SEL 8
VREF
1.25V
7 SHDN
SHUTDOWN CONTROL
AGND 3
October 2002
1/11
ST777/778/779
ABSOLUTE MAXIMUM RATINGS
Symbol VCC LX OUT, SHDN AGND to PGND FB PTOT TSTG TOP Parameter DC Input Voltage to GND Switch off Pin Voltage Switch on Pin Voltage Output, Shutdown Voltage Analog and Power Ground FB Pin Voltage Continuous Power Dissipation (at TA = 85C) DIP-8 Continuous Power Dissipation (at TA = 85C) SO-8 Storage Temperature Range Operating Ambient Temperature Range Value -0.3 to +7 -0.3 to +7 30 sec short to IN or OUT -0.3 to +7 -0.3 to +0.3 -0.3 to (OUT+0.3) 550 344 -40 to 150 0 to 85 Unit V V V V V mW C C
Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these condition is not implied.
ORDERING CODES
TYPE ST777 ST778 ST779 DIP-8 ST777ACN ST778ACN ST779ACN SO-8 ST777ACD ST778ACD ST779ACD
CONNECTION DIAGRAM
PIN CONNECTIONS
Pin No. 1 2 3 4 5 6 7 8 SYMBOL ILIM IN AGND PGND LX OUT SHDN NAME AND FUNCTION Sets switch current limit input. Connect to IN for 1A current limit. A resistor from ILIM to IN sets lower peak inductor currents. Input from battery Analog ground. Not internally connected to PGND. Power ground. Must be low impedance; solder directly to ground plane or star ground. Connect to AGND, close to the device. Collector of 1A NPN power switch and emitter of Sinchronous Rectifier PNP. Voltage Output. Connect filter capacitor close to pin. Shutdown input disables power supply when low. Also disconnets load from input. Threshold is set at VIN/2.
SEL/N.C./FB - Selection pin for 3/3.3V version (778); - Not internally connected for 5V version (777); - Feedback pin for adjustable version (779).
THERMAL DATA
Symbol Rthj-amb Parameter Thermal Resistance Junction-ambient DIP-8 100 SO-8 160 Unit C/W
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ST777/778/779
ELECTRICAL CHARACTERISTICS (VIN=2.5V, CI = 22F, CO=100F, SHDN and ILIM connected to IN, AGND connected to PGND, TA=0 to 85C, unless otherwise specified. Typical values are referred at TA=25C)
Symbol VSTART VIN(MAX) VO Parameter Start up Voltage Maximum Input Voltage Output Voltage ST777 779 (set to 5V), (Note 3) Output Voltage ST778 (Note 3) Test Conditions ILOAD < 10mA, TA = 25C (Note 1) (Note 1,2) ILOAD 30mA, VIN = 1.1V to 5V or ILOAD 80mA, VIN = 1.8V to 5V or ILOAD 130mA, VIN = 2.4V to 5V SEL=0V ILOAD 50mA,VIN =1.1V to 3.3V or ILOAD 210mA,VIN =1.8V to 3.3V or ILOAD 300mA,VIN =2.4V to 3.3V SEL=OPEN ILOAD 30mA, VIN =1.1V to 3V or ILOAD 210mA, VIN =1.8V to 3V or ILOAD 300mA, VIN =2.4V to 3V Output Voltage Range ST779 No Load Supply Current Shutdown Supply Current Shutdown Input Current Efficiency Shutdown Input Threshold Current Limit (Note 4) ILOAD = 0 mA, (Switch ON) (Note 5) SHDN=0V, (Switch OFF) SHDN = 0 to VIN SHDN = VIN to 5V VIH ILIM ILOAD=100mA VIN=1V to 6V 6 4.8 5.0 5.2 Min. Typ. Max. 1 Unit V V V
3.17
3.30
3.43
V
2.88
3.00
3.12
V
2.7 270 20 15 12 82 VIN/2 + 0.25 1.0 -0.3 1.2
6.5
V A
IIN ISHDN IIN SHDN
35 100 40
A nA A % V A %/C s
ILIM TEMPCO Current Limit Temperature Coefficient Minimum Switch Off Time tOFFMIN tONMAX Maximum Switch ON Time VIN=2.5V VIN=1.8V VIN=1V VCESAT NPN Switch saturation Voltage ISW=400mA ISW=600mA ISW=1000mA VCESAT NPN Rectifier Forward Drop ISW=400mA ISW=600mA ISW=1000mA VFB IFB ILX Error Comparator Trip Point ST779, over operating input voltage (Note 6) FB Pin Bias Current ST779, VFB=1.3V Switch Off Leakage Current Rectifier Off Leakage Current
4.5 6.5 15 0.25 0.33 0.5 0.18 0.22 0.4 1.232% 50 0.1 0.1 V nA A A V V
Note 1: Output in regulation, VOUT = VOUT (nominal) 4%. Note 2: At hight VIN to VOUT differentials, the maximum load current is limited by the maximum allowable power dissipation in the package. Note 3: Start-up guaranteed under these load conditions. Note 4: Minimum value is production tested. Maximum value is guaranteed by design and is not production tested. Note 5: In the ST779 supply current depends on the resistor divider used to set the output voltage. Note 6: VOUT is set to a target value of +5V by 0.1% external feedback resistors. VOUT is measured to be 5V2.5% to guarantee the error comparator trip point.
3/11
ST777/778/779
TYPICAL APPLICATION CIRCUIT
1 ILIM
SEL / N.C. / FB 8 R2
Vin 1/6V
2 V+
C1 22F
L1 22H
ST777 ST778 ST779
____
SHDN 7
R1
C3
3 AGND
Vout
6
C2 100F
Vo
4 PGND
LX
5
APPLICATIONS INFORMATION R1 and R2 must be placed only in ST779 applications to set the output voltage according to the following equation: VOUT = (1.23) [(R1+R2)/R2] and to simplify the resistor selection: R1 = R2 [(VOUT/1.23)-1] It is possible to use a wide range of values for R2 (10K to 50K) with no significant loss of accuracy thanks to the very low FB input current. To have 1% error, the current through R2 must be at least 100 times FB's bias current. When large values are used for the feedback resistors (R1>50K), stray output impedance at FB can incidentally add "lag" to the feedback response, destabilizing the regulator and creating a larger ripple at the output. Lead lengths and circuit board traces at the FB node should be kept short. Compensate the loop by adding a "lead" compensation capacitor (C3, 100pF to 1nF) in parallel with R1. The typical value of the L1 inductor is 22H, enough for most applications. However, are also suitable values ranging from 10F to 47F with a saturation rating equal to or greater than the peak switch -current limit. Efficiency will be reduced if the inductor works near its saturation limit, while will be maximized using an inductor with a low DC resistance, preferably under 0.2. Connecting ILIM to VIN the maximum LX current limit (1A) is set. If this maximum value is not required is possible to reduce it connecting a resistor between ILIM and VIN (See Figure 16 to choose the right value). The current limit value is misured when the switch current through the inductor begins to flatten and does'nt coincide with the max short circuit current. Even if the device is designed to tolerate a short circuit without any damage, it is strictly recommended to avoid a continuos and durable short circuit of the output to GND. To achieve the best performances from switching power supply topology, particular care to layout drawing is needed, in order to minimize EMI and obtain low noise. Moreover, jitter free operation ensures the full device functionality. Wire lengths must be minimized, filter and by-pass capacitors must be low ESR type, placed as close as possible to the integrated circuit. Solder AGND and PGND pins directly to a ground plane.
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ST777/778/779
TYPICAL CHARACTERISTICS (unless otherwise specified Tj = 25C, CI=22F, CO=100F) Figure 1 : Output Voltage vs Temperature Figure 4 : Efficiency vs Input Voltage
Figure 2 : Output Voltage vs Temperature
Figure 5 : Efficiency vs Output Current
Figure 3 : Efficiency vs Temperature
Figure 6 : Efficiency vs Low Output Current
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ST777/778/779
Figure 7 : No Load Supply Current vs Input Voltage Figure 10 : Minimum Switch Off Time vs Temperature
Figure 8 : No Load Supply Current vs Temperature
Figure 11 : Maximum Switch ON Time vs Temperature
Figure 9 : Shutdown Input Threshold vs Input Voltage
Figure 12 : FB Pin Bias Current vs Temperature
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ST777/778/779
Figure 13 : Error Comparator Trip Point vs Temperature Figure 15 : Maximum Output Current vs Input Voltage
Figure 14 : Maximum Output Current vs Input Voltage
Figure 16 : Peak Inductor Current vs Current-Limit Resistor
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ST777/778/779
Figure 17 : Line Transient Figure 19 : Switching Waveform
Vin
Vout
Vout
Isw
Vin=1.1V Iout=30mA
Figure 18 : Load Transient
Figure 20 : Switching Waveform
ST777/779
Vout (5V)
Vout
Iout
Vin=2.5V Iout=10mA to 130mA
Isw
Vin=2.5V Iout=30mA
PRINTED DEMOBOARD (Not in scale)
8/11
ST777/778/779
Plastic DIP-8 MECHANICAL DATA
mm. DIM. MIN. A a1 B B1 b b1 D E e e3 e4 F I L Z 0.44 3.3 1.6 0.017 8.8 2.54 7.62 7.62 7.1 4.8 0.130 0.063 0.38 0.7 1.39 0.91 0.5 0.5 9.8 0.346 0.100 0.300 0.300 0.280 0.189 0.015 1.65 1.04 TYP 3.3 0.028 0.055 0.036 0.020 0.020 0.386 0.065 0.041 MAX. MIN. TYP. 0.130 MAX. inch
P001F
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ST777/778/779
SO-8 MECHANICAL DATA
DIM. A a1 a2 a3 b b1 C c1 D E e e3 F L M S 3.8 0.4 4.8 5.8 1.27 3.81 4.0 1.27 0.6 8 (max.) 0.149 0.015 5.0 6.2 0.65 0.35 0.19 0.25 0.1 mm. MIN. TYP MAX. 1.75 0.25 1.65 0.85 0.48 0.25 0.5 45 (typ.) 0.189 0.228 0.050 0.150 0.157 0.050 0.023 0.196 0.244 0.025 0.013 0.007 0.010 0.003 MIN. inch TYP. MAX. 0.068 0.009 0.064 0.033 0.018 0.010 0.019
0016023
10/11
ST777/778/779
Information furnished is believed to be accurate and reliable. However, STMicroelectronics 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 STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. (c) The ST logo is a registered trademark of STMicroelectronics (c) 2002 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - United States. (c) http://www.st.com
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