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SS6578
High-Efficiency, Step-Down DC/DC Controller
FEATURES
4V to 18V input voltage operation. High-efficiency (up to 95%). Low quiescent current at 90A. Pulse-skipping and pulse-frequency modulation. Inputs-uncommitted current-sense comparator. Duty-cycle adjustable. 90KHz to 280KHz oscillator frequency. Power-saving shutdown mode (8A typical). Push-pull driver output.
DESCRIPTION
The SS6578 is a high performance step-down DC/DC controller, designed to drive an external P-channel MOSFET to generate programmable output voltages. Two main schemes of Pulse-Skipping and Pulse-Frequency Modulation are employed to maintain low quiescent current and high conversion efficiency under wide ranges of input voltage and loading condition. The SS6578 delivers 10mA to 2A of output current with 87%~93% efficiency at
APPLICATIONS
* Notebook 5V/3.3V Main Power * Step-Down DC/DC Controller Modules. * Constant-Current Source for Battery Chargers.
VIN=9V, VOUT=5V condition. A current-sense comparator with both inverting and non-inverting inputs uncommitted is included to provide the crucial function of either current-limit protection or constant-output current control. When the SS6578 is used in a high-side current-sensing step-down constant-current source, the efficiency is typically greater than 90%. Duty-cycle can be adjusted to greater than 90% by connecting a resistor from DUTY pin to VIN. Quiescent current is about 90A and can be reduced to 8A in shutdown mode. The switching frequency range of around 90 kHz to 280 kHz allows small size switching components, which are ideal for battery powered portable equipment.
ORDERING INFORMATION
SS6578CXXX
Packing TR: Tape and reel TB: Tubes Packaging S: SO-8 N: PDIP-8
PIN CONFIGURATION
SO-8
VIN DUTY SHDN FB
TOP VIEW
1 2 3 4 8 CS+ 7 CS6 DRI 5 GND
Example: SS6578CSTR a in SO-8 package, shipped in tape and reel packing (PDIP-8 is only available in tubes)
Rev.2.02 4/06/2004
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SS6578
TYPICAL APPLICATION CIRCUIT
+VIN 6.4~18V +VOUT, 5V * Rs L1 33H + R3 12K R4 3K9
Q1 D1 GS SS32
C4 470F
1 R6 + C1 100F C2 0.1F 1M <15V 2 3 4
VIN DUTY SHDN FB
CS+ CSDRI GND
8 7 6 5 R7 **
U1 SS6578
IP = IO,MAX +
RS =
VO( VIN - VO ) 2VIN x f S x L
VTH 50mV 0.1VIN fS L = = IP IP 2VIN f S LIO,MAX + VIN VO - VO 2 VIN: Input voltage VOUT: Output voltage fS: Working frequency L= Inductor value IO,MAX: Maximum Output current VTH: Current Limit Sense Threshold **VIN>15V, R7=15 VIN15V, R7=0
DC/DC Buck Converter
ABSOLUTE MAXIMUM RATINGS
VIN Supply Voltage..................................................................................................... 20V DUTY Voltage............................................................................................................ 20V
SHDN Voltage............................................................................................................ 15V
Operating Temperature Range........................................................................... 0C~70C Storage Temperature Range....................................................................... -65C~ 150C
TEST CIRCUIT
Refer to TYPICAL APPLICATION CIRCUIT.
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SS6578
ELECTRICAL CHARACTERISTICS
(VIN= 13V, TA=25C, unless otherwise specified.)
PARAMETERS Operation Voltage Quiescent Current Shutdown Mode Current Internal Reference Voltage Driver Sinking "ON Resistance" Driver Sourcing "ON Resistance" Current Limit Sense Threshold Shutdown Threshold VCS+ = 13V 50 0.8 V SHDN < 15V VDUTY = VIN VDUTY = VIN 71 225 VFB = 1.5V V SHDN = 0V 1.16 CONDITIONS MIN. 4 90 8 1.22 16 11 70 1.5 90 2.4 1 TYP. MAX. 20 160 20 1.28 UNIT V A A V mV V A % KHz
SHDN Pin Leakage Current
Duty Cycle Oscillator Frequency
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SS6578
TYPICAL PERFORMANCE CHARACTERISTICS
90 35
90
TA = 27C
85 80
Duty Frequency
30 0 25 20 15 10 50 0 20
85
Frequency (KHz)
VIN=5V Duty Cycle (%)
80
Duty (%)
75 70 65 60 55 4 6 8 10 12 14 16 18
75
VIN=13V
70
65
VIN=20V
60 0 20 40 60 80
Fig. 1
VIN ( V) Frequency & Duty Cycle vs. VIN
Temperature (C) Fig. 2 Duty Cycle vs.Temperature
10
290
VIN=5V
VIN=20V
90
Frequency (KHz)
240
Duty Cycle (%)
190
VIN=13V
80
VIN=10V VIN=15V
140
VIN=5V
70
VIN=20V RDUTY refer to Typ. App.
Circuit.
1 2 3 4
90 0
10
20
30
40
50
60
70
60 0
Temperature (C) Fig. 3 Frequency vs. Temperature
RDUTY (M) Fig. 4 Duty Cycle vs. RDUTY
20
110
Shutdown Current (A)
15
TA=25C TA=0C
10
Quiescent Current (A)
100
TA= 0C
90
TA= 25C
80
T A= 70C
5
TA=70C
70
0 4 6 8 10 12 14 16 18 20
60
4
6
8
10
12
14
16
18
20
VIN (V) Fig. 5 Shutdown Current vs. VIN
Fig. 6
VIN (V) Quiescent Current vs. VIN
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SS6578
BLOCK DIAGRAM
Current Limit Comparator VIN 1 + 70mV 8 CS+
DUTY 2 PFM OSC VIN LATCH 7 CS-
SHDN
3
+ Error Comparator 1.22V Reference Voltage Output Driver
6
DRI
FB
4
5
GND
PIN DESCRIPTIONS
PIN 1: VIN - Input supply voltage - a range of 4V to 18V is recommended. Connecting a resistor R1 to converter output node and a resistor R2 to ground yields the output voltage: VOUT=1.22 x (R1+R2)/ R2 PIN 5: GND - Power ground. PIN 6: DRI - Push-pull driver output to drive an external P-channel MOSFET or PNP transistor. When driving a PNP bipolar transistor, a base resistor and a capacitor to the base of PNP are recommended. - Current-sense comparator inverting input. This pin voltage should go over 2V but should not exceed VIN voltage.
PIN 2: DUTY - Duty cycle adjustment pin. To be tied to the VIN pin directly or through a resistor R DUTY to adjust oscillator duty cycle. RDUTY must be over 1M if VIN=20V. See TYPICAL PERFORMANCE CHARACTERISTICS. PIN 3: SHDN- Logical input to shutdown the chip: VSHDN = High for normal operation. VSHDN = Low for shutdown. This pin should not be floating or be forced to over 15V. In shutdown mode DRI pin is held high. PIN 4: FB - Feedback comparator input, to compare the feedback voltage with the internal reference voltage.
PIN 7: CS-
PIN 8: CS+ - Current sense comparator non-inverting input. This pin voltage should go over 2V but should not exceed VIN voltage.
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SS6578
APPLICATION EXAMPLES
Efficiency vs. Load Current
0.1F C2 100F VIN + C1 6.4 ~ 18V
100
VOUT=5V
95
VIN DUTY 5V SHDN FB SS6578 R2 15.4K VIN>15V, R7=15 VIN15V, R7=0
CS+ RS *R7 Q1 33H *L1 GS SS32 D1 R1 47K *:Sumida MPP Core
80 10
100 1000
DRI GND
VOUT 5V/2A +
Efficiency (%)
CS-
90
VIN=6.4 V
VIN=9V
330F C3
85
VIN=16 V
Load Current (mA)
Fig. 7 5V Step-Down Converter
VIN C1 12 ~ 18V
95
100F
0.1F
C2
+
Efficiency vs. Load Current VOUT=3.3V
VIN DUTY 5V SHDN FB
CS+ CSDRI GND SS6578
RS R1** 680 R7 6.8V D2 GS SS32 D1 R1 47K *:Sumida MPP Core Q1 33H *L1 330F C3 + VOUT
90
Efficiency (%)
3.3V/2A
85
R2 27.4K VIN>15V, R7=15 VIN15V, R7=0
80
VIN=16V
75 10 10 1000
**R1 value is based on the current rating of D2
Load Current (mA)
Fig. 8 3.3V Step-Down Converter
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SS6578
APPLICATION EXAMPLES
VIN 5~8V R4 1K Q1 D1 SS32
(Continued)
1N4148 33H *L1 U1 VIN C3 *RS + C4 10F D2
D3 + 330F 35V
SS32
CS+ CSDRI GND
C1 100F
+
C2 0.1F
R6 RDUTY DUTY R1 1M FB 1M SHDN
R7 ** SS6578
VBATT R3 R2 20/5W LED1 R8 240K + R9 100K C9 4.7F C7 0.1F R10 100K YELLOW 1 PEAK 2 C10 47nF Q3
9014
SW1 LED2 PB SW R12 100K DSW ICON LED2 LED1 GND SEL1 SEL2 MODE 16 15 14 13 12 11 10 9 R16 680 R17 680 GREEN RED LED3
510
U2
R15 680
VBT 3 DIS 4 VTS 5 VCC
BAT1 RX BATTERY
THERMISTOR
6 R14 + C11 200K C8 7 8 R11 240K
ADJ SEL3 TMR
100K RY 100K C6 0.1F
100F R13 470K
0.1F
SS6781
Q2 MMBT2222A
U3 78L05
+
*:Sumida MPP Core
VIN C12 1F GND
VOUT
+ C13
10F
VIN>15V, R7=15 VIN15V, R7=0
NOTE:
RS =0.1, charge current =0.5A 10%, VIN>VBATT +3.5V RS =0.05, charge current =1A10%, VIN>VBATT +4V RS =0.033, charge current =1.5A 10%, VIN>VBATT +4.5V Efficiency>90%, measured at CS- node 3~5 NiMH/NiCd Cells
Fig. 9 Battery Charger Circuit with High-Side Current-Sensing Constant Current Source
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SS6578
APPLICATION INFORMATION
A. Start Up Design In order to eliminate the over-shoot issue which happens when Vout is under 5V, we offer two solutions for the SS6578 as a buck controller. 1. Buck Converter with 12V12V< +V IN <15V Rs Q1 SSM4435 D1 SS32 L1 33H
+VOUT, 3.3V
R1 680
1 2
VIN DUTY SHDN FB
CS+ CSDRI GND
8 7 6 5
+ C4 330F R2 47K R3 27K
+ C1 100 C2 0.1F D2 6.8V
3 4
U1 SS6578
Fig. 10 DC/DC Buck Converter VOUT=3.3V
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SS6578
+VIN = 5~18V Rs R2 100K Q1 SSM4435 D1 SS32 L1 33H C4 470F
+VOUT, 3.3V + R3 47K R4 27K
+ C1 100F
1 VIN D2 LL4148
*** R6
Q2 R1 3K3 1M C2 <15V 0.1uF
CS+ 8 CS- 7 DRI GND 6 5 R7 *
2 DUTY 3 SHDN 4 FB
C3 1F
U1 SS6578
*
VIN>15V, R7=15 VIN15V, R7=0*
*** R6 can adjust the duty cycle max. It can be 0 Fig 11. DC/DC Buck Converter VOUT =3.3V
B. Short Circuit Protection Design 1. As we know, Short Circuit
Protection
A fuse can be selected to pass the start up current, but open quickly with a large unexpected current. Of course, replacement of the fuse is needed after short circuit. 3. Design 2: shown as Fig. 13. Method: Add a SCP circuit Note: 1. The time constant, which is directly related to R1 and C1, has a serious effect on the circuit. 2. Circuit can be recovered by removing the short circuit event from the system. 3. The condition for applying this design is VOUT 3V.
(abbreviated as SCP) does not always exist in the DC-DC converter circuit. The fact is usually the DC-DC converter provides the circuits attached to VOUT with low power or low voltage. Sometimes there is less concern about safety, as the probability of short-circuit is quite low. That gives users reasons to ignore the use of an SCP circuit. However, we would still like to point out the importance of the protection. With SCP, the system will be well protected in any situation. Two SCP circuits are introduced as follows for your reference. 2. Design1: shown as Fig. 12. Method: Add a fast fuse to VOUT.
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SS6578
+VIN 12V
Rs 20mR Q2 R6 680 1 VIN CS+ CSDRI GND 8 7 C4 6 1500F/6.3V 5 + L2 D2 SS32 33H
FUSE1 +VOUT, 5V/2A Fast 3A
+ C5 470/16V
2 DUTY C2 0.1F D3 6.8V 3 SHDN
R8 12K R9 3K9
4 FB
U2 SS6578
Fig 12. Add a Fast Fuse Solution
+VIN 12V R1 240K C1 1 Rs R2 10K Q1 PNP mmbt3906 20mR Q2 R6 680 1 VIN 2 DUTY 3 SHDN 4 FB CS+ 8 CS- 7 DRI GND 6 1500F 6.3V 5 R8 12K R9 3K9 L2 33H D2 SS32 +VOUT, 5V/2A
+ 470F C5 16V C2 0.1F
D3 6.8V
C4 +
U2 SS6578
LL4148
D1
Short Circuit Protection
Fig 13. Add A Short Circuit Protection Circuit Solution
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SS6578
PHYSICAL DIMENSIONS
8 LEAD PLASTIC SO (unit: mm)
D
SYMBOL A
H E
MIN 1.35 0.10 0.33 0.19 4.80 3.80
MAX 1.75 0.25 0.51 0.25 5.00 4.00 1.27(TYP)
A1 B C D
e A C A1
E e H L
L
5.80 0.40
6.20 1.27
B
8 LEAD PLASTIC DIP (unit: mm)
D
SYMBOL A1
E1
MIN 0.381 2.92 0.35 0.20 9.01 7.62 6.09 -- 2.92
MAX -- 4.96 0.56 0.36 10.16 8.26 7.12 10.92 3.81
A2 b
E
C D
A2 A1
L
E
C eB
E1 e eB L
2.54 (TYP)
b
e
Information furnished by Silicon Standard Corporation is believed to be accurate and reliable. However, Silicon Standard Corporation makes no guarantee or warranty, express or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infringement of any patent or other intellectual property rights of third parties that may result from its use. Silicon Standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. No license is granted, whether expressly or by implication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of Silicon Standard Corporation or any third parties.
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