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SS6845G
Regulated 5V Charge Pump
PRODUCT SUMMARY
Input voltage range: 2.7V to 5.0V Regulated output voltage of 5V 4% Output current: 100mA (VIN = 3.3V) 110mA (VIN = 3.6V)
DESCRIPTION
The SS6845G is a micropower charge pump DC/DC converter that produces a regulated 5V output. The input voltage range is 2.7V to 5.0V. Extremely low operating current (13A typical with no load) and a low external part count (one 0.22F flying capacitor and two small bypass capacitors at the input and output) make the SS6845G ideally suitable for small, batterypowered applications. The SS6845G operates as a PSM-mode (Pulse Skipping Modulation) switched capacitor voltage doubler to produce a regulated output and features thermal shutdown capability and short circuit protection.
FEATURES
Ultralow power: I IN = 13A No inductors needed Very low shutdown current: <1A Internal oscillator: 650KHz Short-circuit and over-temperature protection
APPLICATIONS
White or Blue LED Backlighting SIM Interface Supplies for Cellular Telephones Li-Ion Battery Backup Supplies Local 3V to 5V Conversion Smart Card Readers PCMCIA Local 5V Supplies
Pb-free; RoHS-compliant SOT-23-6 package
TYPICAL APPLICATION CIRCUIT
VOUT
** R1
U1 1-Cell Li-ion Battery CIN 2.2F 1 VOUT 2 3 SHDN SS6845G CGND C+ 6 VIN 5 4 0.22F CFLY COUT 2.2F
*
*
*
*
Regulated 5V Output from 2.7V to 5.0V Input * ** WLED series number: NSPW310BS, VF=3.6V, IF=20mA
R1 = VOUT - VF , where NWLED is the number of WLEDs. IF x N WLED
CIN, COUT: CELMK212BJ225MG (X5R) (0805), TAIYO YUDEN CFLY : CEEMK212BJ224KG (X7R) (0805), TAIYO YUDEN
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SS6845G
ORDERING INFORMATION
SS6845GG TR Packing type: TR: Tape and reel Package type: GG: RoHS-compliant SOT-23-6
SOT-23-6 TOP VIEW
C+ VIN 6 5 C4
PIN CONFIGURATION
(MARK SIDE) 1 2 3
VOUT GND SHDN
SOT-23-6 Marking
Part No. SS6845GG Marking BO50P
ABSOLUTE MAXIMUM RATINGS
VIN to GND VOUT to GND All other ins to GND VOUT short-circuit duration Operating ambient temperature range Junction temperature Storage temperature range Lead temperature (minimum 10 seconds) 6V 6V 6V Continuous -40C to 85 C 125C -65C to 150 C 260C
Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
TEST CIRCUIT
Refer to the TYPICAL APPLICATION CIRCUIT on page 1.
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SS6845G
ELECTRICAL CHARACTERISTICS
(TA=25C, CFLY=0.22F, CIN=2.2F, COUT=2.2F, unless otherwise specified.) (Note 1)
PARAMETER Input voltage 2.7V VIN< 3.3V, IOUT 30mA 3.3V VIN 5.0V, IOUT 60mA VIN=3V, VOUT=5.0V SHDN =VIN 2.7V VIN 5.0V, IOUT=0 , SHDN =VIN 2.7V VIN 5.0V, IOUT=0 , SHDN =0V VIN =3V, IOUT=50mA VIN =2.7V , IOUT=30mA Oscillator free-running TEST CONDITIONS SYMBOL VIN MIN. 2.7 4.8 VOUT 4.8 5.0 5.2 mA 13 0.01 60 83 650 1.4 0.3 -1 -1 0.5 170 1 1 30 1.0 A A mV % KHz V V A A mS mA 5.0 TYP. MAX. 5.0 5.2 V UNIT V
Output voltage
Continuous output current Supply current Shutdown current Output ripple Efficiency Switching frequency Shutdown input threshold (High) Shutdown input threshold (Low) Shutdown input current (High) Shutdown input current (Low) Vout turn-on time Output short-circuit current
IOUT
ICC I SHDN VR fOSC VIH VIL
60
SHDN =VIN SHDN = 0V
IIH IIL tON ISC
VIN =3V, IOUT = 0mA VIN=3V, VOUT= 0V, SHDN = VIN
Note1: Specifications are production tested at TA=25C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC).
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SS6845G
TYPICAL PERFORMANCE CHARACTERISTICS
(CN, COUT: CELMK212BJ225MG, CFLY: CEEMK212BJ224KG)
5.15 5.10 IOUT=25mA
20
Supply Current ()
Output Voltage (V)
5.05 5.00 4.95 4.90 4.85 2.5
COUT=10F CFLY=1F TA = -40C TA =25C TA =85C
TA=-40C
15
TA=25C
10
TA=85C
IOUT=0A CFLY=1F VSHDN=VIN
5 2.5 3.0 3.5 4.0 4.5 5.0
3.0
3.5
4.0
4.5
5.0
Supply Voltage (V) Fig. 1 Line Regulation
5.15 5.10 TA=25C COUT=10F CFLY=1F VIN=3.6V
Supply Voltage (V) Fig. 2 No Load Supply Current vs. Supply Voltage
5.2 5.1
Output Voltage (V)
Output Voltage (V)
5.05 5.00 4.95 4.90 VIN=2.7V 4.85 0 20 40 VIN=3.0V 60 80 100 VIN=3.3V
5.0 4.9 4.8 4.7 4.6 4.5
VIN=3.3V VIN=3.6V TA=25C CFLY=0.22F COUT=2.2F
0 10 20 30 40
VIN=2.7V
50 60 70 80
VIN=3.0V
90 100 110 120 130
120
140
160
Output Current (mA) Fig. 3 Load Regulation
100 90 80
100
Output Current (mA) Fig. 4 Load Regulation
CT=25C CFLY=1F
VIN=2.7V
90 80 70 60 50 40 30 0.01
VIN=2.7V
VIN=3.0V
Efficiency (%)
60
50 40 30 20 10
VIN=3.0V VIN=3.3V VIN=3.6V
Efficiency (%)
70
VIN=3.3V
VIN=3.6V
TA=25C CFLY=0.22F
0.1 1 10 100
0
0.001
0.01
0.1
1
10
100
Output Current (mA) Fig. 5 Efficiency
Output Current (mA) Fig. 6 Efficiency
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SS6845G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
50 45 40 175 150
Output Ripple (mV)
Output Ripple (mV)
35 30 25 20 15 10
125
VIN=3.6V
VIN=3.6V
100 75
VIN=3.3V VIN=3.0V VIN=2.7V 0 20
40 60 80
VIN=3.3V
50 25
COUT=10F CFLY=1F
100 120 140
VIN=3.0V VIN=2.7V
0 20 40 60 80
COUT=2.2F CFLY=0.22F
100 120 140
5
0
0
Output Current (mA) Fig.7 Output Current vs. Output Ripple
Output Current (mA)
Fig. 8 Output Current vs. Output Ripple
1000
5.05
900
VIN=2.5V
800
Output Voltage (V)
Frequency (KHz)
5.00
700
4.95
VIN=3.0V CFLY=1F IOUT=50mA
600
4.90
500
400
-60
-40
-20
0
20
40
60
80
100
120
140
Temperature (C) Fig. 9 Frequency vs. Temperature
280
4.85 -60
-40
-20
0
20
40
60
80
100
120
140
Fig. 10
Temperature (C) Output Voltage vs. Temperature
Short-Circuit Current (mA)
Short-Circuit Current (mA)
260 240 220 200 180 160 140 120 100 2.5
TA=25C CFLY=1F
220 200 180 160 140 120 100
TA=25C CFLY=0.22F
2.5 3.0 3.5 4.0 4.5 5.0 5.5
3.0
3.5
4.0
4.5
5.0
Supply Voltage (V) Fig. 11 Short-Circuit Current vs. Supply Voltage
Supply Voltage (V) Fig. 12 Short-Circuit Current vs. Supply Voltage
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SS6845G
TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
CN
CN
VOUT VOUT
Fig. 13
Output Ripple
VIN=3.0V, IOUT=50mA, COUT=10F,CFLY=1F
Fig. 14 Output Ripple VIN=3.0V, IOUT=50mA, COUT=2.2F, CFLY=0.22F
IOUT
VOUT
VOUT
IOUT
Fig. 15 Load Transient Response VIN=3.0V, IOUT=0mA~50mA,COUT=10F, CFLY=1F
Fig. 16 Load Transient Response VIN=3.0V, IOUT=0mA~50mA,COUT=2.2F, CFY=0.22F
VOUT
VOUT
V SHDN
V SHDN
Fig. 17 Start-Up Time VIN=3.0V, IOUT=0A, COUT=10F
Fig. 18 Start-Up Time VIN=3.0V, IOUT=0A, COUT=2.2F
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SS6845G
BLOCK DIAGRAM
VOUT 2 COUT 2.2F 1 VIN Control COMP CVREF SHDN 1 2 CFLY
0.22F
C+
CIN 2.2F
PIN DESCRIPTIONS
PIN 1:VOUT Regulated output voltage. For the best performance, VOUT should be bypassed with a 2.2F (min) low ESR capacitor with the shortest possible leads. Ground. Should be tied to a ground plane for best performance. PIN 4: CPIN 5: VIN Flying capacitor negative terminal. Input supply voltage. VIN should be bypassed with a 2.2F (min) low ESR capacitor. Flying capacitor positive terminal.
PIN 2: GND -
PIN 6: C+
-
PIN 3: SHDN - Active-low shutdown input. A low voltage on SHDN disables the SS6845G. SHDN is not allowed to float.
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SS6845G
APPLICATION INFORMATION
Introduction
The SS6845G is a micropower charge pump DC/DC converter that produces a regulated 5V output with an input voltage range from 2.7V to 5.0V. It utilizes the charge pump topology to boost VIN to a regulated output voltage. Regulation is obtained by sensing the output voltage through an internal resistor divider. A switched doubling circuit enables the charge pump when the feedback voltage is lower than the trip point of the internal comparator, and vice versa. When the charge pump is enabled, a two-phase non-overlapping clock activates the charge pump switches. To maximize battery life for a battery-use application, quiescent current is limited to no more than 13A.
Short Circuit/Thermal Protection
The SS6845G includes built-in short circuit current limiting as well as over-temperature protection. During a short circuit condition, the output current is automatically constrained to approximately 170mA. This short circuit current will cause a rise in the internal IC junction temperature. When the die temperature exceeds 150C, the thermal protection will shut down the charge pump switching operation and the die temperature will then reduce. Once the die temperature drops below 135C, the charge pump switching circuit will restart. If the fault has not been eliminated, the this protection mechanism will repeat again and again, allowing the SS6845G to work continuously in a short circuit condition without damaging the device.
Operation
This kind of converter uses capacitors to store and transfer energy. Since the capacitors can't change their voltage level abruptly, the voltage ratio of VOUT over VIN is limited to some range. Capacitive voltage conversion is obtained by switching a capacitor periodically. It first charges the capacitor by connecting it across a voltage source and then connects it to the output. Referring to Fig. 19, during the on state of internal clock, Q1 and Q4 are closed, which charges C1 to VIN level. During the off state, Q3 and Q2 are closed. The output voltage is VIN plus VC1, that is, 2VIN.
VIN CIN Q3 Q1 C1 Q4 Q2 VOUT COUT
Shutdown
In shutdown mode, the output is disconnected from the input. The input current is extremely low since most of the circuitry is turned off. Due to high impedance, the shutdown pin cannot float.
Efficiency
The diagrams, Fig. 20 and Fig. 21 show the operation of the charge pump in the on and off states. R DS-ON is the resistance of the switching element during conduction. ESR is the equivalent series resistance of the flying capacitor C1. ION-AVE and IOFF-AVE are the average current during the on-state and off-state, respectively. D is the duty-cycle, which means the ratio of the on-state time to the total cycle time. Let's look at capacitor C1 - assuming that capacitor C 1, has reached its steady state, then the amount of charge flowing into C 1 during the on-state is equal to that flowing out of C 1 during the off-state.
Fig. 19 The circuit of charge pump
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SS6845G
ION- AVE x DT = IOFF - AVE x (1 - D)T ION- AVE x D = IOFF - AVE x (1 - D)
(1) (2)
External Capacitor Selection
Three external capacitors, CIN, COUT and CFLY, determine SS6845G performance, in the area of output ripple voltage, charge pump strength and transients. Optimum performance can be obtained by the use of ceramic capacitors with low ESR. Due to their high ESR, tantalum and aluminum capacitors are not recommended for charge-pump applications. To reduce noise and ripple, a low ESR ceramic capacitor, ranging from 2.2F to 10F, is recommended for CIN and COUT. The value of COUT determines the amount of output ripple voltage. An output capacitor with a larger value results in smaller ripple. CFLY is critical to the performance of a charge pump. The larger CFLY is, the larger the output current and the smaller the resulting ripple voltage. However,
a large CFLY requires large CIN and COUT.
IIN = ION- AVE x D + IOFF- AVE x (1 - D) = 2 x ION- AVE x D = 2 x IOFF- AVE x (1 - D) IOUT = IOFF- AVE x (1 - D) IIN = 2IOUT
(3)
..........(4)
For the SS6845G, the controller uses the PSM (Pulse Skipping Modulation) control strategy. When the duty cycle is limited to 0.5, then:
ION- AVE x 0.5 x T = IOFF- AVE x (1 - 0.5) x T ION- AVE = IOFF- AVE
..........(5)
According to the equation (4), we know that as long as the flying capacitor C1 is at steady state, the input current is twice the output current. The efficiency of charge pump is given below:
=
VIN
CIN
VOUT x IOUT V xI V = OUT OUT = OUT ..(6) VIN x IIN VIN x 2IOUT 2VIN
Q1 RDS-ON Q3 ESR C1 Q4 Q2 VOUT COUT
ION
The ratio of CIN (as well as COUT) to CFLY should be approximately 10:1. The values of the capacitors used under operating conditions, determine the performance of the charge pump converter, and two factors, described below, affect the value of the capacitors. 1. Material: Ceramic capacitors of different materials, such as X7R, X5R, Z5U and Y5V, have different tolerances to temperature and capacitance can vary significantly. For example, X7R or X5R types of capacitor retain their capacitance over temperatures from -40C to 85C, but a Z5U or Y5V type will change a lot over that temperature range.
RDS-ON
Fig. 20 The on-state of charge pump circuit
VIN CIN
RDS-ON Q1 Q3 RDS-ON
IOFF
Q2
VOUT COUT
ESR Q4 C1
Fig. 21 The off-state of charge pump circuit
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SS6845G
2. Package Size: A ceramic capacitor with large volume (0805), gets a lower ESR than a small one (0603). Therefore, larger devices provide improved transient response over smaller ones. Table 1 lists the recommended components for use with the SS6845G. Table.1 Bill of Material
Designator Part Type Description Vendor
2 PESR IOUT x ESR x 2 = IOUT x 4ESR
With a duty-cycle of 0.5, the power loss of RDS-ON is
2 PRDS -ON IOUT x
2 x RDS - ON 0.5(1 - 0.5)
2 = IOUT x 8R DS - ON
1 0.5(1 - 0.5)
In fact, whether the current is the on-state or the off-state, it decays exponentially rather than flows steadily, and as the root mean square value of exponential decay is not equal to that of steady flow, then we must use an approximation. Let's use another approach to look at the charge pump circuit and focus on the flying capacitor C1. Referring to Fig. 20, when the circuit is in the on state, the voltage across C1 is:
VC-ON (t) = VIN - 2R DS-ON x ION (t) - ESR x ION (t) ...(9)
CIN
2.2
CELMK212BJ225MG (X5R) CEEMK212BJ -224KG (X7R) CELMK212BJ225MG (X5R)
TAIYO YUDEN TAIYO YUDEN TAIYO YUDEN
CFLY
0.22
COUT
2.2
Power Dissipation
Now, let's look at the power dissipation in R DS-ON and ESR. Assume that the RDS-ON of each internal switching element in the SS6845G is equal and ESR is the equivalent series resistance of CFLY (refer to Fig. 20 and Fig. 21). The approximation of the power losses of R DS-ON and ESR are given below:
PRDS-ON
2 ION- AVE 2 x 2RDS - ON x D + IOFF - AVE
The average of VC1 during the on-state is:
VC-ON- AVE = VIN - 2R DS-ON x ION- AVE - ESR x ION- AVE ............................(10)
Similarly, referring to Fig. 21, when the circuit is in the off-state, the voltage of C1 is:
VC-OFF (t) = VOUT - VIN + 2R DS-ON x IOFF (t) + ESR x IOFF (t) .................................(11)
x 2RDS - ON x (1 - D)
IIN 2 I ) x 2RDS - ON x D + ( OUT )2 x 2RDS - ON x (1 - D) 2D 1- D 2IOUT 2 I =( ) x 2RDS -ON x D + ( OUT )2 x 2RDS -ON x (1 - D) 2D 1- D 2 2 2 2 = IOUT x ( RDS - ON ) + IOUT x ( RDS -ON ) D 1- D 2 2 = IOUT x x RDS -ON D(1 - D) =(
The average of VC1 during the off-state is:
VC-OFF- AVE = VOUT - VIN + 2R DS-ON x IOFF- AVE + ESR x IOFF- AVE ....................(12)
..........(7)
2 2 PESR ION- AVE x ESR x D + IOFF- AVE x ESR x (1 - D)
I IIN 2 ) x ESR x D + ( OUT ) 2 x ESR x (1 - D) 2D 1- D 12 1 2 = IOUT x ESR x + IOUT x ESR x D 1- D 1 2 = IOUT x ESR x D(1 - D) =(
The difference in charge stored in C 1 between the on-state and off-state is the net charge transferred to the output in one cycle.
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SS6845G
Q = Q ON - Q OFF = C1 x (VC1-ON- AVE - VC1-OFF - AVE ) = C1 x (2VIN - VOUT - 2R DS-ON x ION- AVE - 2R DS-ON x IOFF- AVE - ESR x ION- AVE - ESR x IOFF- AVE ) = C1 x (2VIN - VOUT - 2R DS -ON x = C1 x [2VIN - VOUT - (2R DS-ON I I I IOUT - 2R DS -ON x OUT - ESR x OUT - ESR x OUT ) 1- D D 1- D D 1 + ESR) x IOUT x ] D(1 - D)
.........(13)
Thus the output current can be written as
IOUT = f x Q = f x (Q ON - Q OFF ) = f x C1 x [2VIN - VOUT - (2R DS-ON + ESR ) x IOUT x 1 ] D(1 - D)
(14)
When the duty cycle is 0.5, the output current can be written as:
IOUT = f x C1 x [2VIN - VOUT - (2R DS-ON + ESR) x IOUT x = fC1 x [2VIN - VOUT - (8R DS-ON + 4ESR) x IOUT ] 1 ] 0.5(1 - 0.5)
(15)
And equation (15) can be re-written as:
2VIN - VOUT = 1 x IOUT + (8R DS-ON + 4ESR) x IOUT fC1
(16)
According to equation (16), when the duty cycle is 0.5, the equivalent circuit of the charge pump is shown in Fig. 22. The term 8RDS-ON is the total effect of switching resistance, 1/fC1 is the effect of flying capacitor and 4ESR is its equivalent resistance. From the equivalent circuit shown in Fig. 22, it is seen that the terms 1/fC1, 4ESR and 8RDS-ON should be as small as possible to get large output current. However, since the R DS-ON is internal to the SS6845G, all that can be done is to lower the values of 1/fC1 and ESR. However even if the values of 1/fC1 and ESR can be kept as small as possible, the term 8RDS-ON still dominates the limit of the maximum output current.
2VIN 1/fC1
IOUT 8RDS-ON 4ESR COUT
VOUT LOAD
Fig. 22 The equivalent circuit of charge pump
Layout Considerations
With the high switching frequency and transient currents of the SS6845G, careful consideration of PCB layout is important. To achieve the best performance, it is necessary to minimize the distance between every component and also to minimize the length of every connection and maximize the trace width. Make sure each device connects to an immediate ground plane. Fig. 23 to Fig. 25 show a recommended layout.
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SS6845G
SS6845G
Fig. 23 Top layer
Fig. 24 Bottom layer
Fig. 25 Topover layer
APPLICATION EXAMPLES
VIN CIN 2.2 1 2 3 VOUT GND SHDN U1 CAP+ VIN CAPSS6845G 6 5 4 CFLY1 0.22F VOUT COUT 2.2F
1 VOUT 2 GND VSHDN 3 SHDN U2
CAP+ VIN CAP-
6 5 4 CFLY2 0.22F
SS6845G
CIN, COUT : TAIYO YUDEN Ceramic Capacitor, CELMK212BJ225MG (X5R) (0805) CFLY1, CFLY2: TAIYO YUDEN Ceramic Capacitor, CEEMK212BJ224KG (X7R) (0805)
Fig. 26 Using two SS6845G in parallel to provide larger output current.
USB CIN 2.2F 1 2 3 VSHDN VOUT GND SHDN U1 CAP+ VIN CAPSS6845G 6 5 4 CFLY 0.22F
VOUT COUT 2.2F
CIN, COUT: TAIYO YUDEN Ceramic Capacitor, CELMK212BJ225MG (X5R) (0805) : TAIYO YUDEN Ceramic Capacitor, CEEMK212BJ224KG (X7R) (0805) CFLY1
Fig. 27 Regulated 5V from USB
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SS6845G
PHYSICAL DIMENSIONS
D
(unit: mm)
S Y M B O L
SOT-23-6 MILLIMETERS MIN. 0.95 0.05 0.90 0.30 0.08 2.80 2.60 1.50 0.95 BSC 1.90 BSC 0.30 0.60 REF 0 8 0.60 MAX. 1.45 0.15 1.30 0.50 0.22 3.00 3.00 1.70
A
E1
A1
E
A2 b c
A
A
e e1
SEE VIEW B
D E E1
b A2
WITH PLATING
e e1
A
c
BASE METAL SECTION A-A
L L1
A1
0.25
GAUGE PLANE SEATING PLANE
L L1
VIEW B
PART MARKING
PART NUMBER CODE: BO50P = SS6845GG
BO50P
PACKING: Moisture sensitivity level MSL3
3000 pcs in antistatic tape on a reel packed in a moisture barrier bag (MBB).
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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