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Texas Instruments How to Estimate the Output Voltage Range of the Charge Pumps in the TPS6510x Application notes
Application Report
SLVA918 – December 2017
How to Estimate the Output Voltage Ranges of the Charge
Pumps in the TPS6510x and TPS6514x Devices
Ilona Weiss
ABSTRACT
This application report details how to estimate the output voltage range of the charge pumps in the
TPS65100, TPS65101, and TPS65105 (TPS6510x) series but also in the TPS65140, TPS65141, and
TPS65145 (TPS6514x) series. It assumes the output current from each charge pump is 50 mA, or less.
Trademarks
All trademarks are the property of their respective owners.
1
Introduction
The TPS6510x and TPS6514x devices contain driver circuitry for a positive and a negative charge pump.
For the positive charge pump, these devices also include the diodes which usually need to be connected
externally. The device regulates the output voltage of the charge pumps, if the output voltage is in the
available range. The application circuit and the operating conditions set the available range of output
voltages.
The mathematics used in the estimation is not complicated; however, see Figure 2 and Figure 5 for quick
answers.
This application report is based on the standard application circuits from the data sheet of the TPS6510x
(SLVS496) and TPS6514x (SLVS277) devices.
2
Negative Charge Pump
Most application circuits use the one-stage negative charge-pump circuit shown in Figure 1. More than
one stage can be used to generate more negative voltages, but few LCDs need such negative voltages
and therefore they are not discussed here.
V(SUP)
Q8
Control
Circuit
DRV
V(VO2)
Q9
Copyright © 201 7, Texas Instrumen ts Incorpor ate d
Figure 1. One-Stage Negative Charge-Pump Circuit
The minimum (that is, most negative) output voltage that this circuit can generate is given by:
WHITESPACE
VO 2
(VO1 2 u VF IO2 u (2 u rDS(on)Q8 2 u rDS(on)Q9 ))
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TPS6510x and TPS6514x Devices
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(1)
1
Negative Charge Pump
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where
• VO1 is the output voltage of the boost converter (shown as V(SUP) in Figure 1)
• VF is the forward voltage of the diodes
• IO2 is the output current of the negative charge-pump
• rDS(ON)Q8 and rDS(ON)Q9 are the on-resistances of the supply circuit
WHITESPACE
•
•
•
VF = 0.5 V (taken from the data sheet of the BAT54 diode)
rDS(ON)Q8 = 4.3 Ω at IDS = 20 mA
rDS(ON)Q9= 2.9 Ω at IDS = 20 mA
(1)
diode)
WHITESPACE
The values of VF , rDS(ON)Q8, and rDS(ON)Q9 increase as the output current increases. The negative charge
pump in these devices operate with a 50% duty cycle, so the peak current in the diodes and the current
sink is two times the output current. Thus, for output currents up to 25 mA, the peak current is 50 mA and
WHITESPACE
The maximum (that is, least negative) output voltage of the negative charge pump is –2 V.
Maximum Negative Charge Pump Output Voltage VO2 - V
Figure 2 is a graphic representation of the range of output voltages the negative charge pump in the
TPS6510x and TPS6514x devices can generate as a function of the supply voltage VO1.
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
Single Stage Negative Charge Pump
IO2 = 20 mA
IO2 = 50 mA
-13
-14
5
6
7
8
9
10
11
12
13
Boost Converter Output Voltage VO1 - V
14
15
DP00
Figure 2. Negative Charge-Pump Output Voltage Range
Ensure that the output voltage of the negative charge pump in the application is in the gray area of
Figure 2. The light gray filling shows the additional level the charge pump can provide if the load is only up
to 20 mA.
(1)
2
The BAT54 diode is commonly used in charge-pump circuits, but other diodes are available. If using a different diode, use the correct
value for VF.
How to Estimate the Output Voltage Ranges of the Charge Pumps in the
TPS6510x and TPS6514x Devices
Copyright © 2017, Texas Instruments Incorporated
SLVA918 – December 2017
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Positive Charge Pump
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The bottom boundary of the gray area also shows the output if you try to generate an output voltage below
the available range.
For example, if VO1 = 11 V and you try to generate VO2 = –12 V, approximately –9.7 V is obtained (found
by following the VO1 = 11 V grid line up until it hits the bottom boundary of the gray area).
3
Positive Charge Pump
Many LCD applications can use the positive charge pump in a doubler configuration. Applications that
need a higher VO3 voltage (that is roughly 2 x VO1) than a doubler can generate must use a tripler
configuration.
3.1
Positive Charge Pump Doubler
To correctly use the doubler configuration of the positive charge pump connect the flying capacitor across
the pins C1– and C1+. Leave pins C2+ open and connect pin C2–/Mode to ground, as shown in Figure 3
V(SUP)
V(SUP)
Q3
Q5
Control
Circuit
C1Å
C2Å/Mode
Q4
Q6
V(SUP)
D3
D2
C2+
D4
C1+
OUT3
V(VO3)
D1
Copyright © 201 7, Texas Instrumen ts Incorpor ate d
Figure 3. Positive Charge-Pump Circuit in Doubler Mode
The maximum output voltage the doubler can generate is given by:
WHITESPACE
VO3(dbl) 2 u VO1 2 u VF 2 u IO3 u (2 u rDS(on)Q5 rDS(on)Q4 rDS(on)Q3)
(2)
where
• VO1 is the output voltage of the boost converter (shown as V(SUP) in Figure 3)
• VF is the forward voltage of the diodes
• Io3 is the output current of the charge pump
• rDS(ON)Q3 = 9.9 Ω at IDS = 20 mA
• rDS(ON)Q4 = 1.1 Ω at IDS = 20 mA
• rDS(ON)Q5 = 4.6 Ω at IDS = 20 mA
WHITESPACE
The minimum output voltage for a doubler is given by:
VO3(dbl)(min) VO1 2 u VF
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(3)
3
Positive Charge Pump
3.2
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Positive Charge Pump Tripler
If the application needs a higher voltage for VO3 than a doubler charge pump can generate, use the tripler
configuration shown in Figure 4. Connect an additional flying capacitor between pins C2–/Mode and C2+.
V(SUP)
V(SUP)
Q3
Q5
Control
Circuit
C1Å
Q4
Q6
C2Å/Mode
V(SUP)
D3
D2
C2+
D4
C1+
OUT3
V(VO3)
D1
Copyright © 201 7, Texas Instrumen ts Incorpor ate d
Figure 4. Tripler Positive Charge-Pump Circuit
The maximum output voltage of the tripler circuit is given by:
WHITESPACE
VO3(trp) 3 u VO1 4 u VF 2 u IO3 u (3 u rDS(on)Q5 rDS(on)Q4 rDS(on)Q3)
(4)
WHITESPACE
Where,
• VO1 is the output voltage of the boost converter (shown as V(SUP) in Figure 4)
• VF = 0.5 V (taken from the data sheet of the BAT54 diode)
• Io3 is the output current of the positive charge pump
• rDS(ON)Q3 = 9.9 Ω at IDS = 20 mA
• rDS(ON)Q4 = 1.1 Ω at IDS = 20 mA
• rDS(ON)Q5 = 4.6 Ω at IDS = 20 mA
NOTE: The data sheets of the TPS6510x and TPS6514x devices specify a maximum value for VO3
of 30 V. Even if the tipler charge pump indicates higher output voltages can be generated in
the application, the maximum output voltage is limited to 30 V.
The minimum output voltage for a tripler is given by Equation 2.
Figure 5 shows a graphical representation of the output voltages that these devices can generate doubler
and tripler configurations. The light gray area between indicates the additional headroom gained if the
output current is only up to 20 mA. In the second figure it is also indicated the area (red filling) that is not
available if you are using a tripler configuration.
4
How to Estimate the Output Voltage Ranges of the Charge Pumps in the
TPS6510x and TPS6514x Devices
Copyright © 2017, Texas Instruments Incorporated
SLVA918 – December 2017
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Positive Charge Pump
Maximum Positive Charge Pump Output Voltage VO3 - V
www.ti.com
30
28
26
24
22
20
18
16
14
12
10
Doubler Stage Positive Charge Pump
IO3 = 20 mA
IO3 = 50 mA
Minimum VO3
8
6
4
5
6
7
8
9
10
11
12
13
14
15
Maximum Positive Charge Pump Output Voltage VO3 - V
Boost Converter Output Voltage VO1 - V
DP00
30
28
26
24
22
20
18
16
14
12
10
Tripler Stage Positive Charge Pump
IO3 = 20 mA
IO3 = 50 mA
Minimum VO3
8
6
4
5
6
7
8
9
10
11
12
13
Boost Converter Output Voltage VO1 - V
14
15
DP00
Figure 5. Positive Charge Pump Output Voltage Ranges
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TPS6510x and TPS6514x Devices
Copyright © 2017, Texas Instruments Incorporated
5
Summary
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Ensure that the output voltage is in the gray area of Figure 5. The light gray filling shows the additional
level the charge pump can provide if the load is only up to 20 mA. The red areas are not available in the
according configuration.
The boundaries of each area also indicate what output results if an output voltage outside the available
range is generated. For example:
• If VO1 = 11 V and you try to generate VO3 = 24 V with a doubler stage charge pump, approximately
20.6 V is achieved (found by following the VO1 = 11 V grid line up until it hits the top boundary of the
gray area).
• If VO1 = 11 V and you try to generate VO3 = 16 V with a tripler charge pump, you will find that this is in
the red filled area. As a result, the device will regulate up to its minimum which is at about 20 V (found
by following the VO1 = 11 V grid line up to the red line).
4
Summary
The charge pumps in the TPS6510x and the TPS6514x devices can regulate the output voltage if it is in
the available range. Use Figure 2 and Figure 5 in this document to see the available output voltage range
of the application. If the application operates close to the edge of the permitted range, ensure the design
has enough margin to operate correctly under all conditions.
6
How to Estimate the Output Voltage Ranges of the Charge Pumps in the
TPS6510x and TPS6514x Devices
Copyright © 2017, Texas Instruments Incorporated
SLVA918 – December 2017
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