The hottest ultra-low input voltage boost DCDC con

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This paper introduces an ultra-low input voltage boost dc/dc converter tps61200 series. The minimum input voltage of this series is 0.3V within the working temperature range of ta=-40 ~ +85 ℃; A single chip can form a boost power supply with high efficiency. There are three models of this series, with output settable and fixed voltage output, as shown in Table 1

characteristics and application fields

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t12, beam speed conditioning range (mm/min):1 (5) the main characteristics of 00ps61200 series: high efficiency (when Vin is 1.2V, output is 3.3V, output current is 600mA, its efficiency can be greater than 90%); According to the size of the input voltage, it can be automatically converted to boost mode or step-down mode; Low static current (less than 55 A); When the input voltage is 0.5V, it can also start working at full load; The input working voltage range is wide, from 0.3 to 5.5V; The voltage of input low voltage latch can be set; Output short-circuit protection; There are varieties of output voltage that can be set and fixed for users to choose (see Table 1); When the output power is low, there is an energy-saving mode, which can improve efficiency; It is possible to force work at a fixed efficiency; When the power is turned off, the load is disconnected from the input end; Overheating protection; Operating temperature range -40 ~ +85 ℃; Small size 3mm 3mm QFN package

the main application fields of tps61200 series: electronic products that can be used for 1 ~ 3 alkaline batteries, nickel cadmium or nickel hydrogen batteries, or 1 lithium ion battery, lithium polymer battery or lithium iron phosphate battery; Electronic products powered by solar cells and fuel cells; Electronic products powered by solar cells and fuel cells; Portable audio player; PDA;; Personal medical electronic products (such as sphygmomanometers) and driving white LED, etc

for products using primary alkaline batteries, the battery voltage can be reduced to 0.5V, so as to make the best use of everything and improve the service life of the battery

pin arrangement and function

the pin arrangement of tps61200 series is shown in Figure 1, and the functions of each pin are shown in Table 2

Figure 1 pin arrangement of tps61200

main technical parameters

main limit parameters of tps61200 series: the input voltage is -0.3 ~ 7V (including VIN, l, Vaux, Vout, PS, en, FB, UVLO terminals). Recommended working conditions: vin=0.3 ~ 5V

tps61200 series main electrical characteristic parameters: adjustable output voltage is 1.8 ~ 5.5V; Fixed 3.3V output voltage tolerance 0.03V; Fixed 5.0V output voltage tolerance 0.05v; The internal average switching current is limited to 1350MA; Typical value of static current is 50 a; The power consumption is less than 2 A in the off state; En end low level: VIN < 0.1vin when Vin < 0.8V, < 0.4V when Vin > 1.5V, < 0.2vin when Vin 1.5V; EN high level: VIN > 0.9vin when Vin < 0.8V, > 1.2V when Vin > 1.5V, > 0.8vin when Vin > 1.5V; PS input low level < 0.4V, PS input high level > 1.2V; The switching frequency of the switch tube is 1250 ~ 1650khz

typical application circuit

for this reason, the typical application circuit of tps61200 is shown in Figure 2, and the application circuit of tps61201 and tps61202 is shown in Figure 3

Figure 2 typical application circuit of tps61200

Figure 3 application circuit of tps61201 and tps61202

Figure 2 is a circuit whose output voltage can be set. The output voltage Vout is related to the external resistance voltage dividers R1 and R2, as shown in the following formula:

vout=vfb (r1/r2 + 1) (1)

in the formula, vfb=500mv, R1 can be set to 1m, then the R2 value can be obtained. For example, if vout=3.3v is required, r2=178.57k can be obtained by substituting into the above formula, and the standard resistance value of 180 K can be taken

in Figure 2, en terminal, PS terminal and UVLO terminal are connected to VIN, which means that the power supply does not use en terminal plus low level to turn off the power supply; The high level of PS terminal indicates that it works under heavy load conditions (at this time, the oscillator works at a fixed frequency); UVLO is connected to VIN, which means that when Vin < 250 MV, the power is turned off, vout=0v, and latched; Only when Vin> 350mV, the power supply will resume operation

in Figure 2, Vaux is grounded at 0.1 f in order to work stably (the factory recommends that C3 use a multilayer elutriation capacitor with low equivalent series resistance, with a capacity of 0.1 f). When this capacitor is started, it will charge C3 to a certain value before the switch is turned on, which will buffer the switch. If the output voltage Vout is less than 2.5V. C3 value can be 1 F

c1 is the input capacitance, and its minimum value is 4.7 F. here, a 10 f multilayer ceramic capacitor is used. C2 is the output capacitance. The factory recommends that the following formula be used to select the C2 value:

c2=5l (f/h) (2)

if l=2.2 h, C2 can take 10 F. C2 also uses multilayer ceramic capacitors. Using a larger capacity C2 can reduce the output ripple voltage and reduce the transient load change. I hope the above sharing can help you correctly use the output voltage drop caused by this equipment

the value of inductor L1 in Figure 2 can be estimated by the following formula:

lmin=vin 0.5 s/a (3)

generally, L1 is taken between 1.5 ~ 4.7 h, which has good performance in the whole range of input voltage and output voltage

Figure 3 shows the application circuit of fixed output voltage. In the figure, only FB and Vout are connected, and other parts are in phase with figure 2 (not shown in Figure 3)

if the low-voltage latch voltage threshold of the input voltage needs to be set, the set low-voltage latch threshold voltage vinmin is related to the external resistance voltage dividers R3 and R4, as shown in the following formula (circuit is shown in Figure 4):

Figure 4 tps61200 input voltage latch circuit

vinmin/(r3+r4) = vuvlo/R4 (4)

where vuvlo=250mv. It is recommended that R4 be taken as 250K, and then R3 can be calculated after setting vinmin value. When Vin is lower than vinmin, the output is turned off (vout=0v)

for example, if vinmin is 1V, r4=250k, vuvlo=250mv, r3=750k can be obtained

efficiency under different working conditions

tps61201 and tps61202 have different efficiency under different working conditions. Here are some typical characteristic curves. Figure 5 shows the efficiency curve of tps61202 with different input voltage and output current when it adopts energy-saving mode (PS terminal grounding). Figure 6 is the efficiency curve of different input voltages and different output currents when the same tps61202 does not adopt the energy-saving mode (PS terminal high level). From the comparison between figure 5 and Figure 6, it can be seen that when the output current io=10ma and the input voltage Vin is 1.5 ~ 3V, the efficiency of adopting energy-saving mode is much higher than that of not adopting energy-saving mode, that is, under the working conditions of light load, adopting energy-saving mode has higher efficiency. For example, when vin=2v and io=10ma, the efficiency with energy-saving mode is 78%, while that without energy-saving mode is 5.3%. When the load is heavy, such as io=500ma, there is little difference between the energy-saving mode and the non energy-saving mode

Figure 5 efficiency of tps61202 in energy-saving mode

Figure 6 efficiency of tps61202 without energy-saving mode

Figure 7 and figure 8 are the efficiency curves of tps61201 with and without energy-saving mode. From the comparison between Figure 7 and figure 8, it can be seen that when io=10ma, the efficiency is improved by adopting the energy-saving mode in the VIN range of 1 ~ 2.5V. For example, when vin=2v, the efficiency of Figure 7 is about 76%; The efficiency of figure 8 is only 60%; When io=100ma, the efficiency of adopting energy-saving mode is lower than that of not adopting energy-saving mode in the range of VIN from 1 to 2.5V. For example, when io=100ma and vin=2v, the efficiency is about 76% when the energy-saving mode is adopted; Under the same conditions, the efficiency of non energy saving mode is about 88%

Figure 7 efficiency of tps61201 with energy-saving mode

figure 8 efficiency of tps61201 without energy-saving mode

from the above situation, efficiency can be improved only when energy-saving mode is adopted under light load; When the load current is large, the effect of adopting energy-saving mode is not good

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