CN105099158B

CN105099158B - A kind of soft starting circuit with fast response characteristic

Info

Publication number: CN105099158B
Application number: CN201510496751.1A
Authority: CN
Inventors: 明鑫; 艾鑫; 李天生; 付奎; 芮松鹏; 张波
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2015-08-13
Filing date: 2015-08-13
Publication date: 2017-07-21
Anticipated expiration: 2035-08-13
Also published as: CN105099158A

Abstract

The invention belongs to electronic circuit technology field, more particularly to a kind of soft starting circuit with fast response characteristic.The circuit of the present invention, the present invention is charged using step current to RC parallel-connection structures, and charging circuit includes current source I1, current source I2, the outer electric capacity C, resistance R1, resistance R2 of piece, comparator, the negative input for the pressure drop input comparator that switching tube MN, current source I1 are produced on resistance on R1, the negative input for the pressure drop input comparator that current source I2 is produced on resistance on R2, resistance R2 is in parallel with the outer soft start capacitor of piece, and is connected with MN1 drain electrode；Wherein current source I1 produces pressure drop V1 on resistance R1, is used as the positive input of the reference point input comparator of soft starting circuit voltage；Current source I2 charges to electric capacity C outside piece, the negative input of the voltage V2 input comparators on electric capacity；Comparator output soft start id signal then indicates that soft start-up process terminates for height, and chip enters normal operating conditions.

Description

A kind of soft starting circuit with fast response characteristic

Technical field

The invention belongs to electronic circuit technology field, more particularly to a kind of soft start electricity with fast response characteristic Road.

Background technology

In switch power technology field, soft starting circuit is very important module, can be applicable to DC-DC BUCK conversion In device, it is the process that slow upper electricity is provided for system that it, which is acted on, surge current occurs when anti-locking system is due to system electrification.

Traditional soft starting circuit common structure is as shown in figure 1, including comparator SS_COMP1, the outer electric capacity C, Yi Jijing of piece Image current source I1.

Assuming that electric capacity charges from no-voltage original state, the voltage on t electric capacity is determined by following formula：

V_{ss_in}C_ss=t × I_ss

I_ssFor current source I1 output currents；

As the charging voltage V on electric capacity_{ss_in}During equal to soft-start reference voltage SS_REF, soft start terminates：

Therefore obtaining total soft start (Tss) time is：

Electric current charges directly to electric capacity, it is ensured that the charging interval is most fast, but because soft start terminates (VSS_IN=SS_ REF after), electric current may proceed to electric capacity charging until the voltage on electric capacity is close to 5V (mirror current source close to linear zone).If After chip failure, NMOS tube MN1 grid control signals make MN1 conductings discharge soft start capacitor, until VSS_IN=SS_ REF, soft start comparator is overturn again.Require that the voltage on soft start capacitor discharges into 0.8V soft start marking signals from 5V Can just change, thus exist system close the response time it is longer, bring the potential safety issue under fault occurrences.

The content of the invention

It is to be solved by this invention, aiming above mentioned problem, propose a kind of soft start electricity with fast response characteristic Road.

To achieve the above object, the present invention is adopted the following technical scheme that：

As shown in Fig. 2 a kind of soft starting circuit with fast response characteristic, including the first current source I1, the second electric current Source I2, comparator, electric capacity C, NMOS tube MN, first resistor R1, second resistance R2 and 3rd resistor R3；The one of first current source I1 Termination power, its other end after first resistor R1 by being grounded；First current source I1 connects with first resistor R1 tie point to be compared The negative input of device；A second current source I2 termination power, the positive input and NMOS tube of its another termination comparator MN drain electrode；The output end of comparator is soft start id signal；NMOS tube MN grid connects external control signal, and its source electrode connects Ground；Second current source I2 and comparator positive input tie point pass through ground connection after second resistance R2；Electric capacity C and 3rd resistor R3 is in parallel with second resistance R2 after connecting, and electric capacity C is connected with the second current source I2 with second resistance R2 tie point, the 3rd electricity Hinder R3 ground connection.

The total technical scheme of the present invention, the present invention is charged using step current to RC parallel-connection structures, and charging circuit includes electricity Stream source I1, current source I2, piece outer electric capacity C, resistance R1, resistance R2, comparator COMP, switching tube MN, current source I1 is on resistance The pressure drop input comparator COMP produced on R1 negative input, the pressure drop input ratio that current source I2 is produced on resistance on R2 Compared with device COMP negative input, resistance R2 is in parallel with the outer soft start capacitor of piece, and is connected with MN1 drain electrode；Wherein electric current Source I1 produces pressure drop V1 on resistance R1, is inputted as the positive of reference point input comparator COMP of soft starting circuit voltage End；Current source I2 charges to electric capacity C outside piece, the negative input of the voltage V2 input comparators COMP on electric capacity；Comparator is defeated Go out soft start id signal SS_FLAG and then indicate that soft start-up process terminates for height, chip enters normal operating conditions.

Beneficial effects of the present invention are, it is adaptable to the soft starting circuit of DC-DC converter, are ensureing effective soft start-up process While, quick response turns off the ability of chip during with chip failure, and circuit is simple, and soft-start time is easy to control System.

Brief description of the drawings

Fig. 1 is prior art soft starting circuit schematic diagram；

Fig. 2 is soft start circuit structure schematic diagram of the invention；

Fig. 3 is soft starting circuit kernel model schematic diagram of the invention；

Fig. 4 changes over time oscillogram for the soft start voltage of the soft starting circuit of the present invention；

Fig. 5 is the soft start turn-off response schematic diagram of the soft starting circuit of the present invention.

Embodiment

As shown in Fig. 2 a kind of soft starting circuit with fast response characteristic of the present invention, including the first current source I1, Second current source I2, comparator, electric capacity C, NMOS tube MN, first resistor R1, second resistance R2 and 3rd resistor R3；First electric current A source I1 termination power, its other end after first resistor R1 by being grounded；First current source I1 and first resistor R1 connection Point connects the negative input of comparator；A second current source I2 termination power, the positive input of its another termination comparator With NMOS tube MN drain electrode；The output end of comparator is soft start id signal；NMOS tube MN grid connects external control signal, Its source ground；Second current source I2 and comparator positive input tie point pass through ground connection after second resistance R2；Electric capacity C with It is in parallel with second resistance R2 after 3rd resistor R3 series connection, and electric capacity C and the second current source I2 and second resistance R2 tie point company Connect, 3rd resistor R3 ground connection.

The present invention operation principle be：

The core circuit of the structure of the present invention can be equivalent to Fig. 3 charge model.After soft start-up process starts, t electricity Hold C on voltage be：

To simplify calculating, it is considered to t>0 situation, e (t)=1, and take approximation relation：

T=τ, V₂(t)=0.63I₂R₂

T=2 τ, V₂(t)=0.86I₂R₂

T=3 τ, V₂(t)=0.95I₂R₂

T=4 τ, V₂(t)=0.98I₂R₂

T=5 τ, V₂(t)=0.99I₂R₂

Wherein, τ=R₂C, I₂R₂Represent the steady state voltage value on electric capacity.

Charge total time M τ (M=1,2,3,4,5) and the voltage KI on electric capacity are obtained from above approximately relation₂R₂(K= 0.63,0.85,0.95,0.98,0.99 one-to-one relationship)

Formula is obtained by V2=V1=I1R1 again：

KI₂R₂=I₁R₁, because I1=I2, then KR₂=R₁。

Therefore, if R2 and R1 ratio R₂/R₁=K determines that then charging is also determined total time M τ.Above analytic explanation is soft to be opened The dynamic time is together decided on by the resistance ratio of RC time constants and R1 and R2.Then soft-start time can be carried out by plug-in capacitor C Setting, realizes soft-start time adjustable function.

Above-mentioned analysis realizes normal soft start-up process, it is considered to, need to be to soft when chip, which runs into failure, to be restarted Start-up capacitance discharges into zero, and soft start marking signal is dragged down, and waits chip to start next time.Therefore the reset time of soft start The turn-off response speed of influence system.Now analyze and exit soft start-up process to what electric capacity discharged.

In the discharge process of analysis conventional soft start structure first, Fig. 1, after soft start terminates, charging voltage VSS_IN ≈ 5V, when chip breaks down, NMOS tube grid control signal SS_RESET=1, MN1 conducting, MN1 is first operated in saturation region, VSS_IN reduces, and works as VSS_IN-VTH<Linear zone is operated in after 5V, VSS_IN discharges into VSS_IN<During SS_REF, soft start mark Know signal SS_FLAG upsets, then △ V=5-0.8=4.2V in discharge process.

In Fig. 2, the steady state voltage on electric capacity remains I₂R₂, by V2=I2R>V1, treats that chip runs into failure and needs shut-off When, SS_RESET signals are height first, and trigger switch pipe MN1 is opened, and soft start capacitor C is discharged by switching tube MN1.Switching tube MN1 turns on moment, VGS1=5V, VDS1 ≈ 0.8V, then VGS1-Vth>VDS1, MN1 are operated in linear zone, flow through switching tube Electric current is：

Discharge process, VDS1 persistently reduces, therefore VGS1-Vth>VDS1, MN1 always work in linear zone, until V2< V1, soft start marking signal is dragged down, and indicates that soft starting circuit is reset, and waits chip unlatching next time.During being somebody's turn to do, on electric capacity Voltage variety be △ V=V₂-V₁≈ 0.83-0.80=0.03V.

Wherein μ is channel carrier mobility；COX is the gate oxide capacitance of unit area；W/L is MOS breadth length ratios, under It is designated as referred to metal-oxide-semiconductor；VGS1 is poor for the gate source voltage of metal-oxide-semiconductor；VTH is the threshold voltage of NMOS tube.

In road from the above analysis, soft start circuit structure of the invention, when chip is turned off, the tension discharge on electric capacity To VSS<SS_REF can drag down soft start marking signal, wait chip startup next time.From chip shut-off is received to soft start Marking signal is reset, the voltage change range very little on soft start capacitor, therefore discharge time is very short, then substantially increases chip Turn-off response speed.

By the soft starting circuit of above-mentioned design, while effective soft start-up process is ensured, the shut-off for improving chip rings Between seasonable, and circuit structure is simple, and soft-start time is controllable.

Soft start circuit structure proposed by the invention, is emulated by SPECTRE and illustrated, resistance R1 and the R2 ratio in piece Determine the relation between soft-start time and RC parallel-connection structure time constants RC；Therefore when IC design it is packaged it Afterwards, electric capacity of the soft-start time of chip only outside piece is determined.After soft-start time terminates, comparator output logic SS_ FLAG is height, such as Fig. 4.When chip failure, it is necessary to which when restarting, SS_RESET logic control switch pipes MN1 is opened, and is given Soft start capacitor C discharges, and when V2=V1, drags down SS_FLAG, as can be seen from Figure 5, from reset signal is received to soft start mark Signal drags down the response time for 10ns, and response speed quickly, improves the security of chip in the case of failure.

Claims

1. a kind of soft starting circuit with fast response characteristic, including the first current source I1, the second current source I2, comparator, Electric capacity C, NMOS tube MN, first resistor R1, second resistance R2 and 3rd resistor R3；A first current source I1 termination power, its The other end after first resistor R1 by being grounded；The negative sense that first current source I1 and first resistor R1 tie point connects comparator is inputted End；A second current source I2 termination power, the drain electrode of the positive input and NMOS tube MN of its another termination comparator；Compare The output end of device is soft start id signal；NMOS tube MN grid connects external control signal, its source ground；Second current source I2 and comparator positive input tie point pass through ground connection after second resistance R2；Electric capacity C connected with 3rd resistor R3 after with Two resistance R2 are in parallel, and electric capacity C is connected with the second current source I2 with second resistance R2 tie point, 3rd resistor R3 ground connection.