Features

Maintain a constant frequency under low output

Dual N -channel MOSFET synchronous driver

A programmable fixed frequency (PLL can be locked)

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123] Wide VIN range: 3.5V to 36V operation

Low minimum connection time (≤300NS) High frequency, low -occupation ratio application

Extremely low voltage drop operation: 99%LD Compared with

low pressure difference, 0.5A linear regulator, for CPU I/O or low noise audio equipment

Built -in -power power resolution timer

Aerable soft start [ 123]

Low -power detector

Remote output voltage detection

Folding flow limit (optional)

Pinnar available output voltage

[123 ] Logic control micro -power shutdown: IQ LT; 25μA output voltage from 1.19V to 9V

Provides 24 -draw narrow ssop and 28 -drawing SSOP package

Application software u

Notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks and notebooks Palm computer, PDA

mobile phone and wireless modem

Portable instrument

battery power supply equipment

DC power distribution system

Explanation [

explanation [ 123]

LTC #174; 1436A/LTC1437A is a synchronous anti -pressure -driven external switch regulator controller fixed phase lock N -channel power MOSFET frequency architecture. The adaptive PowerTM output stage selectively drives the two N -channel MOSFETs up to 400kHz in the frequency, while reducing the high efficiency of switching loss and low output current. Use an external PNP 0.5A auxiliary linear regulator PASS device to provide a source of low noise and low voltage difference. The second winding feedback control pins (SFB) can ensure that the adjustment can be used for compulsory continuous operation output regardless of the main load of the main load. An extra comparator can be used as a low battery detector. Including the signal of a delay of 65536/FCLK (300MS) is usually), the output voltage is generated when the signal of a delay of 65536/FCLK (300MS) is usually output. The internal resistor division provides a remote sensing capacity for the selected output voltage that can be selected. Users can detect the resistor through external current. The wide input power range allows working within the range of 3.5V to 30V (maximum 36V).

Absolutely maximum rated value

Input power supply voltage (VIN) 36V to –0.3V

The power supply voltage of the upper module driver (boost) 42V to —0.3V

Switch voltage (SW) VIN+5V to -5V

EXTVCC voltage 10 volt to -0.3 volts

POR, LBO voltage 12V to 0.3V

AUXFB voltage 20V to 0.3V

AUXDR voltage 28V to -0.3V

sensing+, sensing-, sensing voltage INTVCC+0.3V to -0.3V

VPROG voltage Intvcc ]

PLL LPF, ITH voltage 2.7V to –0.3V

Oakson, Prince, SFB, run/ss, LBI voltage 10V to — 0.3V

Peak driver output Current lt; 10μs (TGL, BG) 2A

Peak driver output current lt; 10μs (TGS) 250 mAh

intVCC output current 50 mAh

The working temperature range

LTC143XAC 0 ° C to 70 ° C

LTC143XAI – 40 ° C to 85 ° C

Jacking temperature (Note 1) 125 degrees Celsius

Storage storage Temperature range -65 ° C to 150 ° C

Lead temperature (welding, 10 seconds) 300 degrees Celsius

Electric characteristics TA u003d 25 ° C, vin u003d 15V, vRun/ss u003d 5V, Unless there is another instructions

Electric characteristics TA u003d 25 ° C, vin u003d 15V, vRUN/SS u003d 5V, unless there are other instructions.

indicates the standard temperature range suitable for the entire operation.

LTC1436ACGN/LTC1436ACGN-PLL/LTC1437ACG: 0 ° C ≤ TA ≤ 70 ° C

LTC1436AIGN/LTC1436AIGN-PLL/LTC1437Aig: -40 ° C ≤ 85 ° C

Note 1: TJ calculates according to the ambient temperature TA and power

Disposal PD according to the following formulas:

LTC1436ACGN/LTC1436ACGN-PLL/LTC1436AIGN/

LTC1436AIGN-PLL : TJ u003d TA+(PD) (110 ° C/W)

LTC1437ACG/LTC1437Aig: TJ u003d TA+(PD) (PD) (PD) (PD) (PD)95 ° C/W)

Note 2: LTC1436A/LTC1437A Test

The balance point of the servo Vosense to error amplifier (vitamin u003d 1.19V).

Note 3: Since the grid charge is transmitted at the switch frequency. View application information Section 1.

Note 4: By measuring COSC charge and discharge current and application formula:

Note 5: The auxiliary regulator tests the balance point of the error amplifier in the servo circuit. For

Vauxdr GT; 9.5V, Vauxfb uses internal resistor division. Do you see the application information?

Note 6: The minimum connection time test condition corresponds to 40%of a inductor peak ripple current ≥IMAX (see the precautions of the minimum connection time application information part)

Typical typical Performance features

pins function

vin: main power supply foot. The signal of the IC must be grounded.

INTVCC: Internal 5V regulator and EXTVCC output switch. The driver and control circuit consists of this voltage. Counterattack with the power supply must contain at least 2.2 μF or electrolytic capacitors. The bottom MOSFET driving power supply voltage.

EXTVCC: Input connected to the internal switch of INTVCC. This switch is turned off and provided VCC power EXTVCC higher than 4.7V at any time. See the EXTVCC connection application information part in the reference. Do not exceed 10 volt when you turn on. If VOUT ≥ 5V, connect to VOUT.

Production: Power supply to the upper module. The guide program electric container returns to this pin. The voltage swing at this pin from INTVCC to VIN+INTVCC. Open the underwriting node to the inductor. The voltage pins are lowered to the vehicle identification number from the voltage of the Schottky diode (external). Small signal ground. The ( -) terminals must be wiring separately from other ground to COUT.

PGND: Drive power ground. Connected to the ( -) end of the MOSFET and CIN at the bottom of the source.

Sense -: The current comparator ( -) input.

Sense+: (+) input of current comparator. The built -in offset between Sense and Sense+feet uses RSENSE to set the current check threshold.

Vosense: Receive the entire output of the remote sensing feedback voltage from the output or external resistor division. VPROG pin determine which VosenSE must be connected.

Vprog: This voltage selects the output voltage. For VPROG LT; Vintvcc/3, use Vosense to set the output to 3.3V to the output end. When Vosense is connected to the output when VPROG GT; VinTVCC/1.5, the output is set to 5V. Keep the Vprog open (DC) to allow the output voltage to set up by the external resistor division connected to Vosense. COSC: The frequency of external capacitors from this pin to grounding device works.

ITH: Error Putting Maca compensation points. The current comparator threshold increases with the increase of the control voltage. The nominal voltage range of this pin is 0 to 2.5 volts.

RUN/SS: The combination input of soft start and operation control. The capacitor sets the slope time to the full current output at this pin ground. The time is about 0.5s/μF.

Forcing this pin below 1.3V will cause the device to close and lie down. All functions are disabled when they are shut down.

TGL main channel: high -current door MOSFET. This is a voltage switching on the velocity switch at the opening node.

TGS: MOSFET, a large current door driver for small top N channels. This is the voltage switch with a stacked voltage. Keep the TGS open state operation to call the mode operation under the low load current.

BG: MOSFET, a large current door driver at the bottom N channel. The voltage swing at this pin is from ground to INTVCC (DRVCC).

SFB: Second winding feedback input. Under normal circumstances, the secondary winding of the feedback resistor division is used.

This pin should be connected to: grounded forced continuous operation; INTVCC is used to do not use secondary winding; and the output of secondary winding in the application.

POR: N -channel drop output. The output voltage rose to -5%of its specified value after the output voltage was adjusted and released the 65536 oscillator cycle. This time when run/ss is low independence, Por output is for you.

LBO: The leakage output of the drop of the N channel. When the LBI pin is lower than 1.19V, the pin will absorb current.

LBI: (+) input of low battery voltage comparator. ( -) Input connection to 1.19V reference voltage.

PLLIN: The external input of the phase detector. The pin is connected to SGND at the internal end with 50K #8486; The tie is not using the lock ring.

Locking loop LPF: The output of the phase of the phase is output and control the input oscillator. Usually the series of RC low -pass filter network is from this pin. Tie this needle in SGNDDo not use the application of locking loop. It can be driven by 0V to 2.4V logic signal for frequency transformation options.

AUXFB: The feedback input/comparator of the auxiliary regulator. When used as a linear regulator, this input can be connected to an external resistor division or directly connected to the collector 12V operation of the external PNP transmission device. When used as a comparator, it is the non -reversible input of the reverse input comparator connect to the internal 1.19V reference voltage. See the regulator/comparator in the auxiliary application information part.

Oakson: Open this big needle to open the auxiliary regulator/comparator. The threshold is 1.19V.

AUXDR: The opening output/comparator of the auxiliary regulator. The basis of the external PNP device is to connect to this pin as a linear regulator. An outer puller -pulling resistor needs to be used as a comparator. Auxdr's voltage greater than 9.5V causes the internal 12V resistor to connect to Auxfb.

Operation (reference function map)

Main control circuit

LTC1436A/LTC1437A adopts a constant frequency and current mode antihypertensive architecture. During the normal operation, when the oscillator is set to the RS memory, the main current comparator I1 reset the RS lock. The inductor current of the top I1 reset the RS lock is controlled by the voltage on the I pin, which is the wrong output amplifier EA. VPRGM and Vosense pins, as described in the pin, allow EA to receive the output feedback voltage VFB from the inside or external resistor division. Increased load current will cause VFB compared to 1.19V reference voltage, which in turn leads to an increase in the I voltage, until the average electrical sensor current matches the new load current. When the top of the top MOSFET is closed, the bottom MOSFET is opened until one of the inductors current starts to reverse, such as the current comparator i2, or the start of the next cycle. The MOSFET driver at the top comes from the floating startup with a capacitor CB, usually in each turnover cycle. However, when the vehicle recognition number (VIN) is approached to VOUT, the cycle may enter the Dropout and try to continue to open the top MOSFET. Attenuation detector calculates the oscillating cycle MOSFET keeps opening, and periodic forced to close the time to allow CB to charge. Low the main control circuit by pulling the RUN/SS pins. Release the RUN/SS allows the internal 3 μA current power supply to charging soft startup capacitor CSS. When the CSS reaches 1.3V, the main control loop enables the clamp voltage by ITH to be about 30%of its maximum value. As CSS continues to charge, the iTH is gradually rented again, allowing normal operations. The comparator OV prevents the transient super adjustment gt; 7.5%off the top MOSFET and keep it off until the fault is eliminated.

Low -current operation

The adaptive power mode allows LTC1436A/LTC1437A to automatically switch different load current between the two output levels. TGL and BG pin drive large high -power synchronization N -channel MOSFET current, while the current of the TGS pin drive is much smaller than the N -channel MOSFET low -current running diode used by Schottky. This allows the circulation to continue to use normal frequency as a decrease in the load running current without generating a large MOSFET door charge loss. If the TGS pin is kept open, the ring road defaults to the emergencies operation, where the MOSFET is intermittently operated according to the load requirements. The adaptive power mode provides a constant frequency operation, which is reduced to about 1%of the rated load current. This causes a load current to reduce a order of magnitude before the emergency mode operation begins. There is no small MOSFET (that is, no adaptive power mode), and the transition to an emergency mode operation is about the rated load current. When the COM PARTOR I2 detects the current reversal and close the bottom MOSFET. If the voltage on RSENSE exceeds the lagging complete cycle of I2 (about 20mV), and then in the next cycle, the top drive is disabled by the small MOSFET at the TGS pin and the BG pin. The peak peak of the electrical sensor exceeds 20mV/RSENSE or the i -i voltage exceeds 0.6V, so that the driver returns to the TGL pin in the next cycle. Even if the load current has other regulations, the two situations will be mandatory and continuously operate in the same operation. One is that the voltage of the co -mode Sense+and Sense -pins is lower than 1.4V, and the other is that when the SFB pin is lower than 1.19V, the condition is used to assist the secondary winding adjustment as described by the application information part.

Frequency synchronization

Locking loop (PLL) can allow the oscillator to synchronize to the connected external source PLLIN pin on the LTC1436A-PLL and LTC1437A. The output pins of the phase detector of the phase-locking loop low-pass filter are also the control input of the oscillator in the control input in the range of 0V to 2.4V, and the -30%frequency is 30%. When locking, the locking loop will align with the rise of the top MOSFET with the rising signal of the synchronous signal. When PLLIN keeps turning on or constant DC, the PLL LPF becomes lower, forcing the oscillator to minimize the frequency.

Operation (reference function diagram)

Powering and reset

POR pins are the leakage output of the road. When the output voltage rises within 7.5%of the adjustment, the timer starts and releases the Por (65536) oscillator cycle after 216. During the stop, the Por output was pulled down.

Auxiliary linear regulator

The auxiliary linear regulator in the LTC1436A/LTC1437A controls an external PNP transistor 500 mAh. A 12VThe AuxFB resistor division is higher than 9.5V to make the 12V VPP power supply easy to achieve. Auxdr is less than 8.5V external feedback allocation of other output voltages. Turn off the auxiliary regulator with the Oakson needle to provide a conversion logic control power supply. AUX block can be used as a comparator reverse input to connect to the internal 1.19V reference. This AUXDR pins are used as output, which requires the external pull to the power supply below 8.5V to suppress the calling internal resistor division. INTVCC/DRVCC/EXTVCC power supply top and bottom MOSFET driver and MOST power supply other LTC1436A/LTC1437A circuit. The bottom MOSFET driver is connected to the INTVCC outside the INTVCC external connection to the INTVCC outside the internal connection to the INTVCC in the LTC1436A. When EXTVCC pin keeps the road, the internal 5V low -voltage differential regulator is powered by INTVCC. If there is EXTVCC4.8V on it, the 5V regulator is turned off, and the internal switch is turned on to connect EXTVCC to INTVCC. This makes the INTVCC power supply comes from high -efficiency external sources, such as the output or secondary winding of the regulator itself, as described in the application information part.

Application information

The basic application circuit of LTC1436A is shown in Figure 1. High -efficiency antihypertensive converter. The selection of external components is driven by load requirements and starting from the choice of RSENSE. Once RSense knows, cosc u200bu200band I can choose. Next, choose MOSFETS and D1. Finally, CIN and COUT were selected. The circuit shown in Figure 1 can operate the operation of up to 28V input voltage (due to external MOSFET). The RSENSE of the output current selects RSENSE according to the required output current. The maximum threshold of the LTC1436A/LTC1437A current comparator is 150mv/rsense, and the mode range from the public line SGND to INTVCC. The current comparator threshold sets the peak of the electrical sensor current, which generates the maximum average output current IMAX equal to the peak value minus the peak ripple current #8710; IL. The change of LTC1436A/LTC1437A and external component values u200bu200bgenerate:

LTC1436A/LTC1437A and RSENSE value well ≥ 0.005 #8486; COSC for working frequency selection LTC1436A/LTC1437A uses constant frequency

frequency from the outside

oscillator capacitor. Each MOSFET on the upper part is opened, and the voltage on the COSC is reset to ground. On time, the COSC is an additional current phase detector V from a fixed current plus the output.Pllpf (LTC1436A-PLL) voltage/LTC1437A). When the voltage on the capacitor reaches 1.19V, COSC reset ground. Then repeat this process. The value of COSC is the frequency calculated based on the expected operation. Assuming that the oscillator is not locked:

The relationship between choosing cosc u200bu200band frequency is given. 2 As the operating frequency increases, the grid charge loss will be higher. , Reduce efficiency (see efficiency consideration). The recommended maximum switching frequency is 400kHz. When using Figure 2 to synchronize, select COSC corresponding to the frequency of 30%below the center. (See the synchronization of the loop and frequency of the locking loop.)

The value of the inductor value

The working frequency of the working frequency is related to the choice of the sensor, because it is higher, because it is higher The operating frequency allows the use of inductance and capacitance less. So why is anyone choosing a larger part of working at a lower frequency? The answer is efficiency. Higher frequency usually causes reduced efficiency because MOSFET grid charge loss. In addition to this basic balance, the impact of inductance value on the ripple current must also consider low -current operation. The inductance value has a direct impact on the ripple current. This inductance ripple current #8710; IL decreases with the increase of the inductance or frequency, and increases with the increase of VIN or VOUT:

Accept larger #8710; IL Value allows the use of low inductances, but can cause higher output voltage ripples and larger core losses. A reasonable starting point tidal wave current is #8710; IL u003d 0.4 (IMAX). Remember, the maximum #8710; IL appears under the maximum input voltage. The inductance value also affects low -current. Began to turn to low -current running as an inductor current to zero and the bottom MOSFET. The lower inductor value (higher #8710; IL) will occur under high load current to cause efficiency decreased operation within the upper limit range of low current. In the emergency mode operation (the TGS pin is opened), the lower inductance value will lead to a reduction frequency. Figure 3 gives the recommended induction value and operating frequency and voltage range

For the minimum connection time required for low -occupation ratio and high -frequency application, [123 123 ]

less than 350ns, which may be inductive to ensure normal work. For more details, please refer to the minimum boot time.

The electromat iron core selection

Once the value of L is known, the type of induction must be selected. High -efficiency converters can usually not bear the iron -hearted core of low -cost iron powder, forcing the use of more expensive iron oxygen, Molypermalloloy or KOOL MM #174; core. The actual iron heart loss is independent of the iron heart sizeThe fixed electromoter value, but it largely depends on the selected inductance. As an increase in inductance, the core loss decreases. Unfortunately, adding an inductance requires more threads, so the loss of copper will increase. The iron oxygen design has very low iron heart loss and is at high switching frequency, so the design target can be concentrated in copper loss and prevent saturation. The saturated ""hard"" of ferrite core material means that the peak design current exceeds. This caused the inductors to suddenly increase the ripple current and the output voltage ripples that came. Do not let the core saturate! Molypermalloy (from Magnetics, Inc.) Is a very low but more expensive iron oxygen than the material. The reasonable compromise solution of the same manufacturer is KOOL MM. The ring is very space -saving, especially when you can use several layers of wires. Because they usually lack wire shafts, it is difficult to install. However, the design of the surface paste is not significantly increased.

Power MOSFET and D1 select

You must choose three external power MOSFET for LTC1436A/LTC1437A: a pair of N channel MOS FET and a N channel for the top (main) switch for the top (main) switch MOSFET is used for the bottom (synchronous) switch. In order to use the adaptive power output level, the two must choose the upper module MOSFET. A large (low RSD (open)) MOSFET and a small (RDS (on)) MOSFET are compulsory. Use large MOSFET as the main switch and synchronous switch. Smaller MOSFET only enables the current situation under low load. This improves the efficiency of mid -current and continues to work at the same time at a constant frequency. At the same time, by using a small MOSFET circuit, it can be kept constant before the cycle, and the frequency operation is reduced to a lower current. The RDS (on) recommended by the small MOSFET is about 0.5 #8486; Be careful not to use RDS (on) too low; remember, we must save the door charge. (Higher RDS (ON) MOSFET has a smaller grid capacitor, so less current is required to charge the charging door). For cost -sensitive applications, small MOSFETs can be removed. The circuit will then start the operation when the load current decreases. The peak grille pole driver level is set by INTVCC. During the startup, the voltage is usually 5V (see EXTVCC pin connection). Therefore, most LTC1436A must use threshold MOSFET/LTC1437A. The only exception is that the application is that ExtVCC is greater than 8V by the external power supply (must be less than 10V), and which standard can use [VGS] less than 4th. Clear attention to the BVDSS specifications of MOSFETS AS specifications for many logic levels of MOSFET limited to 30V or less. The selection standard for power MOSFET includes the ""ON"" resistance RSD (ON), Reverse transfer capacitor CRS, input voltage and maximum output current.When the LTC1436A/LTC1437A runs the top and bottom MOSFET in the continuous mode: