1. Features

The working power supply voltage is 5V to 12V bus

up to 1.3A grid current capacity

The output voltage can be adjusted

n- Reverse E/A input can be available for

0.9V ± 1.5%reference voltage

voltage mode PWM control

Very fast load transient response

0 %To 100%duty cycle

Good output

Overwriting protection

HICCUP over current protection

200kHz internal oscillator

[123 ] External adjustable oscillator

from 50kHz to 1MHz

Soft start and inhibition

Packaging: SO-16

2. Application

[

[ 123] The supply of memory and terminology

Computer additional card

Low-voltage distributed DC-DC

Magnetic amplifier replacement

3. Explanation

This device is a high-performance PWM controller from DC-DC conversion from 3.3V, 5V and 12V bus. The output voltage can be adjusted to 0.9V; the external power supply can be used to obtain a higher voltage division. The peak current door driver provides fast switching to the external power supply part, and the output current can exceed 20A. This device ensures the protection of overload and overvoltage. It also provides an internal crowbar to turn on the low -side MOSFET. As long as the voltage is detected, once the current is detected, the capacitor discharge is soft, and the system work snoring mode

Table 5. Electrical characteristics (VCC u003d 12V, TJ u003d 25 ° C, unless there are other regulations)

Device description

This device is an integrated integrated with BCD technology. Circuit. The controller provides complete control logic and protection for high-performance antihypertensive DC-DC converters. It is designed to drive the channel MOSFET in the buck topology. The output voltage of the converter can be used as the internal reference value (simply connecting Earef and VREF pin). The device also allows external reference voltage (0.9V to 3V). The device provides a fast transient voltage mode control response. It includes a 200kHz free running oscillator, which can be adjusted from 50kHz to 1MHz. The error amplifier has a 10MHz gain bandwidth and the conversion rate of 10V/μs, which can achieve high converter bandwidth and achieve fast transient performance. The range of PWM duty ratio is 0%to 100%. This device prevents over -current from entering the fault mode. AssumePrepare the upper MOSFET RDS (on) monitoring current without the need for a current. The device has SO16 narrow packaging.

oscillator

The switching frequency is fixed to 200kHz internally. The internal oscillator produces triangular waveforms to PWM charging and discharge and constant current capacitors. The current is usually 50 μA (FSW u003d 200kHz), which can be connected to an OSC pin and GND or VCC. Because the OSC pin is maintained at a fixed voltage (typical. 1.235V), the current of the frequency and the pins (pressing) is proportional to change. Especially when connecting RT and GND, according to the following:

When connecting the RT to VCC u003d 12V or VCC u003d 5V, the frequency decreases (the current is forced to enter the pins) According to the following relationship:

The switch frequency change vs.rt repeat in Figure 4. Please note that when you apply a 50μA current to the pin, the oscillator is passed to the oscillator because there is no current

Reference

Provides accurate ± 1.5%0.9V 0.9V Reference voltage. The reference value must be filtered with 1NF ceramic capacitor to avoid the instability of the internal linear regulator. It can provide a current of up to 100 μA, which can be adjusted as a device, and it is also suitable for other equipment. If it is forced at 70%of its nominal value, the device enters the HIC CUP mode until the condition is eliminated. You can get regulatory reference through EareF pin. This pins directly connect to the input of non -inverse errors. External reference (or internal 0.9V ± 1.5%) can be used. The range of this input pin from 0.9V to 3V. It has an internal pull -down (300K resistance), if the reference is not connected (the pin is floating). However, if the voltage on the EareF pin is less than 650mv (typical values).

Soft start

When starting, a slope will be generated, and the external capacitor CSS is charged with an internal current generator. The current value of the first letter is 35 μA, and the charging speed of the capacitor is increased to 0.5V, and then the capacitor becomes 10 μA until the final charging value is about 4V. When the voltage on the soft startup capacitor (VSS) reaches 0.5V, the low -power MOS is turned on and the output capacitor discharges. When the VSS reaches 1.1V (that is, the lower limit of the oscillator triangle wave), the upper limit MOS starts the switch and the output voltage begins to increase. If the SS keeps below 0.5V and the two MOSFETs are closed, the switching activities are not observed. If the VCC and Ocset pin does not exceed its own opening threshold, and the Vearef is not higher than 650mV, the soft start will not occur, and the related pins will be short -circuited to the GND. During normal operation,If any underwriting voltage is detected on one of the two power supply, the SS pin is short -circuited inside the GND, so the SS capacitor is quickly discharged.

The driver's room

The driver capacity of high, low -pressure drive allows the use of different types of power MOS (can also reduce RDSON) Quick switch conversion. The low -voltage side MOS driver is directly provided by VCC, and the high -voltage side drive is provided by the starting pin. Using adaptive dead zone control to prevent cross -conductors and allow multiple types of MOS FETs. When the grille is greater than 200mv, the upper MOS is avoided, and the lower MOS is turned on to avoid if the phase pins exceed 500 millivolta, it should be avoided. In any case, the lower MOS is closed on the high -voltage side. At 5V and 12V, the peak currents of the upper part (Figure 6) and the lower part (Figure 7) are displayed. The 3.3NF capacitor load was used in these measurements. For lower drivers, the source peak current is 1.1a@vccu003d12v and 500ma@vcc u003d 5V, while the Sink peak value is 1.3A@vcc u003d 12V, 500ma@vcc u003d 5V. Similarly, for the upper -layer driver, the source peak current is 1.3a@vboot vphase u003d 12V and 600MA@vboot VPHase u003d 5V, and the peak of the trap is 1.3a@vboot vphase u003d 12V and 550ma@vboot vphase u003d 5V.

Excessive current protection is performed by a device with a high voltage side MOS voltage drop, because the voltage of the external resistance (ROCS) is connected to the OcSet pin and Shangmos. Therefore, over -current threshold (IP) can be calculated through the following relationship:

When the typical value of IOCS is 200 μA. To calculate the ROCS value, it must be regarded as the maximum value of RDSON (also changes with temperature) and the minimum value of Iocs. In order to avoid accidental trigger current protection, this relationship must be satisfied:

Type #8710; i is an inductive ripple current, and iOUTMAX is the maximum output current. If the current is detected, the soft startup capacitor will be discharged at a constant current (typical value of 10 μA), and the SS pin reaches the 0.5V soft start phase. During the soft startup process, overcurrent protection is always in a state of activity. If such incidents occur, the device will turn off two MOSFETs, and the SS capacitor will be powered off again (after reaching the upper limit of about 4V). The system now works in the ""snoring"" mode, as shown in Figure 8. After the reasons for overcurrent, the device restarts the normal working power switch.

inductor design

The inductance value is defined by the transient response time, efficiency, and the compromise between the cost. The inductor must be calculated to maintain the output and maintain the input voltage change ripple current #8710; IL between 20%and 30%of the maximum output current. The inductance value can be calculated through the following relationship:

Among them, the FSW is the switch frequency, VIN is the input voltage, and VOUT is the output voltage. Figure 9 shows the ratio of the output voltage of the ripple current to the output voltage of different inductance values u200bu200bwhen Vin u003d 5V and Vin u003d 12V. Increasing the electrical value will reduce the ripple current, but it will also reduce the transient response time of the converter load. If the compensation network design is good, the device can open or close the duty ratio up to 100%or drop to 0%. The response time is now the time required to change its current value from the initial value to the final value. Since the inductor has not completed the charging time, the output current is provided by the output capacitor. The shorter the response time, the smaller the output capacitance.

The response time of the load transient state is different due to the application of the load: if the load is applied, the inductor is equivalent to the voltage charging voltage between the input and output. Discharge from the output voltage. The following expression gives the compensation network response fast enough #8710; i load transient approximate response time:

The worst situation depends on the available situation depends Input voltage and selected output voltage. In any case, the worst case is the response time after the load removal, the minimum output voltage is programmed, and the maximum input voltage is available.

Output capacitor

The output capacitor is the basic component of the rapid response of the power supply. In fact, in the process of load transmission, in the initial micro seconds, they provide current to the load. The controller immediately identifies the load transient and sets the duty cycle to 100%, but the current slope is limited by the inductor value. Due to the changes in the current in the capacitor, the voltage decreases for the first time (ignored the impact of ESL):

During the load transient state, a minimum capacitor value is required to maintain the current without discharge. The voltage caused by the discharge of this output capacitor can be concluded through the following formulas:

Among them, DMAX is the maximum duty cycle, that is, 100%. The lower the ESR, the lower the output. The lower the static ripple of the output voltage during the transient transient.

Input a capacitor

Input capacitors must withstand the ripple current generated during the upper MOS drive, so it must have a low ESR to minimize the loss. The RMS value of this ripple is:

Compensation network design

The control loop is voltage mode (Figure 10). OutputThe regulation is the input reference voltage level (EareF).Then compare the error amplifier output VCOMP with the oscillator triangle wave to provide the pulse width modulation (PWM) wave with VIN amplitude at the phase node.This wave is output filter.The modulator transmission function is a small signal transmission function of VOUT/VCOMP.This function resonates according to L-COUT, the frequency FLC is bipolar and FESR is zero, depending on the output capacitor ESR.The DC gain of the modulator is the input voltage VIN except the vosc of the input voltage vin #8710; VOSC.