1 general feature

1.5A internal switch

The working input voltage from 4.4V to 36V

3.3V/(± 2%) reference voltage

[

[

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[

123]输出电压可调

1.235V至35V

低压差运行：100%负载

循环

500KHz内部固定频率

[ 123] voltage feedback

Volidation current operation

Internal current limit

Zero current suppression

Consumption

Synchronous

Feedback Protection

Disglement

Hot shutdown

1.1 Application: Consumer: set -top box, DVD, TV, video recorder, car

radio, radios LCD display

Networking: XDSL, modem, DC-DC

module

Computer: printer, audio/graphic card, disc, hard disk drive

Industrial : Charger, automobile battery DC-DC converter

Instructions

L5970ad is a switch voltage voltage with a power switch of 1.5A with a power switch of 1.5A As a device, it can be directed to the load depending on the application conditions. The output voltage can be set between 1.235V and 35V. The device uses the internal P-channel D-MOS transistor (the typical RDSON is 200M ) as a switching device to avoid using self-raising capacitors and ensuring efficiency. The internal oscillator fix the switching frequency to 500kHz to minimize the size of the external component. Its minimum input voltage is only 4.4V for 5V bus and is suitable for all computer -related applications. The pulse current restrictions of internal frequency modulation provides effective constant current short circuit protection.

Electric characteristics (TJ 25 ° C, VCC 12V, unless there are other regulations.)

Note : 1. Design guarantee

Functional description

The main internal block is shown in Figure 4, which reports the equipment box diagram. They are: voltage regulator supplying internal circuits. The 3.3V reference voltage from the regulator can be obtained from the outside.

Check the voltage monitoring circuit of input and internal voltage.

Full integrated sawtooth oscillator with a frequency of 500kHz

Two embedded current restricted circuits for controlling the flow of

power switch. The limit of the pulse -by -pulse current forced the power switch cycleTurn off if the current reaches the internal threshold, and the frequency migration device reduces the switching frequency to significantly reduce the duty occupation ratio.

Cross -guidance error release large.

The pulse width modulator (PWM) comparator and the relevant logical circuit internal force required for the driver.

High-voltage side drive of the internal P-MOS switch.

Forbidden blocks for spare operation.

Circuit to achieve heat protection function.

Power and reference voltage

Internal regulator circuit (as shown in Figure 2) from the start circuit, internal voltage pre -editing device, band gap benchmark voltage voltage The source and the bias block of the current to all modules. When the input voltage is increased and the device is enabled (prohibited to pins), the starter provides start -current to the entire device. Pre -regulator block provides a pre -regulating voltage VREG for the gap unit, which has a very low voltage power supply voltage noise sensitivity.

voltage monitor

Internal block continuous sensing VCC, VREF and VBG. If the voltage is higher than the threshold regulator, start working. There is also a lagging phenomenon on the VCC (UVLO)

oscillator and synchronizer

FIG. 6 shows the frame diagram of the oscillator circuit. The clock generator provides the switch frequency of 500kHz device inside. When the frequency is strong or short -circuited, the block replacement block plays a role in reducing the frequency of the switch. The clock signal is then used for internal logic circuits, which is the input of the slope generator and the synchronization block. The slope generator circuit provides a sawtooth wave signal to achieve PWM control and internal voltage feedback, and synchronous signals generate synchronized circuits. In fact, this device has a synchronous tube foot that can be used as the main device and the device. As the internal switching frequency of the external device synchronous external device. Synchronize as an external signal as a slave. In particular, when the two devices are connected together, the device with a lower switching frequency is used as a component and another. To synchronize the device, the synchronous pipe foot must be transmitted from low level to the threshold of the level between 10%and 90%higher than the synchronous level, which depends on the frequency and amplitude of the signal. The frequency of synchronous signals must be at least higher than the device (500kHz).

current protection

L5970ad has two current limits protection, which is folded by pulse and frequency. Figure 7 shows the current -limited circuit schematic diagram of the current -protected current. The output power PDMOS transistor is divided into two parallel PDMOS. The smallest is a series of resistors, Rissen. The current is detected by the RSENSE. If the threshold is reached, the rearview mirror is unbalanced, and the PDMOS is turned off until the next drop edge of the internal clock pulse. Due to the reduction of the connection time, the output voltage is reduced. Because the minimum connection time (the necessary to avoid false overcurrent signals) is not enough to be at 50Get a sufficiently low duty ratio at 0KHz, so the output current may increase again under strong overcurrent or short -circuit conditions. Due to this, the switching frequency has also been reduced, so the electric sensor current is lower than the maximum threshold. The frequency shift (see Figure 6) depends on the feedback voltage. As the feedback voltage decreases (due to the decrease in the duty ratio), the frequency of switching also decreases.

Error amplifier

Voltage error Player is the core of the ring regulation. It is a non -inverter input connection to the internal reference voltage (1.235V), and the inverter input (FB) is connected to the external compressor or directly connected to the output voltage. The output is connected to the external compensation network. The unprecedented error release large device has the following characteristics:

Error amplifier output compares with the oscillator sawtooth wave to achieve PWM control.

PWM comparator and power level

This block of the oscillator serrated waves and an error amplifier output signal of the PWM error amplifier. Power level is a very critical module, because it must ensure the correct switch of PD MOS

Power component opening, or to better say, the rise time of the current when turning on is a very critical compromise parameter Essence In the first method, the faster the rising time, the lower the loss. But there is a limit on the recovery time of the cycle diode. In fact, when the current of the power component is equal to the current of the inductor, the diode is turned off, and the power of the drain is free. However, within the recovery time, the diode can be considered as a high -value capacitor to generate a very high peak current, which leads to many problems: the peaks on the equipment power supply voltage cause oscillation due to the parasitic of the circuit board (thereby generating noise). Passing the current will reduce efficiency and system reliability. Electromagnetic interference. Short the life span of the two -pole pipe. The current decrease time during the cutting period is also critical. In fact, it produces a voltage peak (due to parasitic elements on the board) to increase the voltage drop on PDMOS. In order to reduce all these problems, a new driving circuit topology is adopted, and its square diagram is shown in Figure 8. Its basic idea is based on PDMOS status and door clamp state. This circuit allows quickly turn off and turns on the power switch, and manages the above -mentioned related problems for the recovery time of the renewal binary pipe. The door clip is necessary to avoid the internal switch higher than VGSMAX. Open/risk control blocks can avoid any cross -conduction between the power cord and the ground.

The inhibitory function

The prohibited function allows the device to place the device in the standby mode. When INH PIN is higher than 2.2V, the device is disabled and the power consumption is reduced to less than 100 μA. When INH PIN is less than 0.8V, the device is enabled. If the INH pin is kept floating, the internal pull can ensure that the voltage on the pin is inhibitedThreshold, device is disabled. This pin is also compatible with VCC.

Hot turnover

If the chip temperature rises, the closing block will generate a signal that turns off the power level higher than the fixed internal threshold (150 ° C). The sensor element of the chip is very close to the PDMOS area, so ensure accurate and fast temperature testing. About 20 ° C dehination can avoid the continuous opening and closing of the equipment

additional functions and protection

Feedback disconnection

In the case of feedback disconnection, the duty cycle ratio is the largest The allowable value is increased so that the output voltage is close to the input power supply. This situation may destroy the load. In order to avoid this dangerous situation, if the feedback pipe keeps floating, the device is turned off.

Output overvoltage protection

Overvoltage protection OVP is achieved by an internal comparator. The input terminal and feedback of the comparator is turned off when the OVP threshold is reached. This threshold is usually 30%higher than the feedback voltage. When requiring the pressure division to adjust the output voltage (see the test application circuit), the OVP ventilation will be set to:

where R1 is connected between the output voltage and feedback pins The resistor, and R2 is connected to feedback stitches and ground.

empty load

Since the internal power supply is PDMOS, there is no need to increase the capacitor, so the device can work normally without loading at the output end. In this case, it works in an emergency, random repetition.

Application ideas

L5970ad belongs to the L597X series.

Related part numbers:

l5970d: 1.5A (ISW), 250kHz antihypertensive DC-DC converter, so8

l5972d: 2a (ISW), 250kHz dropped down Pressing DC-DC converter, so8

l5973ad: 2A (ISW), HSOP8 500KHz antihypertensive DC-DC converter

l5973d: 2.5A (ISW), 250kHz in HSOP8 antihypertensive antihypertensive voltage pressure DC-DC converter

If a higher current is required, the recent DC-DC converter series is L497X.