L5970ADTR Datasheet L5970AD, L5970ADTR | P7-P9

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L5970AD

The turn on of the power element, or better, the rise time of the current at turn on, is a very critical param-

eter to compromise.

At a first approach, it looks like the faster it is the rise time, the lower are the turn on losses.

But there is a limit introduced by the recovery time of the recirculation diode.

In fact when the current of the power element equals the inductor current, the diode turns off and the drain

of the power is free to go high. But during its recovery time, the diode can be considered as an high value

capacitor and this produces a very high peak current, responsible of many problems:

Spikes on the device supply voltage that cause oscillations (and thus noise) due to the board parasitics.

Turn on overcurrent causing a decrease of the efficiency and system reliability.

Big EMI problems.

Shorter freewheeling diode life.

The fall time of the current during the turn off is also critical. In fact it produces voltage spikes (due to the

parasitics elements of the board) that increase the voltage drop across the PDMOS.

In order to minimize all these problems, a new topology of driving circuit has been used and its block dia-

gram is shown in fig. 8.

The basic idea is to change the current levels used to turn on and off the power switch, according with the

PDMOS status and with the gate clamp status.

This circuitry allow to turn off and on quickly the power switch and to manage the above question related

to the freewheeling diode recovery time problem. The gate clamp is necessary to avoid that Vgs of the

internal switch goes higher than Vgsmax. The ON/OFF Control block avoids any cross conduction be-

tween the supply line and ground.

Figure 8. Driving Circuitry

3.7 INHIBIT FUNCTION

The inhibit feature allows to put in stand-by mode the device. With INH pin higher than 2.2V the device is dis-

abled and the power consumption is reduced to less than 100

A. With INH pin lower than 0.8V, the device is

enabled. If the INH pin is left floating, an internal pull up ensures that the voltage at the pin reaches the inhibit

threshold and the device is disabled. The pin is also Vcc compatible.

Vgs

max

GATE

STOP

DRIVE

DRAIN

OFF

PDMOS

VOUT

DRAIN

VCC

LOAD

ESR

D00IN1133

OFF

ON/OFF

CONTROL

CLAMP

L5970AD

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3.8 THERMAL SHUTDOWN

The shutdown block generates a signal that turns off the power stage if the temperature of the chip goes higher

than a fixed internal threshold (150°C). The sensing element of the chip is very close to the PDMOS area, so

ensuring an accurate and fast temperature detection. An hysteresis of approximately 20°C avoids that the de-

vices turns on and off continuously

4 Additional Features and Protections

4.1 FEEDBACK DISCONNECTION

In case of feedback disconnection, the duty cycle increases versus the maximum allowed value, bringing the

output voltage close to the input supply. This condition could destroy the load.

To avoid this dangerous condition, the device is turned off if the feedback pin remains floating.

4.2 OUTPUT OVERVOLTAGE PROTECTION

The overvoltage protection, OVP, is realized by using an internal comparator, which input is connected to the

feedback, that turns off the power stage when the OVP threshold is reached. This threshold is typically 30%

higher than the feedback voltage.

When a voltage divider is requested for adjusting the output voltage (see test application circuit), the OVP inter-

vention will be set at:

Where R

is the resistor connected between the output voltage and the feedback pin, while R

is between the

feedback pin and ground.

4.3 ZERO LOAD

Due to the fact that the internal power is a PDMOS, no boostrap capacitor is required and so, the device works prop-

erly also with no load at the output. In this condition it works in burst mode, with random repetition rate of the burst.

5 Application Ideas

L5970AD belongs to L597x family.

Related part numbers are:

● L5970D: 1.5A (I

), 250KHz Step Down DC-DC Converter in SO8

● L5972D: 2A (I

), 250KHz Step Down DC-DC Converter in SO8

● L5973AD: 2A (I

), 500KHz Step Down DC-DC Converter in HSOP8

● L5973D: 2.5A (I

), 250KHz Step Down DC-DC Converter in HSOP8

In case higher current is needed, the nearest DC-DC Converter family is L497x.

OVP

1.3

--------------------

⋅⋅=

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L5970AD

6 Package Information

Figure 9. SO-8 Mechanical Data & Package Dimensions

OUTLINE AND

MECHANICAL DATA

DIM.

mm inch

MIN. TYP. MAX. MIN. TYP. MAX.

A 1.35 1.75 0.053 0.069

A1 0.10 0.25 0.004 0.010

A2 1.10 1.65 0.043 0.065

B 0.33 0.51 0.013 0.020

C 0.19 0.25 0.007 0.010

(1)

4.80 5.00 0.189 0.197

E 3.80 4.00 0.15 0.157

e 1.27 0.050

H 5.80 6.20 0.228 0.244

h 0.25 0.50 0.010 0.020

L 0.40 1.27 0.016 0.050

k 0˚ (min.), 8˚ (max.)

ddd 0.10 0.004

Note: (1) Dimensions D does not include mold flash, protru-

sions or gate burrs.

Mold flash, potrusions or gate burrs shall not exceed

0.15mm (.006inch) in total (both side).

SO-8

0016023 C

P1-P3 P4-P6 P7-P9 P10-P11

L5970ADTR

Mfr. #:

Buy L5970ADTR

Manufacturer:

STMicroelectronics

Description:

Switching Voltage Regulators STEP DOWN MONOLITHIC SWITCH REG 1.5A

Lifecycle:

New from this manufacturer.

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L5970ADTR

L5970ADTR

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