Datasheet

ManualsBrandsSTMICROELECTRONICS ManualsPMICsPMIC - DC/DC voltage regulator Holder SO 8

1/11

L5970AD

March 2005

1 General Features

■ 1.5A INTERNAL SWITCH

■

OPERATING INPUT VOLTAGE FROM 4.4V TO 36V

■ 3.3V / (±2%) REFERENCE VOLTAGE

■ OUTPUT VOLTAGE ADJUSTABLE FROM

1.235V TO 35V

■ LOW DROPOUT OPERATION: 100% DUTY

CYCLE

■ 500KHz INTERNALLY FIXED FREQUENCY

■ VOLTAGE FEEDFORWARD

■ ZERO LOAD CURRENT OPERATION

■ INTERNAL CURRENT LIMITING

■ INHIBIT FOR ZERO CURRENT

CONSUMPTION

■ SYNCHRONIZATION

■ PROTECTION AGAINST FEEDBACK

DISCONNECTION

■ THERMAL SHUTDOWN

1.1 APPLICATIONS:

■ CONSUMER: STB, DVD, TV, VCR,CAR

RADIO, LCD MONITORS

■ NETWORKING: XDSL, MODEMS,DC-DC

MODULES

■ COMPUTER: PRINTERS, AUDIO/GRAPHIC

CARDS, OPTICAL STORAGE, HARD DISK

DRIVE

■ INDUSTRIAL: CHARGERS, CAR BATTERY

DC-DC CONVERTERS

2 Description

The L5970AD is a step down monolithic power

switching regulator with a switch current limit of 1.5A

so it is able to deliver more than 1A DC current to the

load depending on the application conditions.

The output voltage can be set from 1.235V to 35V.

The device uses an internal P-Channel D-MOS tran-

sistor (with a typical R

DSON

of 200m

Ω

) as switching

element to avoid the use of bootstrap capacitor and

guarantee high efficiency.

An internal oscillator fixes the switching frequency at

500KHz to minimize the size of external components.

Having a minimum input voltage of 4.4V only, it is

particularly suitable for 5V bus, available in all com-

puter related applications.

Pulse by pulse current limit with the internal frequen-

cy modulation offers an effective constant current

short circuit protection.

1.5A SWITCH STEP DOWN SWITCHING REGULATOR

Figure 2. Test and Application Circuit

D05IN1530

L5970AD

10µF

35V

CERAMIC

330µF

10V

VOUT=3.3V

VIN = 4.4V to 35V

5.6K

3.3K

4.7K

22nF

220pF

L1 15µH

STPS2L25U

COMP

VCC

OUT

GNDINH

3.3V

SYNC.

VREF

gure 1.

age

Table 1. Order Codes

Part Number Package

L5970AD SO-8

L5970ADTR SO-8 in Tape & Reel

SO-8

Rev. 1

Summary of content (11 pages)

PAGE 1
L5970AD 1.5A SWITCH STEP DOWN SWITCHING REGULATOR 1 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ General Features Figure 1. Package 1.5A INTERNAL SWITCH OPERATING INPUT VOLTAGE FROM 4.4V TO 36V 3.3V / (±2%) REFERENCE VOLTAGE OUTPUT VOLTAGE ADJUSTABLE FROM 1.
PAGE 2
L5970AD Table 2. Thermal Data Symbol Rth (j-amb) Parameter Thermal Resistance Junction to ambient Max. Value Unit 120 (*) °C/W (*) Package mounted on board Figure 3. Pin Connection (top view) OUT 1 8 VCC SYNC 2 7 GND INH 3 6 VREF COMP 4 5 FB D98IN955 Table 3. Pin Description N. Name 1 OUT 2 SYNC Master/Slave Synchronization. When it is open, a signal synchronous with the turn-off of the internal power is present at the pin.
PAGE 3
L5970AD Table 5. Electrical Characteristics (Tj = 25°C, VCC = 12V, unless otherwise specified.) Symbol VCC RDSON Parameter Test Condition Operating input voltage range Min. Maximum limiting current fs Switching frequency Max. 36 V 0.250 0.5 Ω 4.4 Mosfet on Resistance Il Typ. VCC = 4.4V to 36V 1.8 A 500 Duty cycle 0 Unit KHz 100 % 1.25 V DYNAMIC CHARACTERISTICS V5 Voltage feedback 4.4V < VCC < 36V η Efficiency VO = 5V, VCC = 12V 1.220 1.
PAGE 4
L5970AD 3 Functional Description The main internal blocks are shown in Fig. 4, where is reported the device block diagram. They are: ● A voltage regulator that supplies the internal circuitry. From this regulator, a 3.3V reference voltage is externally available. ● A voltage monitor circuit that checks the input and internal voltages.
PAGE 5
L5970AD Figure 5. Internal Regulator Circuit VCC STARTER PREREGULATOR VREG BANDGAP IC BIAS VREF D00IN1126 3.3 OSCILLATOR & SYNCHRONIZATOR Figure 6 shows the block diagram of the oscillator circuit. The Clock Generator provides the switching frequency of the device that is internally fixed at 500KHz. The frequency shifter block acts reducing the switching frequency in case of strong overcurrent or short circuit.
PAGE 6
L5970AD 3.4 CURRENT PROTECTION The L5970AD has two current limit protections, pulse by pulse and frequency fold back. The schematic of the current limitation circuitry for the pulse by pulse protection is shown in figure 7. The output power PDMOS transistor is split in two parallel PDMOS. The smallest one has a resistor in series, RSENSE.
PAGE 7
L5970AD The turn on of the power element, or better, the rise time of the current at turn on, is a very critical parameter 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.
PAGE 8
L5970AD 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 devices turns on and off continuously 4 Additional Features and Protections 4.
PAGE 9
L5970AD 6 Package Information Figure 9. SO-8 Mechanical Data & Package Dimensions mm inch DIM. 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 D (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 ddd OUTLINE AND MECHANICAL DATA 0˚ (min.), 8˚ (max.) 0.10 0.
PAGE 10
L5970AD 7 REVISION HISTORY Table 6. Revision History 10/11 Date Revision March 2005 1 Description of Changes Initial load.
PAGE 11
L5970AD Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice.