ST L4962 User Manual

®

L4962

1.5A POWER SWITCHING REGULATOR

1.5A OUTPUT CURRENT
5.1V TO 40V OUTPUT VOLTAGE RANGE
PRECISE (± 2%) ON-CHIP REFERENCE
HIGH SWITCHING FREQUENCY
VERY HIGH EFFICIENCY (UP TO 90%)
VERY FEW EXTERNAL COMPONENTS	POWERDIP	HEPTAWATT
SOFT START	(12 + 2 + 2)
INTERNAL LIMITING CURRENT	ORDERING NUMBERS : L4962/A (12 + 2 + 2 Powerdip)
THERMAL SHUTDOWN		L4962E/A (Heptawatt
		Vertical)
		L4962EH/A (Horizontal
		Heptawatt)
DESCRIPTION

The L4962 is a monolithic power switching regulator delivering 1.5A at a voltage variable from 5V to 40V in step down configuration.

Features of the device include current limiting, soft start, thermal protection and 0 to 100% duty cycle for continuous operating mode.

The L4962 is mounted in a 16-lead Powerdip plastic package and Heptawatt package and requires very few external components.

Efficient operation at switching frequencies up to 150KHz allows a reduction in the size and cost of external filter components.

BLOCK DIAGRAM

Pin X = Powerdip

Pin (X) = Heptawatt

June 2000

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L4962

ABSOLUTE MAXIMUM RATINGS

	Symbol	Parameter	Value	Unit
	V7	Input voltage	50	V
	V7 - V2	Input to output voltage difference	50	V
	V2	Negative output DC voltage	-1	V
		Output peak voltage at t = 0.1μs; f = 100KHz	-5	V
	V11, V15	Voltage at pin 11, 15	5.5	V
	V10	Voltage at pin 10	7	V
	I11	Pin 11 sink current	1	mA
	I14	Pin 14 source current	20	mA
	Ptot	Power dissipation at Tpins ≤ 90°C (Powerdip)	4.3	W
		Tcase ≤ 90°C (Heptawatt)	15	W
	Tj, Tstg	Junction and storage temperature	-40 to 150	°C

PIN CONNECTION (Top view)

THERMAL DATA

Symbol	Parameter		Heptawatt	Powerdip
Rth j-case	Thermal resistance junction-case	max	4°C/W	-
Rth j-pins	Thermal resistance junction-pins	max	-	14°C/W
Rth j-amb	Thermal resistance junction-ambient	max	50°C/W	80°C/W*

* Obtained with the GND pins soldered to printed circuit with minimized copper area.

PIN FUNCTIONS

HEPTAWATT	POWERDIP	NAME	FUNCTION
1	7	SUPPLY VOLTAGE	Unregulated voltage input. An internal regulator powers
			the internal logic.
2	10	FEEDBACK INPUT	The feedback terminal of the regulation loop. The output
			is connected directly to this terminal for 5.1V operation;
			it is connected via a divider for higher voltages.
3	11	FREQUENCY	A series RC network connected between this terminal
		COMPENSATION	and ground determines the regulation loop gain
			characteristics.

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				L4962
PIN FUNCTIONS (cont’d)
	HEPTAWATT	POWERDIP	NAME	FUNCTION
4		4, 5, 12, 13	GROUND	Common ground terminal.
5		14	OSCILLATOR	A parallel RC network connected to this terminal
				determines the switching frequency. This pin must be
				connected to pin 7 input when the internal oscillator is
				used.
6		15	SOFT START	Soft start time constant. A capacitor is connected
				between this terminal and ground to define the soft start
				time constant. This capacitor also determines the
				average short circuit output current.
7		2	OUTPUT	Regulator output.
		1, 3, 6,		N.C.
		8, 9, 16

ELECTRICAL CHARACTERISTICS (Refer to the test circuit, Tj = 25 °C, Vi = 35V, unless otherwise specified)

Symbol	Parameter	Test Conditions	Min.	Typ.	Max.	Unit

DYNAMIC CHARACTERISTICS

Vo	Output voltage range	Vi = 46V			Io = 1A	Vref		40	V
Vi	Input voltage range	Vo = Vref to 36V			Io = 1.5A	9		46	V
Vo	Line regulation	Vi = 10V to 40V		Vo = Vref Io = 1A			15	50	mV
Vo	Load regulation	Vo = Vref			Io = 0.5A to 1.5A		8	20	mV
Vref	Internal reference voltage	Vi = 9V to 46V			Io = 1A	5	5.1	5.2	V
	(pin 10)
Vref	Average temperature	Tj = 0°C to 125°C					0.4		mV/°C
T	coefficient of refer. voltage	Io = 1A
Vd	Dropout voltage	Io = 1.5A					1.5	2	V
Iom	Maximum operating load	Vi = 9V to 46V				1.5			A
	current	Vo = Vref to 36V
I2L	Current limiting threshold	Vi = 9V to 46V				2		3.3	A
	(pin 2)	Vo = Vref to 36V
ISH	Input average current	Vi = 46V;	output short-circuit				15	30	mA
η	Efficiency	f = 100KHz			Vo = Vref		70		%
		Io = 1A
					Vo = 12V		80		%
SVR	Supply voltage ripple	Vi = 2Vrms				50	56		dB
	rejection	fripple = 100Hz
		Vo = Vref			Io = 1A
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L4962

ELECTRICAL CHARACTERISTICS (continued)

Symbol	Parameter	Test Conditions	Min.	Typ.	Max.	Unit

DYNAMIC CHARACTERISTICS (cont’d)

f

Switching frequency

85

100

115

KHz

f

Voltage stability of

Vi = 9V to 46V

0.5

%

Vi

switching frequency

f

Temperature stability of

Tj = 0

°

°

1

%

C to 125 C

Tj

switching frequency

fmax

Maximum operating

Vo = Vref

Io = 1A

120

150

KHz

switching frequency

Tsd

Thermal shutdown

150

°C

junction temperature

DC CHARACTERISTICS

I7Q	Quiescent drain current	100% duty cycle			30	40	mA
		pins 2 and 14 open	Vi = 46V
		0% duty cycle			15	20	mA
-I2L	Output leakage current	0% duty cycle				1	mA

SOFT START

I15SO	Source current		100	140	180	μA
I15SI	Sink current		50	70	120	μA

ERROR AMPLIFIER

V11H	High level output voltage	V10 = 4.7V	I11 = 100μA	3.5			V
V11L	Low level output voltage	V10 = 5.3V	I11 = 100μA			0.5	V
I11SI	Sink output current	V10 = 5.3V		100	150		μA
-I11SO	Source output current	V10 = 4.7V		100	150		μA
I10	Input bias current	V10 = 5.2V			2	10	μA
Gv	DC open loop gain	V11 = 1V to 3V		46	55		dB

OSCILLATOR

-I14	Oscillator source current		5			mA

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L4962

CIRCUIT OPERATION (refer to the block diagram)

The L4962 is a monolithic stepdown switching regulator providing output voltages from 5.1V to 40V and delivering 1.5A.

The regulation loop consists of a sawtooth oscillator, error amplifier, comparator and the output stage. An error signal is produced by comparing the output voltage with a precise 5.1V on-chip reference (zener zap trimmed to ± 2%).

This error signal is then compared with the sawtooth signal to generate the fixed frequency pulse width modulated pulses which drive the output stage.

The gain and frequency stability of the loop can be adjusted by an external RC network connected to pin 11. Closing the loop directly gives an output voltage of 5.1V. Higher voltages are obtained by inserting a voltage divider.

Output overcurrents at switch on are prevented by the soft start function. The error amplifier output is initially clamped by the external capacitor Css and

Figure 1. Soft start waveforms

allowed to rise, linearly, as this capacitor is charged by a constant current source. Output overload protection is provided in the form of a current limiter. The load current is sensed by an internal metal resistor connected to a comparator. When the load current exceeds a preset threshold this comparator sets a flip flop which disables the output stage and discharges the soft start capacitor. A second comparator resets the flip flop when the voltage across the soft start capacitor has fallen to 0.4V.

The output stage is thus re-enabled and the output voltage rises under control of the soft start network. If the overload condition is still present the limiter will trigger again when the threshold current is reached. The average short circuit current is limited to a safe value by the dead time introduced by the soft start network. The thermal overload circuit disables circuit operation when the junction temperature reaches about 150°C and has hysteresis to prevent unstable conditions.

Figure 2. Current limiter waveforms

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