ST ST1843, ST1845 User Manual

ST1843

ST1845

Rad-tolerant current mode PWM controller

Features

■ Oscillator frequency guaranteed at 250 kHz

■ Trimmed oscillator for precise frequency control

■ Current mode operation to 500 kHz automatic feed forward compensation

Flat-8

■ Latching PWM for cycle-by-cycle current limiting

■ Internally trimmed reference with undervoltage lockout

■ High current totem pole output

■ Undervoltage lockout with hysteresis

■ Low start-up and operating current

■ Hermetic package

■ 50 and 100 krad (Si)

■ SEL free @ 120 MeV/cm2/mg at 125°C

Description

The ST1843HR and ST1845HR ICs are radtolerant current mode PWM controllers providing an industry standard solution for the implementation of provides the off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count.

Its radiation hardness and hermetic packaging makes it an ideal choice for aerospace and other harsh environments.

Table 1.	Device summary
Order codes		Duty cycle max		Radiation level	Quality level	EPPL	Package	Lead finish	Mass (g)
ST1843K1		100%		50 krad (Si)	Engineering Model	-	Flat-8	Gold	0.45
ST1843FKG		100%		50 krad (Si)	According to ESCC	Target	Flat-8	Gold	0.45
ST1845K1		50%		100 krad (Si)	Engineering Model	-	Flat-8	Gold	0.45
ST1845RKG		50%		100 krad (Si)	According to ESCC	Target	Flat-8	Gold	0.45

September 2011

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Contents	ST1843 - ST1845

Contents

1	Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		3
2	Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		4
3	Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		4
4	Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5
5	Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		6
6	Radiation characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		9
	6.1	Total dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9

6.1.1 Bias conditions and total dose level for total dose radiation testing . . . . . 9 6.1.2 Electrical measurements for total dose radiation testing . . . . . . . . . . . . 10 6.1.3 Heavy Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7	Test circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
8	Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22
9	Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
10	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24

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ST1843 - ST1845	Block diagram

1 Block diagram

Figure 1. Block diagram (toggle flip flop used only in UC3844B and UC3845B)

9L
	9	89/2		9
						95()
			6 5
*5281'				5()		9 P$
				,17(51$/
		9			%,$6
				95() *22'
				/2*,&		287387
57 &7		26&		7
		(5525$03		6
		5
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		5		9	/$7&+
&203				&855(17
				6(16(
&855(17				&203$5$725
6(16(
						!-V

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Maximum ratings				ST1843 - ST1845
2	Maximum ratings
	Table 2.	Absolute maximum ratings
	Symbol	Parameter		Value	Unit
	Vi	Supply voltage (low impedance source)	30		V
		Supply voltage (Ii < 30mA)		Self limiting
	IO	Output current	±1		A
	EO	Output energy (capacitive load)	5		mJ
		Analog inputs (pins 2, 3)		– 0.3 to 5.5	V
		Error amplifier output sink current	10		mA
	Ptot	Power dissipation at TA ≤ 25 °C (SO8)	800		mW
	Tstg	Storage temperature range		– 65 to 150	°C
	TJ	Junction operating temperature		– 40 to 150	°C
Note:	All voltages are with respect to pin 5, all currents are positive into the specified terminal.
3	Thermal data
	Table 3.	Thermal data
	Symbol	Description		Flat-8	Unit
	RthJA	Thermal resistance Junction-ambient. max.		100	°C/W

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ST1843 - ST1845	Pin connection

4 Pin connection

Figure 2.		Pin connection
				',3 62
			&203			95()
			9)%			9L
			,6(16(			287387
			57&7			*5281'
						!-V
Table 4.		Pin functions
No	Function				Description
1	COMP		This pin is the error amplifier output and is made available for loop compensation.
2	VFB		This is the inverting input of the error amplifier. It is normally connected to the
			switching power supply output through a resistor divider.
3	ISENSE		A voltage proportional to inductor current is connected to this input. The PWM uses
			this information to terminate the output switch conduction.
			The oscillator frequency and maximum output duty cycle are programmed by
4	RT/CT		connecting resistor RT to Vref and capacitor CT to ground. Operation to 500 kHz is
			possible.
5	GROUND		This pin is the combined control circuitry and power ground.
6	OUTPUT		This output directly drives the gate of a power MOSFET. Peak currents up to 1A are
			sourced and sunk by this pin.
7	VCC		This pin is the positive supply of the control IC.
8	Vref		This is the reference output. It provides charging current for capacitor CT through
			resistor RT.

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Electrical characteristics	ST1843 - ST1845

5 Electrical characteristics

Maximum package power dissipation limits must be respected; low duty cycle pulse techniques are used during test maintain TJ as close to TA as possible.

Unless otherwise stated, these specifications apply for - TA = 22 ±3°C, Vi = 15 V, Adjust Vi above the start threshold before setting at 15 V; RT = 10 kΩ; CT = 3.3 nF.

Table 5.	Electrical characteristics
	MIL-STD-								Values
Symbol	883 test	Parameter			Test conditions						Unit
									Min.	Max.
	method
Reference section
			V	= 15V	(1); R	= 10kΩ; C	T	= 3.3nF,
VREF		Output voltage	I		T				4.95	5.05	V
			Io = 1mA
VREF_LINE		Line regulation	12V ≤ Vi		≤ 25V, RT = 10kΩ; CT =					0.02	V
			3.3nF
VREF_LOAD		Load regulation	VI	= 15V (1); RT = 10kΩ; CT = 3.3nF,						25	V
ISC	3011	Output short circuit	1 ≤ Io ≤ 20mA						-0.18	-0.03	A
Oscillator section
fOSC		Frequency for ST1843	VI = 15V (1); RT = 10kΩ; CT = 3.3nF,						49	55	kHz
		Frequency for ST1845	1 ≤ Io ≤ 20mA						24.5	27.5	kHz
fOSC/ V		Frequency change with	12V ≤ VI		≤ 25V; RT = 10kΩ; CT =				–	1	%
		voltage	3.3nF
Idischg		Discharge current	VI = 15V (1); RT = 10kΩ; CT = 3.3nF,						7.8	8.8	mA
			1 ≤ Io ≤ 20mA, VOSC = 2V						7.5	8.8	mA
Error amp section
			V	= 15V	(1); R	= 10kΩ; C	T	= 3.3nF,
V2		Input voltage	I		T				2.45	2.55	V
			VPIN1 = 2.5V
			V	= 15V	(1); R	= 10kΩ; C	T	= 3.3nF,
Ib	4001	Input bias current	I		T				-1		mA
			VFB = 5V
			V	= 15V	(1); R	= 10kΩ; C	T	= 3.3nF,
AVOL		AVOL	I		T				65		dB
			2V ≤ Vo ≤ 4V
PSRR	4003	Power supply rejec. ratio	12V ≤ Vi ≤ 25V; RT = 10kΩ; CT =						60		dB
			3.3nF
			V	= 15V	(1); R	= 10kΩ; C = 3.3nF,
Io_sink		Output sink current	I		T		T		2		mA
			VPIN2 = 2.7V, VPIN1 = 1.1V
			V	= 15V	(1); R	= 10kΩ; C	T	= 3.3nF,
Io_source		Output source current	I		T					-0.5	mA
			VPIN2 = 2.2V, VPIN1 = 5V

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ST1843 - ST1845

Electrical characteristics

Table 5.

Electrical characteristics (continued)

MIL-STD-

Values

Symbol

883 test

Parameter

Test conditions

Unit

Min.

Max.

method

V

= 15V

(1); R

= 10kΩ; C

= 3.3nF,

VOH

VOUT high

I

T

T

5

V

VPIN2 = 2.3V, RL = 15kΩ to GND

V

= 15V

(1); R

= 10kΩ; C

= 3.3nF,

VOL

VOUT low

I

T

T

1.1

V

VPIN2 = 2.3V, RL = 15kΩ to GND

Current sense section

V

= 15V

(1); R

= 10kΩ; C

= 3.3nF,

GV

4004

Gain

I

T

T

2.85

3.15

V/V

(2) (3)

V

= 15V

(1); R

= 10kΩ; C

= 3.3nF,

V3

Maximum input signal

I

T

T

0.9

1.1

V

VPIN1 = 2.3V

(2)

SVR

Supply voltage rejection

12 ≤ Vi ≤ 25V; RT = 10kΩ;

60

dB

C

= 3.3nF,(1)

T

I

4001

Input bias current

V

= 15V

(1); R

= 10kΩ; C

T

= 3.3nF

-10

mA

b

I

T

D

3003

Delay to output

V = 15V

(1); R

= 10kΩ; C

T

= 3.3nF

300

ns

O

I

T

Output section

V

= 15V

(1); R

= 10kΩ; C

= 3.3nF;

VOL1

I

T

T

0.4

V

ISINK = 20mA

3007

Output low level

V

= 15V

(1); R

= 10kΩ; C

= 3.3nF;

VOL2

I

T

T

2.2

V

ISINK = 200mA

V

= 15V

(1); R

= 10kΩ; C

= 3.3nF;

VOH1

I

T

T

13

V

ISOURCE

= 20mA

3006

Output high level

V

= 15V

(1); R

= 10kΩ; C

= 3.3nF;

VOH2

I

T

T

12

V

ISOURCE

= 200mA

V

= 6V (1); R = 10kΩ; C

= 3.3nF;

VOLS

UVLO saturation

I

T

T

1.1

V

ISINK = 1mA

tr

Rise time

VI

= 15V

(1)

= 10kΩ; CT = 3.3nF;

150

ns

3004

; RT

tf

Fall time

CL = 1nF

150

ns

Under-voltage lockout section

V

TH

Start threshold

V

= 15V

(1); R

= 10kΩ; C

T

= 3.3nF

7.8

9

V

I

T

V

MIN

Min operating voltage after

V

= 15V

(1); R

= 10kΩ; C

T

= 3.3nF

7

8.2

V

turn-on

I

T

DC

Max duty cycle for ST1843

V

= 15V

(1); R

= 10kΩ; C

= 3.3nF

47

50

%

T

MAX

Max duty cycle for ST1845

I

T

94

100

%

DC

Min duty cycle

V = 15V

(1); R

= 10kΩ; C

T

= 3.3nF

0

%

MIN

I

T

Total standby current

I

st

Start-up current

V

= 15V

(1); R

= 10kΩ; C

T

= 3.3nF

0.5

mA

I

T

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Electrical characteristics

ST1843 - ST1845

Table 5.

Electrical characteristics (continued)

MIL-STD-

Values

Symbol

883 test

Parameter

Test conditions

Unit

Min.

Max.

method

V

I

= 15V

(1); R

= 10kΩ; C

T

= 3.3nF

Ii

3005

Operating supply current

T

17

mA

VPIN2 = VPIN3 = 0V

V

I

= 15V

(1); R

= 10kΩ; C

T

= 3.3nF

Viz

Zener voltage

T

30

V

Ii = 25mA

1.Adjust Vi above the start threshold before setting at 15V

2.Parameter measured at trip point of latch with VPIN2 = 0.

3. Gain defined as:	VPIN1	≤ VPIN3	≤ 0.8V
A =	-------------------;0
	VPIN3

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