Microlinear ML4825 Technical data

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May 1997

ML4825*

High Frequency Power Supply Controller

GENERAL DESCRIPTION

The ML4825 High Frequency PWM Controller is an IC
controller optimized for use in Switch Mode Power
Supply designs running at frequencies to 1MHz.
Propagation delays are minimal through the comparators
and logic for reliable high frequency operation while slew
rate and bandwidth are maximized on the error amplifier.
This controller is designed to work in either voltage or
current mode and provides for input voltage feed forward.

FEATURES

■ Practical operation at switching frequencies to 1.0MHz

■ High current (2A peak) dual totem pole outputs

■ Wide bandwidth error amplifier

■ Fully latched logic with double pulse suppression

■ Pulse-by-pulse current limiting

■ Soft start and maximum duty cycle control

■ Under voltage lockout with hysteresis

A 1V threshold current limit comparator provides cycle­by-cycle current limit while exceeding a 1.4V threshold
initiates a soft-start cycle. The soft start pin doubles as a
maximum duty cycle clamp. An under-voltage lockout
circuit with 800mV of hysteresis assures low startup
current and drives the outputs low.

This controller is similar in architecture and performance
to the UC1825 controller, however the ML4825 includes
many features not found on the 1825. These features are
set in

Italics

.

■ Precision trimmed 5.1V bandgap reference

■ Pin compatible improved replacement for UC1825

■

Fast shut down path from current limit to outputs

■

Outputs preset to known condition after under voltage
lockout

■

Soft start latch ensures full soft start cycle

■

Outputs pull low for undervotage lockout

BLOCK DIAGRAM (Pin configuration shown for 16-pin version) *Some Packages Are Obsolete or End Of Life

R

T

5

C

T

6

OSC

CLOCK OUT

4

RAMP

7

E/A OUT

3

NI

2

INV

1

SS

8

I

LIM

9

/SD

1V

1.4V

1.25V

+

ERROR

AMP

+

–

–
+

+
–

9µA

COMP

+

–

C

V+

R

S

Q

TF.F.

Q

P

–
+

1V

Q

UNDER

VOLTAGE

LOCKOUT

R

S

Q

PWR V

C

13

OUT A

11

POWER GND

POWER V

ENABLE

V

REF

9V

–
+

V

REF

GEN

INTERNAL

BIAS

C

PWR GND

+

4V

–

1.5V V

SIGNAL GND

OUT B

REF

V

CC

14

12

16

15

10

1

ML4825

PIN CONFIGURATION

ML4825

16-Pin PDIP

ML4825

20-Pin PLCC

16-Pin SOIC

INV

E/A OUT

CLOCK

RAMP

1

NI

2

3

4

R

5

T

C

6

T

7

SS

8

TOP VIEW

16

15

14

13

12

11

10

9

5.1V REF

V

CC

OUT B

V

C

PWR GND

OUT A

GND

I

/SD

LIM

E/A OUT

CLOCK

NC

R

C

NI

INVNC5.1V REF

3212019

4

5

6

7

T

8

T

910111213

SS

RAMP

TOP VIEW

PIN DESCRIPTION (Pin number in parentheses is for PLCC version)

PIN NAME FUNCTION PIN NAME FUNCTION

1 (2) INV Inverting input to error amp.

2 (3) NI Non-inverting input to error amp.

3 (4) E/A OUT Output of error amplifier and input

to main comparator

4 (5) CLOCK Oscillator output

9 (12) I

/SD Current limit sense pin. Normally

LIM

connected to current sense resistor.

10 (13) GND Analog signal ground

11 (14) OUT A High current totem pole output. This

output is the first one energized after
power on reset

NC

/SD

LIM

I

CC

V

18

17

16

15

14

GND

OUT B

V

C

NC

PWR GND

OUT A

5 (7) R

T

Timing resistor for oscillator—
sets charging current for oscillator
timing capacitor (pin 6)

6 (8) C

T

Timing capacitor for oscillator

7 (9) RAMP Non-inverting input to main

comparator. Connected to CT for
voltage mode operation or to current
sense resistor for current mode

8 (10) SS Normally connected to soft start

capacitor

12 (15) PWR GND Return for the high current totem

pole outputs

13 (17) V

C

Positive supply for the high current
totem pole output

14 (18) OUT B High current totem pole output

15 (19) V

CC

Positive supply for the IC

16 (20) 5.1V REF Buffered output for the 5.1V voltage

reference

2

ABSOLUTE MAXIMUM RATINGS

ML4825

Absolute maximum ratings are those values beyond which
the device could be permanently damaged. Absolute
maximum ratings are stress ratings only and functional
device operation is not implied.

Supply Voltage (V

) ........................................... 30V

C, VCC

Output Current, Source or Sink (OUT A, OUT B)

Junction Temperature

ML4825IX, ML4825CX ....................................... 150°C

Storage Temperature Range ..................... –65°C to 150°C

Lead Temperature (soldering 10 sec.) ..................... 260°C

Thermal Resistance (θ

)

JA

Plastic DIP or SOIC ......................................... 65°C/W

Plastic Chip Carrier (PCC) ................................ 60°C/W

DC ....................................................................... 0.5A

Pulse (0.5µs) ......................................................... 2.0A

Analog Inputs

OPERATING CONDITIONS

(INV, NI, RAMP)................................ GND –0.3V to 7V

(SS, I

CLOCK Output Current ...........................................–5mA

E/A OUT Output Current .......................................... 5mA

Soft Start Sink Current ............................................ 20mA

) ........................................... GND –0.3V to 6V

LIM

Temperature Range

ML4825CX ................................................ 0°C to 70°C

ML4825IX .............................................. –40°C to 85°C

RT Charging Current ................................................–5mA

ELECTRICAL CHARACTERISTICS

Unless otherwise specified, R

PARAMETER CONDITIONS MIN TYP MAX UNITS

OSCILLATOR

Initial Accuracy T

Voltage Stability 10V < VCC < 30V, T

Temperature Stability 5%

Total Variation Line, temperature 340 460 kHz

Clock Out High 3.9 4.5 V

Clock Out Low 2.3 2.9 V

Ramp Peak 2.6 2.8 3.0 V

Ramp Valley 0.7 1.0 1.25 V

Ramp Valley to Peak 1.6 1.8 2.0 V

REFERENCE

Output Voltage T

Line Regulation 10V < VCC < 30V –20 2 20 mV

Load Regulation 1mA < IO < 10mA –20 5 20 mV

Temperature Stability –55°C < TJ < 150°C 0.2 0.4 %

Total Variation Line, load, temperature C suffix 4.95 5.25 V

Output Noise Voltage 10Hz to 10kHz 50 µV

Long Term Stability T

Short Circuit Current V

ERROR AMPLIFIER

Input Offset Voltage C suffix –15 15 mV

Input Bias Current 0.6 3 µA
Input Offset Current 0.1 1 µA

Open Loop Gain 1 < VO < 4V 60 96 dB

= 3.65kΩ, C

T

= 1000pF, TA = Operating Temperature Range, VCC = 15V (Note 1).

T

= 25°C 360 400 440 kHz

J

= 25°C –2 0.2 2 %

A

= 25°C, I

J

= 125°C, 1000 hours 5 25 mV

J

= 0V –15 –50 –100 mA

REF

I suffix –15 15 mV

= 1mA C suffix 5.00 5.10 5.20 V

O

I suffix 5.00 5.10 5.20 V

I suffix 4.95 5.25 V

3