US3036

4-1

Rev. 1.1
12/4/98

8 PIN PWM SWITCHER

CONTROLLER IC

Typical application of US3036

TA (°C) 8 PIN PLASTIC

SOIC (S)
0 TO 70 US3036CS

DESCRIPTION

The US3036 IC provides an 8 pin low cost switching
controller with true short circuit protection all in a
compact 8 pin surface mount package, providing a
low cost switching solution for applications that re-
quire a simple switching regulator from the 5V input where
there is no other supply available. One type of such
application is generating 2.5V standby from the dual
5V(5V and 5V standby) for the next generation proces-
sors. The IC starts below 4.5V supply and drives an
external Pch MOSFET or and external low cost PNP as
the switching element. The IC also includes an error com-
parator for fast transient response, a precise voltage ref-
erence for setting the output voltage as well as a direct
drive of the MOSFET for the minimum part count.

FEATURES

8 pin SOIC Switching Controller with
HICCUP Current Limiting Reduces Diode Power
Dissipation to Less than 1% of Normal Opera-
tion
Soft Start Capacitor allows for smooth Output
Voltage ramp up
On board MOSFET driver
Fastest transient response of any controller
method. ( 0 to 100% Duty Cycle in 100 nS )
1% internal voltage reference
Internal Under Voltage Lockout protects
MOSFET during start-up

APPLICATIONS

Single input Switching Regulators such as Simple
5V to 2.5V switcher for RDRAM regulator

PACKAGE ORDER INFORMATION

PRELIMINARY DATASHEET

TYPICAL APPLICATION

3036app2-1.0

Vout

US3036

2 3

Drv Vcc

Vfb

Gnd

CS-

CS+

ATX
P.S.

5V(S.B.)

US3036

4-2

Rev. 1.1

12/4/98

ABSOLUTE MAXIMUM RATINGS

Supply Voltage ............................................................. 20V

F.B Pin Voltage........................................................ -0.3V to 5V
Storage Temperature Range ................................. -65 TO 150

Operating Junction Temperature ............................... 0 TO 150

PACKAGE INFORMATION

8 PIN PLASTIC SOIC (S)

=160

C/W

PARAMETER

SYM TEST CONDITION

MIN TYP MAX UNITS

F.B Voltage Initial Accuracy

=25

1.237

1.250

1.262

F.B Voltage Total Variation

1.225

1.250

1.275

F.B Voltage Line Regulation

0.2

F.B Input Bias Current

=1.25V

-1

Min On Time

is sq wave with 300 ns on

800

time and 2 uS off time

Min Off Time

is sq wave with 300 ns off

800

time and 2 uS on time

Supply Current

CCSW

=1.5V

Maximum Duty Cycle

MAX

=1.5V

100

Minimum Duty Cycle

MIN

=1V

Gate Drive Rise/Fall Time

GATE

Load=1000pF

C.L Threshold Current

C.S+ , C.S- from 1.3V to 3.7V

C.S Comp Common Mode

CS+

= V

CS-

4.5

Soft Start Current

UVLO Threshold

UVLO

4.25

4.4

4.55

ELECTRICAL SPECIFICATIONS

Unless otherwise specified the following specification applies over V

=5V, and T

=0 to 70

C. Low duty cycle

pulse testing are used which keeps junction and case temperatures equal to the ambient temperature.

TOP VIEW

Drv

Vcc

Vfb

Gnd

CS-

CS+

US3036

4-3

Rev. 1.1
12/4/98

PIN DESCRIPTIONS

PIN # PIN SYMBOL

PIN DESCRIPTION

BLOCK DIAGRAM

Figure 1 - Simplified block diagram of the US3036

A resistor divider from this pin to the output of the switching regulator and ground sets the
Core supply voltage.
This pin is connected to the minus side of the external current sense resistor. An internal
current source together with an external resistor in series with this pin programs the
current limit threshold voltage. This voltage divided by the external current sense resistor
sets the current limit threshold.
This pin is connected to the plus side of the external current sense resistor. A resistor in
series with this pin and a capacitor connected between this pin and pin 6 provides a high
frequency filtering for the noise spikes of turn on and turn off switching.
This pin is connected to the IC substrate and must be connected to the lowest potential
in the system.
The PWM output of the switching controller. This pin is a totem pole drive that is con-
nected to the gate of the power MOSFET. A resistor may be placed from this pin to the
gate in order to reduce switching noise.
This pin supplies the voltage to the PWM drive and hysterises circuitry and it is con-
nected to the same supply as the input supply to the switching regulator . A 1 uF, high
frequency capacitor must be connected from this pin to ground to provide the peak cur-
rent for charging and discharging of the MOSFET.
This pin provides the soft start for the regulator during power up. It also sets a long off
time when the converter goes into current limiting, providing low duty cycle for the catch
diode allowing it to survive during short circuit.
No connect.

C.S-

C.S+

Gnd

1 Drv

S.S

N.C

Vref

UVLO

1.25V

PWM Control

Vcc

CS+

Drv

Gnd

Vfb

CS-

3036blk1-1.2

5V Reg

S.S. / Hiccup

Control

20uA

US3036

4-4

Rev. 1.1

12/4/98

Figure 2- The circuit in figure 2 is the application of the US3036 providing a low cost solution for a 2.5V/2A supply from

the 5V dual supply. This circuit uses current sense resistor to set the current limiting.

TYPICAL APPLICATION

5V to 2.5V for RDRAM Supply

Ref Desig

Description Qty

Part #

Manufacturer

LDO/Switcher IC

US3036CS ( 8 pin SOIC)

Unisem

MOSFET

IRF7204 (8 pin SOIC) or IRF7406 for 4A

P Ch

SI9435DY (8 pin SOIC) or SI4431 for 4A Temic

Schottky Diode

SK33DICT (SMC)

Lite on

Inductor

Core:T44-52,L=6 uH

Micro Metal

Turns: 15T, 20 AWG

(core)

Inductor

L=1 uH

Resistor

10 ohm,5%, SMT 1206 size

Resistor

10 ohm, 5%, SMT 1206 size

Resistor

200 kohm,1%, SMT 0805 size

Resistor

1 kohm,1%, SMT 0805 size

Resistor

1 kohm,1%, SMT 0805 size

Resistor

5 miliohm,5%, 2W

Ohmite

R7,8

Resistor

3.57 kohm,1%, SMT 0805 size

Capacitor

470uF,10V, Elect

Sanyo

Capacitor

10CV1000DX, 1000uF,10V, Elect ,ESR=0.07 Ohm

Sanyo

Capacitor

1 uF,Ceramic, SMT 0805 size

Capacitor

470 pF,Ceramic, SMT 0805 size

Sanyo

Capacitor

10 pF,Ceramic, SMT 0805 size

Sanyo

Capacitor

4700pF

Capacitor

10CV1000DX, 1000uF,10V, Elect ,ESR=0.07 Ohm

Sanyo

Capacitor

0.15 uF

3036app1-1.3

Vout

US3036

2 3

Drv Vcc

Vfb

Gnd

CS-

CS+

ATX
P.S.

5V(S.B.)

US3036

4-5

Rev. 1.1
12/4/98

Figure 2- The circuit in figure 2 is the application of the US3036 providing a low cost solution for a 2.5V supply from

the 5V dual supply.

TYPICAL APPLICATION

5V to 2.5V for RDRAM Supply

3036app2-1.0

Vout

US3036

Drv Vcc

Vfb

Gnd

CS-

CS+

ATX
P.S.

5V(S.B.)

Ref Desig

Description Qty

Part #

Manufacturer

LDO/Switcher IC

US3036CS ( 8 pin SOIC)

Unisem

MOSFET

IRF7204 (8 pin SOIC) or IRF7406 for 4A

P Ch

SI9435DY (8 pin SOIC) or SI4431 for 4A Temic

Schottky Diode

SK33DICT (SMC)

Lite on

Inductor

Core:T44-52,L=6 uH

Micro Metal

Turns: 15T, 20 AWG

(core)

Inductor

L=1 uH

Resistor

10 ohm,5%, SMT 1206 size

Resistor

10 ohm, 5%, SMT 1206 size

Resistor

200 kohm,1%, SMT 0805 size

Resistor

1 kohm,1%, SMT 0805 size

Resistor

1 kohm,1%, SMT 0805 size

Resistor

1 kohm,5%

Resistor

3.57 kohm,1%, SMT 0805 size

Capacitor

470uF,10V, Elect

Sanyo

Capacitor

10CV1000DX, 1000uF,10V, Elect ,ESR=0.07 Ohm

Sanyo

Capacitor

1 uF,Ceramic, SMT 0805 size

Capacitor

470 pF,Ceramic, SMT 0805 size

Sanyo

Capacitor

10 pF,Ceramic, SMT 0805 size

Sanyo

Capacitor

0.1uF

Capacitor

10CV1000DX, 1000uF,10V, Elect ,ESR=0.07 Ohm

Sanyo

Capacitor

0.15 uF

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