UNISEM US3036CS Datasheet
FEATURESFEATURES
8 pin SOIC Switching Controller with
HICCUP Current Limiting Reduces Diode Power
Dissipation to Less than 1% of Normal Operation
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
APPLICATIONSAPPLICATIONS
Single input Switching Regulators such as Simple
5V to 2.5V switcher for RDRAM regulator
US3036
8 PIN PWM SWITCHER
CONTROLLER IC
PRELIMINARY DATASHEET
DESCRIPTIONDESCRIPTION
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 processors. 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 comparator for fast transient response, a precise voltage reference for setting the output voltage as well as a direct
drive of the MOSFET for the minimum part count.
TYPICAL APPLICATIONTYPICAL APPLICATION
C8
ATX
P.S.
5V
5V(S.B.)
L1
C1
5678
GndCS-CS+SS
US3036
Drv Vcc Vfb NC
1 2 3 4
R1
C2
C3
Q2
C4
R3 C5
D1R2
Typical application of US3036
C6
R7
R6
L2
Vout
C7
R4
R5
3036app2-1.0
PACKAGE ORDER INFORMATIONPACKAGE ORDER INFORMATION
TA (°C) 8 PIN PLASTIC
SOIC (S)
0 TO 70 US3036CS
Rev. 1.1
12/4/98
4-1
US3036
ABSOLUTE MAXIMUM RATINGSABSOLUTE MAXIMUM RATINGS
VCC Supply Voltage ............................................................. 20V
F.B Pin Voltage........................................................ -0.3V to 5V
Storage Temperature Range ................................. -65 TO 150°C
Operating Junction Temperature ............................... 0 TO 150°C
PACKAGE INFORMATIONPACKAGE INFORMATION
8 PIN PLASTIC SOIC (S)
TOP VIEW
1
Drv
2
Vcc
3
Vfb
4
NC Gnd
θJA =160°C/W
8
SS
7
CS+
6
CS-
5
ELECTRICAL SPECIFICATIONSELECTRICAL SPECIFICATIONS
Unless otherwise specified the following specification applies over VCC =5V, and TA =0 to 70°C. Low duty cycle
pulse testing are used which keeps junction and case temperatures equal to the ambient temperature.
PARAMETER SYM TEST CONDITION MIN TYP MAX UNITS
F.B Voltage Initial Accuracy VFB TJ =25°C 1.237 1.250 1.262 V
F.B Voltage Total Variation 1.225 1.250 1.275 V
F.B Voltage Line Regulation 0.2 %
F.B Input Bias Current IFB VFB =1.25V -1 +1 uA
Min On Time VFB is sq wave with 300 ns on 800 nS
time and 2 uS off time
Min Off Time VFB is sq wave with 300 ns off 800 nS
time and 2 uS on time
Supply Current ICCSW VFB =1.5V 10 mA
Maximum Duty Cycle DMAX VFB =1.5V 100 %
Minimum Duty Cycle DMIN VFB =1V 0 %
Gate Drive Rise/Fall Time VGATE Load=1000pF 70 nS
C.L Threshold Current ICL C.S+ , C.S- from 1.3V to 3.7V 20 uA
C.S Comp Common Mode VCS+ = VCS- 0 4.5 V
Soft Start Current 10 uA
UVLO Threshold VUVLO 4.25 4.4 4.55 V
4-2
Rev. 1.1
12/4/98
PIN DESCRIPTIONSPIN DESCRIPTIONS
PIN # PIN SYMBOL PIN DESCRIPTION
3 VFB
6 C.S-
7 C.S+
5 Gnd
1 Drv
2 VCC
8 S.S
4 N.C
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 connected 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 connected 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 current 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.
US3036
BLOCK DIAGRAMBLOCK DIAGRAM
Vcc NC
2 4 3
Drv
1
Gnd
5
Vfb
5V Reg
UVLO
PWM Control
S.S. / Hiccup
Control
R
1.25V
R
20uA
Vref
3036blk1-1.2
Figure 1 - Simplified block diagram of the US3036
CS-
6
CS+
7
SS
8
Rev. 1.1
12/4/98
4-3
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