RT9185

DS9185-02 July 2003

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Triple, Ultra-Fast CMOS LDO Regulator

General Description

The RT9185 series are an efficient, precise triple-
channel CMOS LDO regulator specifically designed
for mother-board application. The device is intended
to powering the standby voltage in which 3.3V_PCI,
2.5V_Clock and 1.8V_ICH2 or 1.5V_ICH4 core
voltage of the PC based computer system.
Moreover, it is also optimized for CD/DVD-ROM,
CD/RW, XDSL Router or IA equipments applications.
The regulator outputs are capable of sourcing 1.5A,
0.8A and 0.3A of output current respectively.

The RT9185 also works with low-ESR ceramic
capacitors, reducing the amount of board space
necessary for power applications. The other features
include faster transient response, low dropout voltage,
high output accuracy, current limiting and thermal
shutdown protections.

The RT9185 regulators are available in fused SOP-8,
5-lead TO-252 and 5-lead TO-263 packages.

Ordering Information

RT9185

Features

Fixed Output Voltages: 3.35V at 1.5A, 2.55V at

0.8A and 1.5V or 1.8V at 0.3A

Low Quiescent Current (Typically 0.4mA)

Operating Voltage Ranges: 3.5V~5.5V

Ultra-Fast Transient Response

Tight Load and Line Regulation

Current Limiting Protection

Thermal Shutdown Protection

Only low-ESR Ceramic Capacitors Required

for Stability

Custom Voltage Available

Applications

Mother-board Power Supply

CD/DVD-ROM, CD/RW

XDSL Router

IA Equipments

Cable Modems

Pin Configurations

Part Number

Pin Configurations

RT9185 CS
(Plastic SOP-8)

RT9185 CL5
(Plastic TO-252-5)

TOP VIEW
1. VOUT1
2. VDD
3. GND (TAB)
4. VOUT2

5. VOUT3

RT9185 CM5
(Plastic TO-263-5)

TOP VIEW
1. VOUT1
2. VDD
3. GND (TAB)
4. VOUT2
5. VOUT3

1 2 3 4 5

Package Type
S : SOP-8
L5 : TO-252-5
M5 : TO-263-5

VOUT3
A : 1.8V
B : 1.5V

Operating Temperature Range
C: Commercial Standard

Other voltage versions please
contact RichTek for detail.

GND

VOUT1

VDD

VOUT2

VOUT3

GND

VOUT1

VDD

VOUT2

VOUT3

1 2 3 4 5

RT9185

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DS9185-02 July 2003

Typical Application Circuit

Pin Description

Pin Name

Pin Function

VOUT1

Channel 1 Output Voltage

VDD Supply

Input

GND Common

Ground

VOUT2

Channel 2 Output Voltage

VOUT3

Channel 3 Output Voltage

Function Block Diagram

Thermal

Sensor

Ref erence

Error Amp

VDD

VOUT1

VOUT2

VOUT3

GND

Current
Limiting

Error Amp

Current
Limiting

VDD

Thermal

Sensor

Ref erence

Error Amp

_
+

VDD

VOUT1

VOUT2

VOUT3

GND

Current
Limiting

Error Amp

Current
Limiting

VDD

GND

OUT1

(3.35V / 1.5A)

C2
4.7

�F

(5VSB)

C1
2.2

�F

OUT3

(1.5V or 1.8V / 0.3A)

OUT2

(2.55V / 0.8A)

C4
1

�F

C3
4.7

�F

VOUT1

VOUT2

RT9185

VOUT3

VDD

GND

OUT1

(3.35V / 1.5A)

C2
4.7

�F

(5VSB)

C1
2.2

�F

OUT3

(1.5V or 1.8V / 0.3A)

OUT2

(2.55V / 0.8A)

C4
1

�F

C3
4.7

�F

VOUT1

VOUT2

RT9185

VOUT3

VDD

RT9185

DS9185-02 July 2003

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Absolute Maximum Ratings

(Note 1)

Supply Input Voltage

Package Thermal Resistance

SOP-8

20�C/W

TO-252-5

10�C/W

TO-263-5,

5.5�C/W

Lead Temperature (Soldering, 10 sec.)

260

�C

Junction Temperature

150

�C

Storage Temperature Range

-65�C to 150�C

ESD Susceptibility (Note 2)

HBM 2kV

MM 200V

Recommended Operating Conditions

(Note 3)

Supply Input Voltage

3.5V to 5.5V

Junction Temperature Range

-40�C to 125�C

Electrical Characteristics

= 5V, C

= 1

�F, T

= 25

�C, for each LDO unless otherwise specified)

Parameter Symbol Test

Conditions Min

Typ

Max Units

OUT1

OUT

= 1mA

3.315 3.35 3.415

OUT2

OUT

= 1mA

2.525 2.55 2.60

RT9185A

1.782 1.8 1.836

Output Voltage Accuracy

OUT3

RT9185B

OUT

= 1mA

1.485 1.5 1.530

LIM1

LOAD

= 1

1.5

1.9

LIM2

LOAD

= 1

0.8

1.3

Current Limiting

LIM3

LOAD

= 1

0.3

0.5

Quiescent Current (triple LDOs)
(Note 5)

OUT

= 0mA

-- 0.4 0.8

DROP1

OUT

= 1.0A

-- 600

1085

Dropout Voltage

DROP2

OUT

= 0.8A

-- 700 --

Line Regulation (triple LDOs)

LINE

OUT

= 1mA, V

= 4V to 6V

-- 2 10

LOAD1

OUT1

, 1mA

< I

OUT

<1.0A

LOAD2

OUT2

, 1mA

< I

OUT

<0.8A --

Load Regulation (Note 4)

LOAD3

OUT3

, 1mA

< I

OUT

< 0.3A

Temperature Coefficient

-- 30 --

PPM

Thermal Shutdown

125 165 --

�C

RT9185

www.richtek.com

DS9185-02 July 2003

Note 1. Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device.

These are stress ratings only, and functional operation of the device at these or any other conditions beyond those
indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.

Note 2. Devices are ESD sensitive. Handling precaution recommended. The human body model is a 100pF capacitor

discharged through a 1.5K

resistor into each pin.

Note 3. The device is not guaranteed to function outside its operating conditions.
Note 4. Regulation is measured at constant junction temperature by using a 20mS current pulse. Devices are tested for load

regulation in the load range from 1mA to 1.5A, 0.8A and 0.3A for each LDO respectively.

Note 5. Quiescent, or ground current, is the difference between input and output currents. It is defined by I

= I

� I

OUT

under no load condition (I

OUT

= 0mA). The total current drawn from the supply is the sum of the load current plus the

ground pin current.

RT9185

DS9185-02 July 2003

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Typical Operating Characteristics

Load1

(A)

Short Thermal Shutdown

2.5

1.5

0.5

Time 25mS/Div

= 5V

= 2.2

�F

= 25�C

= 5V

OUT1

OUT2

OUT3

Current Limit vs. Temperature

0.5

1.5

2.5

-35

-15

105

125

Temperature ( C)

Cur

r
ent

i
t
(

)

-40

(�C)

PSRR

-80

-70

-60

-50

-40

-30

-20

-10

100

1000

10000

100000

10000

Frequency (Hz)

PSRR (

10 100 1K 10K 100K 1M

OUT1

OUT2

OUT3

= 5V

=2.2

�F, C

= 4.7

�F

=4.7

�F, C

= 1

�F

, I

= 10mA

=25�C

= 5V

Dropout Valtage vs. Temperature

0.2

0.4

0.6

0.8

-35

-15

105

125

Temperature ( C)

out

l
t
ag

e (

)

OUT1

= 3.3V

OUT2

= 2.5V

-40

(�C)

OUT1

= 3.3V

OUT2

= 2.5V

OUT3

= 1.8V/1.5V

Temperature Stability

1.4

1.8

2.2

2.6

3.4

3.8

4.2

-35

-15

105

125

Temperature ( C)

t
V

lt
a

)

-40

�

= 5V

OUT1

OUT2

OUT3

(�C)

Quiescent Current

200

300

400

500

600

-35

-15

105

125

Temperature

(
�
A)

-40

RT9185

www.richtek.com

DS9185-02 July 2003

=5V

OUT3

=1.5V

=25�C

=2.2

�

Load Current

(mA)

Output Voltage Deviation (mV)

400

200

100

-50

Time 500

�

S/Div

Load Transient Response

Time 500

�

S/Div

= 5V

OUT1

= 3.3V

= 25�C

= 2.2

�

= 4.7

�

Load Current

(A)

Output Voltage Deviation (mV)

100

-50

= 5V

OUT2

= 2.5V

= 25�C

= 2.2

�

= 4.7

�

Load Current

(A)

Output Voltage Deviation (mV)

100

-50

Time 500

�

S/Div

Load Transient Response

= 4.5V to 5.5V

OUT1

= 3.3V

= 25�C

= 2.2

�

= 4.7

�

OUT1

= 500mA

Input Voltage Deviation (V)

Output Voltage Deviation (mV)

5.5

4.5

-5

Time 100

�

S/Div

Line Transient Response

= 4.5V to 5.5V

OUT2

= 2.5V

= 25�C

= 2.2

�

= 4.7

�

OUT1

= 400mA

Output Voltage Deviation (mV)

5.5

4.5

-10

Time 100

�

S/Div

Line Transient Response

Input Voltage Deviation (V)

= 4.5V to 5.5V

OUT1

= 1.5V

= 25�C

= 2.2

�

= 4.7

�

OUT1

= 150mA

Input Voltage Deviation (V)

Output Voltage Deviation (mV)

5.5

4.5

-10

Time 100

�

S/Div

Line Transient Response

RT9185

www.richtek.com

DS9185-02 July 2003

Applications Information

Like any low-dropout regulator, the RT9185 requires
input and output decoupling capacitors. The device is
specifically designed for portable applications
requiring minimum board space and smallest
components. These capacitors must be correctly
selected for good performance (see Capacitor
Characteristics Section). Please note that linear
regulators with a low dropout voltage have high
internal loop gains which require care in guarding
against oscillation caused by insufficient decoupling
capacitance.

INPUT CAPACITOR
An input capacitance of

2.2�F is required between

the device input pin and ground directly (the amount
of the capacitance may be increased without limit).
The input capacitor MUST be located less than 1 cm
from the device to assure input stability (see PCB
Layout Section). A lower ESR capacitor allows the
use of less capacitance, while higher ESR type (like
aluminum electrolytic) require more capacitance.

Capacitor types (aluminum, ceramic and tantalum)
can be mixed in parallel, but the total equivalent input
capacitance/ESR must be defined as above to stable
operation.

There are no requirements for the ESR on the input
capacitor, but tolerance and temperature coefficient
must be considered when selecting the capacitor to
ensure the capacitance will be

2.2�F over the entire

operating temperature range.

OUTPUT CAPACITOR
The RT9185 is designed specifically to work with
very small ceramic output capacitors. The
recommended minimum capacitance (temperature
characteristics X7R, X5R, Z5U, or Y5V) are 2.2

�F to

4.7

�F range with 10m to 50m range ceramic

capacitors between each LDO output and GND for
transient stability, but it may be increased without
limit. Higher capacitance values help to improve
transient.

The output capacitor's ESR is critical because it
forms a zero to provide phase lead which is required
for loop stability.

NO LOAD STABILITY
The device will remain stable and in regulation with
no external load. This is specially important in CMOS
RAM keep-alive applications.

INPUT-OUTPUT (DROPOUT) VOLTAGE
A regulator's minimum input-to-output voltage
differential (dropout voltage) determines the lowest
usable supply voltage. In battery-powered systems,
this determines the useful end-of-life battery voltage.
Because the device uses a PMOS, its dropout
voltage is a function of drain-to-source on-resistance,
R

DS(ON)

, multiplied by the load current:

DROUPOUT

= V

� V

OUT

= R

DS(ON)

� I

OUT

CURRENT LIMIT
The RT9185 monitors and controls the PMOS' gate
voltage, limiting the output current to 1.9A, 1.3A and
0.5A (typ) respectively. The outputs can be shorted
to ground for an indefinite period of time without
damaging the part.

SHORT-CIRCUIT PROTECTION
The device is short circuit protected and in the event
of a peak over-current condition, the short-circuit
control loop will rapidly drive the output PMOS pass
element off. Once the power pass element shuts
down, the control loop will rapidly cycle the output on
and off until the average power dissipation causes
the thermal shutdown circuit to respond to servo the
on/off cycling to a lower frequency. Please refer to
the section on thermal information for power
dissipation calculations.

CAPACITOR CHARACTERISTICS
It is important to note that capacitance tolerance and
variation with temperature must be taken into
consideration when selecting a capacitor so that the
minimum required amount of capacitance is provided
over the full operating temperature range. In general,

RT9185

DS9185-02 July 2003

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a good tantalum capacitor will show very little
capacitance variation with temperature, but a ceramic
may not be as good (depending on dielectric type).
Aluminum electrolytics also typically have large
temperature variation of capacitance value.

Equally important to consider is a capacitor's ESR
change with temperature: this is not an issue with
ceramics, as their ESR is extremely low. However, it
is very important in tantalum and aluminum
electrolytic capacitors. Both show increasing ESR at
colder temperatures, but the increase in aluminum
electrolytic capacitors is so severe they may not be
feasible for some applications.

Ceramic:
For values of capacitance in the 10

�F to 100�F

range, ceramics are usually larger and more costly
than tantalums but give superior AC performance for
by-passing high frequency noise because of very low
ESR (typically less than 10m

). However, some

dielectric types do not have good capacitance
characteristics as a function of voltage and
temperature.

Z5U and Y5V dielectric ceramics have capacitance
that drops severely with applied voltage. A typical
Z5U or Y5V capacitor can lose 60% of its rated
capacitance with half of the rated voltage applied to it.
The Z5U and Y5V also exhibit a severe temperature
effect, losing more than 50% of nominal capacitance
at high and low limits of the temperature range.

X7R and X5R dielectric ceramic capacitors are
strongly recommended if ceramics are used, as they
typically maintain a capacitance range within �20% of
nominal over full operating ratings of temperature
and voltage. Of course, they are typically larger and
more costly than Z5U/Y5U types for a given voltage
and capacitance.

Tantalum:
Solid tantalum capacitors are recommended for use
on the output because their typical ESR is very close
to the ideal value required for loop compensation.
They also work well as input capacitors if selected to
meet the ESR requirements previously listed.

Tantalums also have good temperature stability: a
good quality tantalum will typically show a
capacitance value that varies less than 10~15%
across the full temperature range of 125�C to

-40�C.

ESR will vary only about 2X going from the high to
low temperature limits.

The increasing ESR at lower temperatures can cause
oscillations when marginal quality capacitors are
used (if the ESR of the capacitor is near the upper
limit of the stability range at room temperature).

Aluminum:
This capacitor type offers the most capacitance for
the money. The disadvantages are that they are
larger in physical size, not widely available in surface
mount, and have poor AC performance (especially at
higher frequencies) due to higher ESR and ESL.

Compared by size, the ESR of an aluminum
electrolytic is higher than either Tantalum or ceramic,
and it also varies greatly with temperature. A typical
aluminum electrolytic can exhibit an ESR increase of
as much as 50X when going from 25�C down to
-40�C.

It should also be noted that many aluminum
electrolytics only specify impedance at a frequency of
120Hz, which indicates they have poor high
frequency performance. Only aluminum electrolytics
that have an impedance specified at a higher
frequency (between 20kHz and 100kHz) should be
used for the device. Derating must be applied to the
manufacturer's ESR specification, since it is typically
only valid at room temperature.

Any applications using aluminum electrolytics should
be thoroughly tested at the lowest ambient operating
temperature where ESR is maximum.

RT9185

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DS9185-02 July 2003

THERMAL CONSIDERATIONS

The RT9185 is a triple channel CMOS regulator
designed to provide two output voltage from one
package. Each output pin the RT9185 can deliver a
current of up to 1.5A, 0.8A and 0.3A respectively
over the full operating junction temperature range.
However, the maximum output current must be
derated at higher ambient temperature to ensure the
junction temperature does not exceed 125

�C. With all

possible conditions, the junction temperature must be
within the range specified under operating conditions.
Each regulator contributes power dissipation to the
overall power dissipation of the package. Power
dissipation can be calculated based on the output
current and the voltage drop across each regulator.

= (V

�V

OUT1

) I

OUT1

+ (V

� V

OUT2

) I

OUT2

� V

OUT3

) I

OUT3

+ V

GND

Although the device is rated for 1.5A, 0.8A and 0.3A
of output current, the application may limit the
amount of output current based on the total power
dissipation and the ambient temperature. The final
operating junction temperature for any set of
conditions can be estimated by the following thermal
equation:

D (MAX)

= ( T

J (MAX)

- T

) /

Where T

J (MAX)

is the maximum junction temperature

of the die (125

�C) and T

is the maximum ambient

temperature.

is the thermal resistance from the

junction to the surrounding environment which is
combined with

. Where

is junction to

case thermal resistance which for fused SOP-8 is
20�C/W, TO-252-5 is 10�C/W and TO-263-5 is
5.5�C/W,

is case to ambient thermal resistance

which depend on PCB board area and air flow.

PCB LAYOUT
The RT9185 is a fixed output voltage regulator which
the voltage are sensed at the output pin. A long PCB
trace to load will cause a voltage drop between load
and RT9185. Be careful with PCB layout which
minimum the output trace length and maximum the
trace width.

The GND pin of the RT9185 performs the dual
function of providing an electrical connection to
ground and channeling heat away. Connect the GND
pin to ground using a large pad or ground plane.

Good board layout practices must be used or
instability can be induced because of ground loops
and voltage drops. The input and output capacitors
MUST be directly connected to the input, output, and
ground pins of the device using traces which have no
other currents flowing through them. The best way to
do this is to layout C

and C

OUT

near the device with

short traces to the V

, V

OUT

, and ground pins.

The regulator ground pin should be connected to the
external circuit ground so that the regulator and its
capacitors have a "single point ground".

It should be noted that stability problems have been
seen in applications where "vias" to an internal
ground plane were used at the ground points of the
device and the input and output capacitors. This was
caused by varying ground potentials at these nodes
resulting from current flowing through the ground
plane. Using a single point ground technique for the
regulator and it's capacitors fixed the problem. Since
high current flows through the traces going into V

and coming from V

OUT

, Kelvin connect the capacitor

leads to these pins so there is no voltage drop in
series with the input and output capacitors.

Optimum performance can only be achieved when
the device is mounted on a PC board according to
the diagram below:

RT9185

VDD VOUT1

VOUT3

VOUT2

GND

GND PLANE

LOAD