MAXIM MAX8862LESE

19-1117; Rev 0; 8/96
Low-Cost, Low-Dropout, Dual Linear Regulator
________________________Applications
Cellular Phones
Cordless Phones
PCS Phones
PCMCIA Cards
Modems
Hand-Held Instruments
Electronic Planners
____________________________Features
♦ Low Cost
♦ Guaranteed 250mA and 100mA Output Currents,
with Current Limiting
♦ Dual Mode Operation:
Fixed or Adjustable Output from +2V to +11V
♦ +2.5V to +11.5V Input Range
♦ 160mV Dropout Voltage at 200mA Output Current
♦ Low Supply Current—Even in Dropout
200µA Operating
<1µA Shutdown
♦ Power-Good Indicator
♦ Reverse-Battery Protection
♦ Thermal Overload Protection
______________Ordering Information
PART*
TEMP. RANGE
PIN-PACKAGE
MAX8862_ESE
-40°C to +85°C
16 Narrow SO
*Insert the desired suffix letter (from the table below) into the
blank to complete the part number.
SUFFIX
FIXED OUTPUT VOLTAGE (V)
L
4.95
T
R
3.175
2.85
__________________Pin Configuration
__________Typical Operating Circuit
TOP VIEW
INPUT 1
2.5V TO 11.5V
SHDN1
1µF
SHDN2
MAX8862
OUTPUT 1
AT 250mA
INPUT 2
2.5V TO 11.5V
IN2
IN1
OUT1
OUT2
3.3µF
1µF
OUTPUT 2
AT 100mA
2.2µF
100k
PWROK1
REF2
GND SET1 SET2 GND
0.1µF
IN1 1
16 N.C.
SHDN1 2
15 SET1
PWROK1 3
14 OUT1
GND 4
MAX8862
13 GND
GND 5
12 GND
OUT2 6
11 REF2
SET2 7
10 SHDN2
N.C. 8
9
IN2
Narrow SO
Dual Mode is a trademark of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX8862
_______________General Description
The MAX8862 low-cost, low-dropout, dual linear voltage
regulator is ideal for battery-powered and portable
applications. The regulators have independent supply
inputs and provide 250mA and 100mA, respectively,
with a full-load dropout voltage of 160mV. Both regulators use P-channel MOSFET pass transistors and maintain low quiescent current independent of load current.
In dropout, the MOSFET does not suffer from excessive
base currents, as do saturated PNP transistors.
The MAX8862 output voltage is preset to 4.95V (L),
3.175V (T), or 2.85V (R). This device employs Dual
Mode™ operation, allowing user-adjustable outputs
from +2V to +11V with external resistors. The input
supply-voltage range is 2.5V to 11.5V. Other features
include independent shutdown, power-good indicator,
short-circuit and reverse-battery protection, and thermal shutdown.
The MAX8862’s regulators are ideal power supplies for
the radio and the microcontroller (µC) used in digital,
cordless, and PCS phones. The main regulator is optimized for superior transient and dynamic response,
while the secondary regulator exhibits low-output, wideband noise.
The MAX8862 comes in a 16-pin SO package with a
lead frame that uses multiple GND pins as a heat sink
for additional thermal dissipation.
MAX8862
Low-Cost, Low-Dropout, Dual Linear Regulator
ABSOLUTE MAXIMUM RATINGS
IN1, IN2 to GND (Note 1).....................................................±12V
SET1, SHDN1, PWROK1 to GND.............. -0.3V to (VIN1 + 0.3V)
SET2, SHDN2, REF2 to GND ....................... -0.3V, (VIN2 + 0.3V)
Output Short-Circuit Duration ............................................Infinite
Continuous Power Dissipation (TA = +70°C)
16-Pin Narrow SO (derate 20mW/°C above +70°C) ............... 1W
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature .....................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10sec) ............................ +300°C
Note 1: Connect SHDN1 to IN1 and SHDN2 to IN2 through 20kΩ resistors to limit current flow in case a battery is reversed.
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.
ELECTRICAL CHARACTERISTICS (Notes 2, 3)
(VIN_ = VOUT_(TYP) + 1V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
Input Voltage Range
Output Voltage
0mA < IOUT1 ≤ 250mA,
0mA < IOUT2 ≤ 100mA
Current Limit
Dropout Voltage (Note 4)
UNITS
11.5
V
4.80
4.95
5.15
MAX8862T
3.050
3.175
3.300
MAX8862R
2.75
2.85
2.95
2
VIN1 = 2.5V min, VOUT1 = 2V
250
VIN2 = 2.5V min, VOUT2 = 2V
100
11
580
IOUT2
250
200
330
µA
VIN1 = VIN2 = 11.5V
0.01
1
µA
IOUT1 = IOUT2 = 1mA
1.5
IOUT1 = 200mA, MAX8862L/T
160
330
IOUT2 = 100mA, MAX8862L/T
160
350
IOUT1 = 200mA, MAX8862R
165
350
IOUT2 = 100mA, MAX8862R
180
400
VIN1 = (VOUT1 (TYP) + 1V)
to 11.5V
0.03
0.1
VIN2 = (VOUT2 (TYP) + 1V)
to 11.5V
0.02
0.08
IOUT1 = IOUT2 = 15mA
OUT2 Voltage Noise
V
mA
mA
Line Regulation
Load Regulation
V
IOUT1
Quiescent Current
Shutdown Supply Current
MAX
MAX8862L
Output Voltage Range
Maximum Output Current
TYP
2.5
mV
%/V
IOUT1 = 0mA to 250mA, COUT1 = 3.3µF
0.015
IOUT2 = 0mA to 100mA, COUT2 = 2.2µF
0.02
COUT2 = 2.2µF
ZOUT2 = 10mA
10Hz < f < 100kHz
277
10Hz < f < 1MHz
875
COUT2 = 100µF
ZOUT2 = 10mA
10Hz < f < 100kHz
211
10Hz < f < 1MHz
667
%/mA
µVRMS
mVRMS
REFERENCE
REF2 Output Voltage
CREF2 = 0.1µF
REF2 Line Regulation
VIN2 = 2.5V to 11.5V
1
mV
REF2 Load Regulation
IREF2 = 0µA to 10µA
6
mV
2
1.230
1.250
_______________________________________________________________________________________
1.270
V
Low-Cost, Low-Dropout, Dual Linear Regulator
(VIN_ = VOUT_(TYP) + 1V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
1.175
1.200
1.225
UNITS
PWROK1 OUTPUT
PWROK1 Trip Voltage
Falling edge at SET1
PWROK1 Hysteresis
Rising edge at SET1
PWROK1 Leakage Current
VPWROK1 = 11.5V
PWROK1 Low Voltage
ISINK = 0.5mA
SHDN_ Logic Low
Shutdown mode, VIN_ = VOUT_(TYP) + 1V to 11.5V
SHDN_ Logic High
Active mode, VIN_ = 11.5V
SHDN_ Leakage Current
V SHDN_ = 11.5V
SHDN
15
V
mV
0.01
1
µA
25
200
mV
0.45
V
0.01
1
µA
1.25
1.28
V
0.01
0.1
µA
1.8
V
SET_ INPUT
SET_ Reference Voltage
SET_ = OUT_, IOUT1 = IOUT2 = 15mA
SET_ Input Bias Current
VSET_ = 1.30V
1.23
Internal feedback
SET_ Threshold
40
External feedback
250
mV
THERMAL PROTECTION
Thermal Shutdown Temperature
160
Thermal Shutdown Hysteresis
20
°C
ELECTRICAL CHARACTERISTICS (Notes 2, 3)
(VIN_ = VOUT_(TYP) + 1V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
Input Voltage Range
0mA < IOUT1 ≤ 250mA,
0mA < IOUT2 ≤ 100mA
Output Voltage
Output Voltage Range
Maximum Output Current
Current Limit
Dropout Voltage (Note 4)
MAX
UNITS
11.5
V
MAX8862L
4.80
4.95
MAX8862T
3.050
3.175
3.300
MAX8862R
2.740
2.85
2.960
2
VIN1 = 2.5V min, VOUT1 = 2V
250
VIN2 = 2.5V min, VOUT2 = 2V
100
5.15
11
V
V
mA
IOUT1
580
IOUT2
250
200
330
µA
VIN1 = VIN2 = 11.5V
0.01
1
µA
IOUT1 = IOUT2 = 1mA
1.5
IOUT1 = 200mA, MAX8862L/T
160
330
IOUT2 = 100mA, MAX8862L/T
160
350
IOUT1 = 200mA, MAX8862R
165
350
IOUT2 = 100mA, MAX8862R
180
400
Quiescent Current
Shutdown Supply Current
TYP
2.5
mA
mV
_______________________________________________________________________________________
3
MAX8862
ELECTRICAL CHARACTERISTICS (Notes 2, 3)
MAX8862
Low-Cost, Low-Dropout, Dual Linear Regulator
ELECTRICAL CHARACTERISTICS (Notes 2, 3) (continued)
(VIN_ = VOUT_(TYP) + 1V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
IOUT1 = IOUT2 = 15mA
MIN
TYP
MAX
VIN1 = (VOUT1 (TYP) + 1V)
to 11.5V
0.03
0.12
VIN2 = (VOUT2 (TYP) + 1V)
to 11.5V
0.02
0.10
Line Regulation
Load Regulation
UNITS
%/V
IOUT1 = 0 to 250mA, COUT1 = 3.3µF
0.015
COUT2 = 2.2µF, 10Hz < f < 1MHz, IOUT2 = 10mA
0.02
C = 2.2µF, ZOUT2 = 10mA
OUT2 Voltage Noise
C = 100µF, ZOUT2 = 10mA
%/mA
10Hz < f < 100kHz
-
277
-
10Hz < f < 1MHz
-
875
-
10Hz < f < 100kHz
-
211
-
10Hz < f < 1MHz
-
667
-
1.217
1.250
1.277
µVRMS
REFERENCE
REF2 Output Voltage
CREF2 = 0.1µF
REF2 Line Regulation
VIN2 = 2.5V to 11.5V
1
mV
V
REF2 Load Regulation
IREF2 = 0µA to 10µA
6
mV
PWROK1 OUTPUT
PWROK1 Trip Voltage
Falling edge at SET1
PWROK1 Hysteresis
Rising edge at SET1
PWROK1 Leakage Current
VPWROK1 = 11.5V
PWROK1 Low Voltage
ISINK = 0.5mA
SHDN_ Logic Low
Shutdown mode, VIN_ = VOUT_(TYP) + 1V to 11.5V
SHDN_ Logic High
Active mode, VIN_ = 11.5V
SHDN_ Leakage Current
V SHDN_ = 11.5V
SHDN
1.165
1.200
1.235
15
V
mV
0.01
1
µA
25
200
mV
0.45
V
0.02
1
µA
1.250
1.290
V
0.01
0.1
µA
2.0
V
SET_ INPUT
SET_ Reference Voltage
SET_ = OUT_, IOUT1 = IOUT2 = 15mA
SET_ Input Bias Current
VSET_ = 1.30V
SET_ Threshold
1.220
Internal feedback
External feedback
30
250
mV
THERMAL PROTECTION
Thermal Shutdown Temperature
160
Thermal Shutdown Hysteresis
10
°C
Note 2: Guaranteed by design for TA = -40°C.
Note 3: Guaranteed for a junction temperature (TJ) equal to the operating temperature range. E-grade parts are guaranteed by
design to operate up to TJ = +125°C. For TJ above +125°C, specifications exceed the operating limits.
Note 4: Dropout voltage is (VIN_ - VOUT_) when VOUT_ falls to 100mV below its nominal value at VIN_ = (VOUT_ + 1V). For example,
the MAX8862 is tested by measuring the VOUT_ at (VIN_ = 5.95V for the MAX8862L, VIN_ = 4.175V for the MAX8862T, and
VIN_ = 3.85V for the MAX8862R) then VIN_ is lowered until VOUT_ falls 100mV below the measured value.
4
_______________________________________________________________________________________
Low-Cost, Low-Dropout, Dual Linear Regulator
200
VIN1 = VIN2 = 7V
180
160
140
IQ2
100
IQ1
90
120
100
80
VIN1 = VIN2 = 12V
60
40
20
VIN1 = VIN2 = 7V
0
40
60
20
TEMPERATURE (°C)
100
80
OUT1
3.24
OUT2
3.23
3.22
3.21
100
20
80
40
60
TEMPERATURE (°C)
100
VOUT2
98
97
20
40
60
80
100
4
260
VOUT1/VOUT2
240
3
220
200
(IQ1 + IQ2)
2
180
160
1
140
120
10
1
0.1
LOAD CURRENT (mA)
100
1000
2
3
4
525
5
6 7 8 9 10 11
SUPPLY VOLTAGE (V)
12
OVERSHOOT AND TIME
EXITING SHUTDOWN MODE
MAX8862TOC14
MAX8862TOC07
600
100
0
0.01
DROPOUT VOLTAGE
vs. LOAD CURRENT
DROPOUT VOLTAGE (mV)
0
96
95
0.001
3.20
0
VOUT1
99
-20
MAX8862T
OUTPUT VOLTAGE & QUIESCENT CURRENT
vs. SUPPLY VOLTAGE
MAX8862TOC04
3.26
-20
1000
TEMPERATURE (°C)
101
NORMALIZED OUTPUT VOLTAGE (%)
MAX8862TOC06
3.27
-40
100
OUTPUT VOLTAGE
vs. LOAD CURRENT
OUTPUT VOLTAGE
vs. TEMPERATURE
3.25
10
1
0.1
LOAD CURRENT (mA)
QUIESCENT CURRENT (µA)
-20
0
-40
OUTPUT VOLTAGE (V)
-40
80
0.001 0.01
MAX8862TOC05
100
OUTPUT VOLTAGE (V)
MAX8862 TOC01
MAX8862 TOC03
110
120
SHUTDOWN CURRENT (nA)
220
120
QUIESCENT CURRENT (µA)
QUIESCENT CURRENT (µA)
VIN1 = VIN2 = 12V
MAX8862 TOC02
260
240
SHUTDOWN CURRENT
vs. TEMPERATURE
QUIESCENT CURRENT
vs. LOAD CURRENT
QUIESCENT CURRENT
vs. TEMPERATURE
450
OUT2
1V/div
A
375
0V
300
1V/div
225
OUT1
150
B
75
0V
0
0
40
80
120 160 200 240 280 320
LOAD CURRENT (mA)
20µs/div
VIN1 = 5.3V, IOUT1 = 5mA
A = SHDN1, 0.8V TO 2.4V, 1V/div
B = OUT1, 1V/div
_______________________________________________________________________________________
5
MAX8862
__________________________________________Typical Operating Characteristics
(VIN1 = VIN2 = 5.3V, CIN1 = CIN2 = 1µF, COUT1 = 3.3µF, COUT2 = 2.2µF, SHDN1 = IN1, SHDN2 = IN2. TA = +25°C, unless
otherwise noted.)
MAX8862
Low-Cost, Low-Dropout, Dual Linear Regulator
____________________________Typical Operating Characteristics (continued)
(VIN1 = VIN2 = 5.3V, CIN1 = CIN2 = 1µF, COUT1 = 3.3µF, COUT2 = 2.2µF, SHDN1 = IN1, SHDN2 = IN2. TA = +25°C, unless
otherwise noted.)
OUT2 NOISE AND RIPPLE
OUT1 NOISE AND RIPPLE
MAX8862TOC08
MAX8862TOC09
VOUT
500µV/div
VOUT
1mV/div
5µs/div
5µs/div
IOUT2 = 100mA, AC COUPLED
IOUT1 = 250mA, AC COUPLED
OUT2 LOAD-TRANSIENT RESPONSE
OUT1 LOAD-TRANSIENT RESPONSE
MAX8862TOC11
MAX8862TOC10
300mA
200mA
A
0mA
0mA
A
B
50mV/div
50mV/div
B
2ms/div
2ms/div
VIN2 = 7V, VOUT2 = 3.2V
A = LOAD CURRENT, 0mA TO 200mA, 0.2A/div
B = VOUT2 RIPPLE, 50mV/div, AC COUPLED
VIN1 = 7V, VOUT1 = 3.2V
A = LOAD CURRENT, 0mA TO 300mA, 0.2A/div
B = VOUT1 RIPPLE, 50mV/div, AC COUPLED
OUT1 LINE-TRANSIENT RESPONSE
OUT2 LINE-TRANSIENT RESPONSE
MAX8862TOC13
MAX8862TOC12
6.5V
6.5V
A
A
5.5V
B
50mV/div
1ms/div
IOUT2 = 200mA, VOUT2 = 3.2V
A = VIN2, 5.5V TO 6.5V, 1V/div
B = VOUT2 RIPPLE, 50mV/div, AC COUPLED
6
5.5V
50mV/div
B
1ms/div
IOUT1 = 300mA, VOUT1 = 3.2V
A = VIN1 = 5.5V TO 6.5V, 1V/div
B = VOUT1 RIPPLE, 50mV/div, AC COUPLED
_______________________________________________________________________________________
Low-Cost, Low-Dropout, Dual Linear Regulator
PIN
NAME
1
IN1
FUNCTION
2
SHDN1
3
PWROK1
4, 5, 12, 13
GND
Ground. Connect to a ground plane to maximize thermal dissipation.
6
OUT2
Secondary Regulator Output. Bypass with a 2.2µF low-ESR (< 0.5Ω) capacitor to GND. To improve
load-transient response and noise performance, use a higher-value, lower-ESR capacitor.
7
SET2
OUT2 Voltage-Set Input. Connect to GND for the factory-preset output voltage. Connect to a resistive
divider from OUT2 to GND for adjustable output voltage.
8, 16
N.C.
No connect. There is no internal connection to this pin.
9
IN2
Secondary Regulator Supply Input (2.5V to 11.5V). Bypass with a 1µF, low-ESR capacitor to GND.
10
SHDN2
Secondary Regulator Shutdown Input. A logic-low input turns off the secondary regulator and the
reference.
11
REF2
Secondary Reference Output. Bypass with a 0.1µF capacitor to GND.
14
OUT1
Main Regulator Output. Bypass with a 3.3µF, low-ESR (< 0.5Ω) capacitor to GND. To improve loadtransient response and noise performance, use a higher-value, lower-ESR capacitor.
15
SET1
OUT1 Voltage Set Input. Connect to GND for the factory-preset output voltage. Connect to a
resistive divider from OUT1 to GND for adjustable output voltage.
Main Regulator Supply Input (2.5V to 11.5V). Bypass with a 1µF, low-ESR capacitor to GND.
Main Regulator Shutdown Input. A logic low turns off the main regulator and power-good comparator.
Power-Good Output. This open-drain output is low when VOUT1 is out of regulation (VOUT1 is 4%
lower than its nominal value).
_______________Detailed Description
The MAX8862 features Dual Mode™ operation, allowing a fixed output of 4.95V (L), 3.175V (T), or 2.85V (R),
or an adjustable output from 2V to 11V. The regulator’s
outputs, OUT1 and OUT2, supply 250mA and 100mA,
respectively.
The block diagram (Figure 1) shows the contents of
each regulator. Note that the main regulator provides a
power-good indicator, and the secondary regulator’s
reference output voltage is available at REF2.
The 1.25V bandgap reference is connected to the error
amplifier’s inverting input. The error amplifier compares
this reference with the selected feedback voltage and
amplifies the difference. The MOSFET driver reads the
error signal and applies the appropriate drive to the
P-channel transistor. If the feedback voltage is lower
than the reference, the pass transistor’s gate is pulled
lower, allowing more current to pass and increase the
output voltage. If the feedback voltage is too high, the
pass transistor’s gate is pulled up, allowing less current
to pass to the output.
The output voltage is fed back through either an
internal resistor voltage divider connected to OUT1/
OUT2, or an external resistor network connected to
SET1/SET2. The Dual Mode comparator examines
VSET1/VSET2 and selects the feedback path. If this voltage is below 40mV, internal feedback is used and the
output voltage is regulated to the factory-preset voltage.
Internal P-Channel Pass Transistor
The MAX8862’s P-channel pass transistor provides
several advantages over similar designs using PNP
pass transistors, including longer battery life.
The P-channel MOSFET requires no continuous base
current, thereby reducing quiescent current considerably. PNP regulators normally waste a considerable
amount of current in dropout when the pass transistor
saturates; they also use high base-drive currents under
large loads. The MAX8862 does not suffer from these
problems: it consumes only 200µA of quiescent current
for both regulators under light and heavy loads, as well
as in dropout.
_______________________________________________________________________________________
7
MAX8862
______________________________________________________________Pin Description
MAX8862
Low-Cost, Low-Dropout, Dual Linear Regulator
OUT1
1N1
R1
PWROK1
50mV
BIAS
SHDN1
G1
SET1
1.25V
GND
R2
80mV
GND
IN2
OUT
R3
MAX8862
BIAS
SHDN2
G1
REF2
SET2
1.25V
R4
GND
80mV
GND
Figure 1. Functional Diagram
Output Voltage Selection
Power-Good Comparator
The MAX8862’s Dual Mode operation allows a fixed or
adjustable output voltage. In preset/internal-feedback
mode (SET1/SET2 = GND), output voltages are factory
preset to 4.95V (L), 3.175V (T), or 2.85V (R).
In adjustable/external feedback mode, output voltage is
adjusted between 2V and 11V with two external resistors connected as a voltage divider to SET1/SET2
(Figure 2). Since the input bias current at SET1/SET2 is
<0.1µA, large resistance values can be used for R1
and R2 to minimize power consumption without losing
accuracy. Select R2 in the 10kΩ to 400kΩ range. R1 is
given by:
R1 = R2 (VOUT / VSET - 1)
where VSET = 1.25V.
The MAX8862’s main regulator features a power-good
indicator that asserts when the output voltage falls out
of regulation. In internal-feedback mode, the opendrain PWROK1 output goes low when OUT1 falls 4%
below its nominal value. When used in external feedback mode, PWROK1 goes low when VSET1 falls below
1.2V. A 100kΩ pull-up resistor from PWROK1 to VIN1
provides a logic-control signal. This resistor also minimizes current flow to the input in case the battery is
reversed. PWROK1 can be used to reset a microcontroller or to drive an external LED for indicating a power
failure.
8
_______________________________________________________________________________________
Low-Cost, Low-Dropout, Dual Linear Regulator
MAX8862
OUT_
OUTPUT
R1
SET_
R2
GND
Reverse-Battery Protection
Figure 2. Adjustable Output Voltage
Reference
The MAX8862 provides a precision 1.25V reference at
REF2. Bypass REF2 with a 0.1µF capacitor to ground.
Larger bypassing capacitors will further reduce the
secondary regulator’s wideband noise.
Shutdown
The MAX8862’s regulators have individual shutdown
controls. A logic low on either SHDN1 or SHDN2 turns
off the corresponding internal reference, error comparator, and pass transistors’ control logic, reducing
quiescent current to less than 1µA.
This feature protects the MAX8862 against polarity
reversal at the supply inputs. The inputs can handle
negative voltages up to -12V without suffering any ill
effects. When the input polarity is reversed, the output
will be at the same potential as ground, and no current
will flow from the output back to the input. This feature
protects both the device and the supply-voltage
source. The reverse currents that flow back to the input
are due to RPWROK1 , RSHDN1, and RSHDN2. These
currents are approximately: IREV1 = |VIN1| / (RSHDN1 +
RPWROK1) and IREV2 = |VIN2| / RSHDN2. When operating the MAX8862 in continuous mode (VSHDN1 = VIN1
and VSHDN2 = VIN2) place a resistor (>20kΩ) between
shutdown and supply inputs to limit the current flow in
case the battery is reversed.
Current Limiting
The MAX8862 features a current limit for each regulator. It monitors and controls the pass transistor’s gate
voltage, limiting the output current to 580mA for the
main regulator and 250mA for the secondary regulator.
The current limits apply to all input and output voltage
conditions. The outputs can be shorted to ground for
an indefinite period of time if the package can dissipate
(VIN1 x ILIM1 + VIN2 x ILIM2) without exceeding TJ =
+150°C (see the Power Dissipation and Operating
Region section).
_______________________________________________________________________________________
9
MAX8862
Thermal Overload Protection
Thermal overload protection limits the MAX8862’s total
power dissipation. When the junction temperature
exceeds TJ = +160°C, the thermal sensor sends a signal to the shutdown logic, turning off the pass transistors and allowing the device to cool down. The thermal
sensor turns the pass transistors on again after the IC’s
junction temperature decreases by 20°C. If the thermal
overload condition persists, OUT1 and OUT2 pulse on
and off.
Thermal overload protection is designed to protect the
MAX8862 during fault conditions. For continuous operation, the absolute maximum junction temperature rating of TJ = +150°C should not be exceeded.
MAX8862
Low-Cost, Low-Dropout, Dual Linear Regulator
MAX8862 FIG03
100
R0BA(°C/W)
80
60
40
20
0
0
5
10
15
20
25
35
30
PC-BOARD COPPER FOIL AREA (Cm2)
400
MAXIMUM OUTPUT CURRENT (mA)
(IOUT1 + IOUT2)
MAXIMUM CURRENT
350
(L)
MAX8862FGIG04
Figure 3. Typical Copper Thermal Resistance vs. Copper
Ground Pad Area
pins to ground using a large pad or ground plane.
Where this is impossible, place a copper plane on an
adjacent layer. For a given power dissipation, the pad
should exceed the associated dimensions in Figure 3.
This figure shows a typical thermal resistance for a
35µm-thick copper foil as a function of its area1.
The power dissipation across the device is given by:
P = IOUT1 (VIN1 - VOUT1) + IOUT2 (VIN2 - VOUT2).
The resulting power dissipation is as follows:
P = (TJ - TA) / (θJB + θBA)
where (TJ - TA) is the temperature difference between
the MAX8862 die junction and the surrounding air, θJB
(or θJC) is the thermal resistance of the package, and
θBA is the thermal resistance through the printed circuit
board, copper traces, and other materials to the surrounding air. The MAX8862’s narrow SO package has a
thermal resistance of θJB = +50°C/W.
The MAX8862 regulators deliver the rated output currents and operate with input voltages up to 11.5V, but
not simultaneously. High output currents can only be
sustained when input-output differential voltages are
small, as shown in Figure 4.
(T)
300
(R)
250
(R)
(T)
200
150
(L)
MAXIMUM
SUPPLY
VOLTAGE
100
OPERATING REGION AT
TA = +25°C, TJ = +125°C
50
0
2
3
4
5 6 7 8 9 10 11 12
SUPPLY VOLTAGE (V)
Figure 4. Safe Operating Regions: Main and Secondary
Regulators Maximum Output Current vs. Supply Voltage
__________Applications Information
Power Dissipation and Operating Region
The MAX8862’s maximum power dissipation depends
on the thermal resistance of the case and circuit board,
the temperature difference between the die junction
and ambient air, and the rate of air flow.
The GND pins of the MAX8862 SO package perform
the dual function of providing an electrical connection
to ground and channeling heat away. Connect all GND
Capacitor Selection and
Regulator Stability
Filter capacitors are required at the MAX8862’s inputs
and outputs. 1µF ceramic capacitors are required at
the inputs. The minimum output capacitance required
for stability is 3.3µF for OUT1 and 2.2µF for OUT2. The
capacitor values depend primarily on the desired
power-up time and load-transient response. Loadtransient response is improved by using larger capacitor values. Input and output filter capacitors should be
soldered directly to pins to minimize lead inductance of
PC board traces.
The output capacitor’s equivalent series resistance
(ESR) affects stability and output noise. Surface-mount
ceramic capacitors have a very low ESR and are available up to 10µF. Otherwise, other low-ESR (<0.5Ω)
capacitors should be used. If the selected capacitor’s
ESR is higher than the recommended value, the capacitor value should be increased proportionally to maintain minimum output noise under all input voltage and
output load conditions. Paralleling two or more capacitors also results in lower ESR.
1This
graph was generated by Mr. Kieran O’Malley of Cherry Semiconductor Corp. and was published in the October 26, 1995, issue
of EDN magazine.
10
______________________________________________________________________________________
Low-Cost, Low-Dropout, Dual Linear Regulator
50
OUT1
∆VIN1 = 1Vp-p
CIN1 = 1µF
IOUT1 = 100mA
60
55
40
MAX8862FIG05B
MAX8862FIG05A
A
B
C
70
65
PSRR (dB)
PSRR (dB)
60
OUT1
∆VIN1 = 1Vp-p
CIN1 = 1µF
COUT1 = 3.3µF
MAX8862
70
A
50
B
45
40
35
30
A: IOUT1 = 1mA
B: IOUT1 = 10mA
C: IOUT1 = 100mA
30
25
20
20
0.01
0.1
1
10
A: COUT1 = 100µF
B: COUT1 = 10µF
0.1
100
1
10
100
1000
FREQUENCY (kHz)
FREQUENCY (kHz)
Figure 5a. Power-Supply Rejection Ratio vs. Ripple Frequency
for Light and Heavy Loads
Figure 5b. Power-Supply Rejection Ratio vs. Ripple Frequency
for Various Output Capacitors
Noise
Overshoot and Transient Considerations
The MAX8862’s OUT1 exhibits about 2.5mVp-p, and
OUT2 exhibits 1mVp-p of noise under full-load conditions. When using the MAX8862 for applications that
include analog-to-digital converters (ADCs) with resolutions greater than 12 bits, consider the ADC’s powersupply-rejection specifications.
The Typical Operating Characteristics section shows
power-up, line, and load-transient response graphs.
Typical transients for step changes in the load current
from 0mA to 300mA are 100mVp-p. During recovery
from shutdown, overshoot is minimized by the 1µF
input, and output capacitors (3.3µF for OUT1, and
2.2µF for OUT2).
PSRR and Operation
from Sources Other than Batteries
The MAX8862 is designed to achieve low dropout voltages and low quiescent currents in battery-powered
systems. However, to gain these benefits; the device
must trade away power-supply noise rejection, as well
as swift response to supply variations and load transients. For a 1mA load current, power-supply rejection
typically changes from 58dB to 43dB when the input
frequency is changed from 1Hz to 10kHz. At higher frequencies, the circuit depends primarily on the output
capacitor’s characteristics, and the PSRR increases
(Figure 5).
When operating from sources other than batteries, supply-noise rejection and transient response can be
improved by increasing the value of the input and output capacitors and employing passive filtering techniques. Do not use power supplies with ripple voltages
exceeding 200mV at 100kHz.
Input-Output (Dropout) Voltage
A regulator’s minimum input-to-output voltage differential (or dropout voltage) determines the lowest usable
supply voltage. In battery-powered systems, this determines the useful end-of-life battery voltage. Since
P-channel MOSFETs are used as pass transistors, the
dropout voltage is the product of the RDS(ON) and the
load current (see the Electrical Characteristics).
___________________Chip Information
TRANSISTOR COUNT: 457
______________________________________________________________________________________
11
MAX8862
Low-Cost, Low-Dropout, Dual Linear Regulator
________________________________________________________Package Information
DIM
D
0°-8°
A
0.101mm
0.004in.
e
B
A1
E
C
L
Narrow SO
SMALL-OUTLINE
PACKAGE
(0.150 in.)
H
A
A1
B
C
E
e
H
L
INCHES
MAX
MIN
0.069
0.053
0.010
0.004
0.019
0.014
0.010
0.007
0.157
0.150
0.050
0.244
0.228
0.050
0.016
DIM PINS
D
D
D
8
14
16
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
3.80
4.00
1.27
5.80
6.20
0.40
1.27
INCHES
MILLIMETERS
MIN MAX
MIN
MAX
0.189 0.197 4.80
5.00
0.337 0.344 8.55
8.75
0.386 0.394 9.80 10.00
21-0041A
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1996 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.