MAX15061 [MAXIM]
80V, 300mW Boost Converter and Current Monitor for APD Bias Applications; 80V ， 300mW boost转换器和电流监测器，用于APD偏置
| 型号： | MAX15061 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 80V, 300mW Boost Converter and Current Monitor for APD Bias Applications |
| 文件： | 总16页 (文件大小：405K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-5034; Rev 0; 10/09
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX5061
General Description
Features
o Input Voltage Range
The MAX15061 consists of a constant-frequency pulse-
width modulating (PWM) step-up DC-DC converter with
an internal switch and a high-side current monitor with
high-speed adjustable current limiting. This device can
generate output voltages up to 76V and provides current
monitoring up to 4mA (up to 300mW). The MAX15061
can be used for a wide variety of applications such as
avalanche photodiode biasing, PIN biasing, or varactor
biasing, and LCD displays. The MAX15061 operates
from 2.7V to 11V.
+2.7V to +5.5V (Using Internal Charge Pump) or
+5.5V to +11V
o Wide Output-Voltage Range from (V + 1V) to 76V
IN
o Internal 1Ω (typ) 80V Switch
o 300mW Boost Converter Output Power
o Accurate 10ꢀ (500nA to 1mA) and 3.5ꢀ (1mA
to 4mA) High-Side Current Monitor
o Resistor-Adjustable Ultra-Fast APD Current Limit
The constant-frequency (400kHz), current-mode PWM
architecture provides low-noise output voltage that is
easy to filter. A high-voltage, internal power switch
allows this device to boost output voltages up to 76V.
Internal soft-start circuitry limits the input current when
the boost converter starts. The MAX15061 features a
shutdown mode to save power.
(1µs Response Time)
o Open-Drain Current-Limit Indicator Flag
o 400kHz Fixed Switching Frequency
o Constant PWM Frequency Provides Easy Filtering
in Low-Noise Applications
o Internal Soft-Start
The MAX15061 includes a current monitor with more
than three decades of dynamic range and monitors cur-
rent ranging from 500nA to 2mA with high accuracy.
Resistor-adjustable current limiting protects the APD
from optical power transients. A clamp diode protects
the monitor’s output from overvoltage conditions. Other
protection features include cycle-by-cycle current limit-
ing of the boost converter switch, undervoltage lockout,
and thermal shutdown if the die temperature reaches
+160°C.
o 2µA (max) Shutdown Current
o -40°C to +125°C Temperature Range
o Small Thermally Enhanced, 4mm x 4mm, 16-Pin
TQFN Package
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX15061ATE+
-40°C to +125°C
16 TQFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
The MAX15061 is available in a thermally enhanced
4mm x 4mm, 16-pin TQFN package and operates over
the -40°C to +125°C automotive temperature range.
Pin Configuration
Applications
TOP VIEW
Avalanche Photodiode Biasing and Monitoring
PIN Diode Bias Supplies
Low-Noise Varactor Diode Bias Supplies
FBON Modules
12
11
10
9
ILIM
8
7
6
5
BIAS 13
SHDN 14
GPON Modules
CNTRL
FB
LCD Displays
MAX15061
PGND
LX
15
16
*EP
SGND
+
Typical Operating Circuits appear at end of data sheet.
1
2
3
4
THIN QFN
(4mm × 4mm)
*CONNECT EXPOSED PAD TO SGND.
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
ABSOLUTE MAXIMUM RATINGS
PWR, IN to SGND...................................................-0.3V to +12V
LX to PGND ............................................................-0.3V to +80V
BIAS, APD to SGND ...............................................-0.3V to +80V
Continuous Power Dissipation
16-Pin TQFN (derate 25mW/°C above +70°C)..........2000mW
Thermal Resistance (Note 1)
SHDN to SGND............................................-0.3V to (V + 0.3V)
θ
θ
...............................................................................40°C/W
.................................................................................6°C/W
IN
JA
JC
CLAMP to SGND......................................-0.3V to (V
+ 0.3V)
BIAS
FB, ILIM, RLIM, CP, CN, CNTRL to SGND.............-0.3V to +12V
PGND to SGND .....................................................-0.3V to +0.3V
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
MOUT to SGND....................................-0.3V to (V
+ 0.3V)
CLAMP
Note 1:
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
MAX5061
layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
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
(V = V
= 3.3V. V
= 3.3V. C = C
= 10μF. C = 10nF, V
= V . V
= 0V. V
= V
= 0V. V
SGND
= 40V.
BIAS
PGND
IN
PWR
SHDN
IN
PWR
CP
CNTRL
IN RLIM
APD = unconnected. CLAMP = unconnected. ILIM = unconnected, MOUT = unconnected. T = T = -40°C to +125°C, unless other-
A
J
wise noted. Typical values are at T = +25°C.) (Note 2)
A
PARAMETER
SYMBOL
, V
CONDITIONS
MIN
2.7
TYP
MAX
5.5
11
UNITS
Supply Voltage Range
V
V
IN PWR
CP connected to IN, C = open
5.5
CP
V
V
C
= 1.4V, no switching
1
2
FB
Supply Current
I
mA
SUPPLY
= 11V, V = 1.4V (no switching),
IN
FB
1.2
3
= open, CP = IN
CP
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
Shutdown Current
V
V
rising
IN
2.375
2.5
2.675
V
UVLO
V
100
mV
μA
μA
UVLO_HYS
I
SHDN pulled low
2
IN_SHDN
Bias Current During Shutdown
BOOST CONVERTER
I
V
= 3.3V, V = 0V
SHDN
30
BIAS_SHDN
BIAS
Output-Voltage Adjustment
Range
V
+
1V
IN
76
V
V
= V
= 5V
400
400
90
IN
PWR
Switching Frequency
f
kHz
SW
2.9V ≤ V
2.9V ≤ V
≤ 11V, V = V
IN
PWR
PWR
PWR
PWR
Maximum Duty Cycle
FB Set-Point Voltage
FB Input Bias Current
D
≤ 11V, V = V
%
V
CLK
IN
V
1.2201 1.245 1.2699
100
FB
FB
I
nA
V
V
= V = 2.9V,
IN
= 5.5V
PWR
1
1
2
2
CP
I
I
= 100mA
= 100mA,
LX
V
V
= V = 5.5V,
IN
= 10V
PWR
Internal Switch On-Resistance
R
Ω
ON
CP
V
V
= V = V = 5.5V
1
1
2
2
PWR
PWR
IN
CP
LX
V
= V
IN
CP
= V = V = 11V
IN
CP
Peak Switch Current Limit
LX Leakage Current
I
0.8
1.2
1.6
1
A
LIM_LX
V
= 76V
μA
LX
2.9V ≤ V
≤ 11V, V
= V ,
IN
PWR
PWR
Line Regulation
Load Regulation
0.2
1
%
%
I
= 4.5mA
LOAD
0 ≤ I
≤ 4.5mA
LOAD
2
_______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX5061
ELECTRICAL CHARACTERISTICS (continued)
(V = V
= 3.3V. V
= 3.3V. C = C
= 10μF. C = 10nF, V
= V . V
= 0V. V
= V
= 0V. V
SGND
= 40V.
BIAS
PGND
IN
PWR
SHDN
IN
PWR
CP
CNTRL
IN RLIM
APD = unconnected. CLAMP = unconnected. ILIM = unconnected, MOUT = unconnected. T = T = -40°C to +125°C, unless other-
A
J
wise noted. Typical values are at T = +25°C.) (Note 2)
A
PARAMETER
Soft-Start Duration
SYMBOL
CONDITIONS
MIN
TYP
8
MAX
UNITS
ms
Soft-Start Steps
(0.25 x I
) to I
LIM_LX
32
Steps
LIM_LX
CONTROL INPUT (CNTRL)
Maximum Control Input-Voltage
Range
FB set point is regulated to V
1.25
V
CNTRL
CURRENT MONITOR
Bias Voltage Range
V
10
76
100
3.2
1
V
BIAS
I
I
I
I
I
= 500nA
= 2mA
μA
mA
V
APD
APD
APD
APD
APD
Bias Quiescent Current
I
BIAS
Voltage Drop
V
DROP
R
MOUT
= 2mA, V
= 500nA
= 2.5mA
= V
- V
BIAS APD
DROP
1
890
1
GΩ
MΩ
nA
Dynamic Output Resistance at
MOUT
MOUT Output Leakage
Output Clamp Voltage
APD is unconnected
Forward diode current = 1mA
V = V = 76V
BIAS
V
-
MOUT
0.5
0.73
1
0.95
V
nA
V
V
CLAMP
Output Clamp Leakage Current
Output-Voltage Range
CLAMP
10V ≤ V
is unconnected
≤ 76V, 0 ≤ I
≤ 1mA, clamp
V
-
BIAS
APD
BIAS
1V
V
MOUT
I
I
= 500nA
= 2mA
0.1
0.1
APD
APD
Current Gain
I
/I
MOUT APD
0.0965
-1000
0.1035
+1500
I
I
= 500nA
= 5μA to
+300
APD
(ΔI
V
/I
)/ΔV
,
MOUT MOUT
BIAS
Power-Supply Rejection Ratio
PSRR
= 10V to 76V
ppm/V
BIAS
APD
(Note 3)
= 35V, R = 3.3kΩ
LIM
-250
+24
3.75
+250
1mA
APD Input Current Limit
I
V
3.15
1
4.35
5
mA
mA
LIM_APD
APD
Current-Limit Adjustment Range
12.45kΩ ≥ R
≥ 2.5kΩ
LIM
I
settles to within
MOUT
I
I
= 500nA
= 2.5mA
7.5
90
ms
μs
APD
Power-Up Settling Time
t
0.1%, 10nF connected
from APD to ground
S
APD
LOGIC INPUTS/OUTPUTS
SHDN Input-Voltage Low
SHDN Input-Voltage High
ILIM Output-Voltage Low
ILIM Output Leakage Current
THERMAL PROTECTION
Thermal Shutdown
V
0.8
V
V
IL
V
2.4
IH
V
I
= 2mA
0.3
1
V
OL
OH
LIM
I
V
= 11V
μA
ILIM
Temperature rising
+160
10
°C
°C
Thermal Shutdown Hysteresis
Note 2: All minimum/maximum parameters are tested at T = +125°C. Limits over temperature are guaranteed by design.
A
Note 3: Guaranteed by design and not production tested.
_______________________________________________________________________________________
3
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
Typical Operating Characteristics
(V
= V = 3.3V, V
= 70V, circuit of Figure 3 (Figure 4 for V > 5.5V), unless otherwise noted.)
IN
PWR
IN
OUT
EFFICIENCY vs. LOAD CURRENT
EFFICIENCY vs. LOAD CURRENT
EFFICIENCY vs. LOAD CURRENT
70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
V
= 30V
V
OUT
= 30V
OUT
MAX5061
V
= 8V
IN
V
= 55V
OUT
V
= 55V
OUT
V = 3.3V
IN
V
= 5V
IN
V
= 70V
OUT
V
= 70V
OUT
V
IN
= 3.3V
V
= 5V
V
3
= 70V
OUT
IN
0
1
2
3
4
0
1
2
3
4
0
1
2
4
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MINIMUM STARTUP VOLTAGE
vs. LOAD CURRENT
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
60
50
40
30
20
10
0
2.55
2.54
2.53
2.52
2.51
2.50
2.49
2.48
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
T
A
= -40°C
T
A
= +25°C
T
= +85°C
A
T
A
= +25°C
T
= +85°C
A
T
A
= -40°C
T
A
= +125°C
V
= 1.4V
FB
3
4
5
6
7
8
9
10 11
0
1
2
3
4
0
1
2
3
4
5
6
7
8
9 10 11
SUPPLY VOLTAGE (V)
LOAD CURRENT (mA)
SUPPLY VOLTAGE (V)
EXITING SHUTDOWN
ENTERING SHUTDOWN
MAX15061 toc07
MAX15061 toc08
70V
OUTPUT VOLTAGE
50V/div
V
OUT
50V/div
3V
3V
INDUCTOR CURRENT
500mA/div
I
L
0mA
500mA/div
0mA
SHUTDOWN VOLTAGE
2V/div
V
SHDN
0V
2V/div
I
= 1mA
OUT
I
= 1mA
LOAD
0V
1ms/div
4ms/div
4
_______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX5061
Typical Operating Characteristics (continued)
(V
= V = 3.3V, V
= 70V, circuit of Figure 3 (Figure 4 for V > 5.5V), unless otherwise noted.)
IN
OUT
PWR
IN
LIGHT-LOAD SWITCHING
HEAVY-LOAD SWITCHING
WAVEFORM WITH RC FILTER
WAVEFORM WITH RC FILTER
MAX15061 toc09
MAX15061 toc10
I
= 0.1mA, V
= 70V
I
= 4mA, V
= 70V
OUT
BIAS
OUT
BIAS
V
V
BIAS
BIAS
AC-COUPLED
1mV/div
AC-COUPLED
1mV/div
V
V
LX
LX
50V/div
50V/div
0V
0V
I
I
L
L
500mA/div
0mA
500mA/div
0mA
1μs/div
1μs/div
LX LEAKAGE CURRENT
vs. TEMPERATURE
LOAD-TRANSIENT RESPONSE
LINE-TRANSIENT RESPONSE
MAX15061 toc12
MAX15061 toc11
200
CURRENT INTO
LX PIN
180
160
140
120
100
80
V
IN
2V/div
3.3V
V
OUT
AC-COUPLED
200mV/div
I
LOAD
5mA/div
0mA
V
OUT
AC-COUPLED
100mV/div
60
40
V
I
RISE
= 70V
OUT
OUT
V
V
= 70V
= 3.3V
OUT
IN
= 1mA
20
t
= 50μs
0
-40 -25 -10
5
20 35 50 65 80 95 110 125
100ms/div
100ms/div
TEMPERATURE (°C)
MAXIMUM LOAD CURRENT
vs. INPUT VOLTAGE
BIAS CURRENT
vs. BIAS VOLTAGE
LOAD REGULATION
70.0
110
100
90
80
70
60
50
40
30
20
10
0
10
1
69.8
69.6
69.4
69.2
69.0
68.8
68.6
68.4
68.2
68.0
I
= 2mA
APD
A
B
C
D
I
= 500nA
APD
0.1
0.01
E
F
A: V
OUT
D: V
OUT
= 30V, B: V
= 55V, E: V
= 35V, C: V
= 45V,
= 72V
OUT
OUT
OUT
OUT
= 60V, F: V
0
1
2
3
4
5
3
4
5
6
7
8
9
10 11
0
10 20 30 40 50 60 70 80
BIAS VOLTAGE (V)
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
Typical Operating Characteristics (continued)
(V
= V = 3.3V, V
= 70V, circuit of Figure 3 (Figure 4 for V > 5.5V), unless otherwise noted.)
IN
OUT
PWR
IN
BIAS CURRENT
vs. APD CURRENT
BIAS CURRENT
vs. TEMPERATURE
GAIN ERROR
vs. APD CURRENT
10
1
10
1
5
4
V
= 70V
BIAS
V
= 70V
BIAS
I
= 2mA
APD
3
2
MAX5061
1
0
-1
-2
-3
-4
-5
0.1
0.1
0.01
I
= 500nA
APD
0.01
0.0001 0.001
0.01
0.1
1
10
-40 -25 -10
5
20 35 50 65 80 95 110 125
0.1
1
10
100
(μA)
1000 10,000
APD CURRENT (mA)
TEMPERATURE (°C)
I
APD
GAIN ERROR
GAIN ERROR
vs. BIAS VOLTAGE
vs. TEMPERATURE
0.80
0.60
0.40
0.20
0
1.0
0.5
I
= 2mA
I
= 500μA
APD
APD
I
= 5μA
APD
0
I
= 50μA
APD
I
= 50μA
I
= 5μA
APD
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
APD
I
= 500nA
APD
-0.20
-0.40
-0.60
-0.80
I
= 500nA
APD
I
= 500μA
APD
V
= 70V
BIAS
I
= 2mA
APD
10
20
30
40
50
60
70
80
-40 -25 -10
5
20 35 50 65 80 95 110 125
BIAS VOLTAGE (V)
TEMPERATURE (°C)
APD TRANSIENT RESPONSE
STARTUP DELAY
MAX15061 toc22
MAX15061 toc23
V
APD
AC-COUPLED
70V
2V/div
V
BIAS
20V/div
I
APD
3V
2.5mA/div
0mA
I
MOUT
0.25mA/div
I
MOUT
0mA
20nA/div
I
= 500nA
APD
0nA
20μs/div
200μs/div
6
_______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX5061
Typical Operating Characteristics (continued)
(V
= V = 3.3V, V
= 70V, circuit of Figure 3 (Figure 4 for V > 5.5V), unless otherwise noted.)
IN
OUT
PWR
IN
STARTUP DELAY
STARTUP DELAY
MAX15061 toc24
MAX15061 toc25
V
APD
20V/div
V
APD
2V/div
3V
0V
I
MOUT
50μA/div
I
MOUT
20nA/div
I
= 500nA
APD
I
= 2mA
APD
V
= 5V
BIAS
0nA
0nA
100μs/div
100μs/div
STARTUP DELAY
SHORT-CIRCUIT RESPONSE
MAX15061 toc26
MAX15061 toc27
I
LIM
2V/div
V
BIAS
0V
2V/div
0V
I
BIAS
2mA/div
I
MOUT
V
= 70V
= +85°C
50μA/div
BIAS
I
V
= 2mA
APD
T
A
0mA
= 5V
BIAS
R
= 2kΩ
LIM
0nA
40μs/div
40ms/div
SWITCHING FREQUENCY
vs. TEMPERATURE
VOLTAGE DROP
vs. APD CURRENT
500
480
460
440
420
400
380
360
340
320
300
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0
T
A
= +25°C
T
A
= -40°C
T
A
= +125°C
T
A
= +85°C
-40 -25 -10
5
20 35 50 65 80 95 110 125
0.1
1
10
100
(μA)
1000 10,000
TEMPERATURE (°C)
I
APD
_______________________________________________________________________________________
7
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
Typical Operating Characteristics (continued)
(V
= V = 3.3V, V
= 70V, circuit of Figure 3 (Figure 4 for V > 5.5V), unless otherwise noted.)
IN
OUT
PWR
IN
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
SWITCHING FREQUENCY AND
DUTY CYCLE vs. LOAD CURRENT
MAX15061 toc31
60
50
420
415
410
405
400
395
390
385
380
500
480
460
440
420
400
380
360
340
320
300
DUTY CYCLE
40
30
MAX5061
SWITCHING FREQUENCY
MEASURED AT CN
20
10
0
0
1
2
3
4
2
4
6
8
10
12
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
FB SET-POINT VARIATION
vs. TEMPERATURE
APD OUTPUT RIPPLE VOLTAGE
MAX15061 toc33
1.277
1.267
V
= 2.9V
IN
1.257
1.247
1.237
1.227
1.217
1.207
V
= 5.5V
IN
V
APD
FB RISING
AC-COUPLED, 55V
200μV/div
V
= 2.9V
IN
V
= 5.5V
IN
FB FALLING
-40 -25 -10
5
20 35 50 65 80 95 110 125
TEMPERATURE (°C)
2μs/div
APD OUTPUT RIPPLE VOLTAGE
APD OUTPUT RIPPLE VOLTAGE
MAX15061 toc34
MAX15061 toc35
V
V
APD
APD
AC-COUPLED, 55V
AC-COUPLED, 70V
100μV/div
500μV/div
0.1μF CAPACITOR CONNECTED
0.1μF CAPACITOR CONNECTED
FROM APD TO GND.
FROM APD TO GND.
2μs/div
2μs/div
8
_______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX5061
Pin Description
PIN
NAME
FUNCTION
Boost Converter Input Voltage. PWR powers the switch driver and charge pump. Bypass PWR to PGND with a
ceramic capacitor of 1μF minimum value.
1
PWR
CP
Positive Terminal of the Charge-Pump Flying Capacitor for 2.7V to 5.5V Supply Voltage Operation. Connect
CP to IN when the input voltage is in the 5.5V to 11V range.
2
3
4
5
Negative Terminal of the Charge-Pump Flying Capacitor for 2.7V to 5.5V Supply Voltage Operation. Leave CN
unconnected when the input voltage is in the 5.5V to 11V range.
CN
Input Supply Voltage. IN powers all blocks of the MAX15061 except the switch driver and charge pump.
Bypass IN to PGND with a ceramic capacitor of 1μF minimum value.
IN
Signal Ground. Connect directly to the local ground plane. Connect SGND to PGND at a single point, typically
near the return terminal of the output capacitor.
SGND
Feedback Regulation Input. Connect FB to the center tap of a resistive voltage-divider from the output (V
)
OUT
6
7
FB
to SGND to set the output voltage. The FB voltage regulates to 1.245V (typ) when V
is above 1.5V (typ)
CNTRL
and to V
voltage when V
is below 1.245V (typ).
CNTRL
CNTRL
Control Input for Boost Converter Output-Voltage Programmability. Allows the feedback set-point voltage to be
set externally by CNTRL when CNTRL is less than 1.245V. Pull CNTRL above 1.5V (typ) to use the internal
1.245V (typ) feedback set-point voltage.
CNTRL
8
9
ILIM
RLIM
MOUT
Open-Drain Current-Limit Indicator. ILIM asserts low when the APD current limit has been exceeded.
Current-Limit Resistor Connection. Connect a resistor from RLIM to SGND to program the APD current-limit
threshold.
10
11
12
Current-Monitor Output. MOUT sources a current 1/10 of I
.
APD
CLAMP Clamp Voltage Input. CLAMP is the external potential used for voltage clamping of MOUT.
APD
Reference Current Output. APD provides the source current to the cathode of the photodiode.
Bias Voltage Input. Connect BIAS to the boost converter output (V ) either directly or through a lowpass
OUT
13
14
BIAS
filter for ripple attenuation. BIAS provides the voltage bias for the current monitor and is the current source for
APD.
Active-Low Shutdown Control Input. Apply a logic-low voltage to SHDN to shut down the device and reduce
the supply current to 2μA (max). Connect SHDN to IN for normal operation. Ensure that V
is not greater
SHDN
SHDN
than the input voltage, V
.
IN
Power Ground. Connect the negative terminals of the input and output capacitors to PGND. Connect PGND
externally to SGND at a single point, typically at the return terminal of the output capacitor.
15
16
—
PGND
LX
Drain of Internal 80V n-Channel DMOS. Connect inductor and diode to LX. Minimize the trace area at LX to
reduce switching noise emission.
Exposed Pad. Connect EP to a large contiguous copper plane at SGND potential to improve thermal
dissipation. Do not use as the main SGND connection.
EP
_______________________________________________________________________________________
9
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
Functional Diagram
PWR
OUTPUT ERROR AND CURRENT
COMPARATOR
FB
-A
V
REF
MUX
+A
-C
+C
CNTRL
SGND
LX
SWITCH
CONTROL
LOGIC
80V
DMOS
PEAK CURRENT-LIMIT
COMPARATOR
MAX5061
SOFT-
START
PGND
REFERENCE
COMPARATOR
V
REF
SWITCH
CURRENT
SENSE
CLAMP
CHARGE
PUMP
(DOUBLER)
CN
CP
THERMAL
SHUTDOWN
1x
MOUT
RLIM
V
REF
CURRENT-
LIMIT
ADJUSTMENT
MAX15061
CURRENT
MONITOR
BIAS AND
REFERENCE
10x
CURRENT
LIMIT
CLK
APD
ILIM
IN
UVLO
OSCILLATOR
400kHz
SHDN
BIAS
because there is a conduction path between the out-
put, diode, and switch to ground during the time need-
ed for the diode to turn off and reverse its bias voltage.
To reduce the output noise even further, the LX switch
turns off by taking 10ns typically to transition from ON
to OFF. As a consequence, the positive slew rate of the
LX node is reduced and the current from the inductor
does not “force” the output voltage as hard as would
be the case if the LX switch were to turn off faster.
Detailed Description
The MAX15061 constant-frequency, current-mode, PWM
boost converter is intended for low-voltage systems that
require a locally generated high voltage. This device can
generate a low-noise, high output voltage required for
PIN and varactor diode biasing and LCD displays. The
MAX15061 operates either from +2.7V to +5.5V or from
+5.5V to +11V. For 2.7V to 5.5V operation, an internal
charge pump with an external 10nF ceramic capacitor is
used. For 5.5V to 11V operation, connect CP to IN and
leave CN unconnected.
The constant-frequency (400kHz) PWM architecture
generates an output voltage ripple that is easy to filter.
An 80V vertical DMOS device used as the internal
power switch is ideal for boost converters with output
voltages up to 76V. The MAX15061 can also be used in
other topologies where the PWM switch is grounded,
like SEPIC and flyback converters.
The MAX15061 operates in discontinuous mode in
order to reduce the switching noise caused by reverse-
voltage recovery charge of the rectifier diode. Other
continuous mode boost converters generate large volt-
age spikes at the output when the LX switch turns on
10 ______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX5061
The MAX15061 includes a versatile current monitor
The APD current-monitor range is from 500nA to 4mA,
and the MOUT current-mirror output accuracy is 10%
from 500nA to 1mA of APD current and 3.5% from
1mA to 4mA of APD current.
intended for monitoring the APD, PIN, or varactor diode
DC current in fiber and other applications. The
MAX15061 features more than three decades of
dynamic current ranging from 500nA to 4mA and pro-
vides an output current accurately proportional to the
APD current at MOUT.
Clamping the Monitor
Output Voltage (CLAMP)
CLAMP provides a means for diode clamping the volt-
The MAX15061 also features a shutdown logic input to
disable the device and reduce its standby current to
2μA (max).
age at MOUT; thus, V
is limited to (V
+
CLAMP
MOUT
0.6V). CLAMP can be connected to either an external
supply or BIAS. CLAMP can be left unconnected if volt-
age clamping is not required.
Fixed-Frequency PWM Controller
The heart of the MAX15061 current-mode PWM con-
troller is a BiCMOS multiple-input comparator that
simultaneously processes the output-error signal and
switch current signal. The main PWM comparator uses
direct summing, lacking a traditional error amplifier and
its associated phase shift. The direct summing configu-
ration approaches ideal cycle-by-cycle control over the
output voltage since there is no conventional error
amplifier in the feedback path.
Adjusting the Boost Converter
Output Voltage (FB/CNTRL)
The boost converter output voltage can be set by con-
necting FB to a resistor-divider from V
to ground.
OUT
The set-point feedback reference is the 1.245 (typ)
internal reference voltage when V
> 1.5V and is
< 1.25V.
CNTRL
equal to the CNTRL voltage when V
CNTRL
To change the converter output on the fly, apply a volt-
age lower than 1.25V (typ) to the CNTRL input and
adjust the CNTRL voltage, which is the reference input
The device operates in PWM mode using a fixed-fre-
quency, current-mode operation. The current-mode fre-
quency loop regulates the peak inductor current as a
function of the output error signal.
of the error amplifier when V
< 1.25V (see the
CNTRL
Functional Diagram). This feature can be used to adjust
the APD voltage based on the APD mirror current,
which compensates for the APD avalanche gain varia-
tion with temperature and manufacturing process. As
shown in Figure 4, the voltage signal proportional to the
MOUT current is connected to the analog-to-digital
(ADC) input of the APD module, which then controls the
reference voltage of the boost converter error amplifier
through a digital-to-analog (DAC) block connected to
the CNTRL input. The BIAS voltage and, therefore, the
APD current, are controlled based on the MOUT mirror
current, forming a negative feedback loop.
The current-mode PWM controller is intended for dis-
continuous conduction mode (DCM) operation. No
internal slope compensation is added to the current
signal.
Charge Pump
At low supply voltages (2.7V to 5.5V), internal charge-
pump circuitry and an external 10nF ceramic capacitor
connected between CP and CN double the available inter-
nal supply voltage to drive the internal switch efficiently.
In the 5.5V to 11V supply voltage range, the charge
pump is not required. In this configuration, disable the
charge pump by connecting CP to IN and leaving CN
unconnected.
Shutdown (SHDN)
The MAX15061 features an active-low shutdown input
(SHDN). Pull SHDN low to enter shutdown. During shut-
down, the supply current drops to 2μA (30μA from
BIAS) (max). However, the output remains connected to
the input through the inductor and the output diode,
holding the output voltage to one diode drop below
PWR when the MAX15061 shuts down. Connect SHDN
to IN for always-on operation.
Monitor Current Limit (RLIM)
The current limit of the current monitor is programmable
from 1mA to 5mA. Connect a resistor from RLIM to
ground to program the current-limit threshold up to 5mA.
The current monitor mirrors the current out of APD with
a 1:10 ratio, and the MOUT current can be converted to
a voltage signal by connecting a resistor from MOUT to
SGND.
______________________________________________________________________________________ 11
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
output current in amperes, L is the inductor value in
microhenrys, and η is the efficiency of the boost con-
verter (see the Typical Operating Characteristics).
V
OUT
Determining the Inductor Value
Three key inductor parameters must be specified for
operation with the MAX15061: inductance value (L),
R
R
2
1
inductor saturation current (I
), and DC resistance
SAT
FB
(DCR). In general, the inductor should have a saturation
current rating greater than the maximum switch peak
MAX15061
current-limit value (I
= 1.6A). Choose an inductor
LIM-LX
MAX5061
with a low-DCR resistance for reasonable efficiency.
Use the following formula to calculate the lower bound
of the inductor value at different output voltages and
output currents. This is the minimum inductance value
for discontinuous mode operation for supplying full
300mW of output power.
Figure 1. Adjustable Output Voltage
2 × T ×I
× (V − V
OUT IN_MIN
)
S
OUT
L
[μH] =
MIN
2
η×I
LIM-LX
Design Procedure
where V
, V
(both in volts), and I
(in
OUT
IN_MIN
OUT
Setting the Output Voltage
Set the MAX15061 output voltage by connecting a resis-
tive divider from the output to FB to SGND (Figure 1).
amperes) are typical values (so that efficiency is opti-
mum for typical conditions), T (in microseconds) is the
S
period, η is the efficiency, and I
switch current in amperes (see the Electrical
Characteristics table).
is the peak
LIM_LX
Select R (FB to SGND resistor) between 200kΩ and
1
400kΩ. Calculate R (V
lowing equation:
to FB resistor) using the fol-
2
OUT
Calculate the optimum value of L (L
) to ensure
OPTIMUM
the full output power without reaching the boundary
between continuous conduction mode (CCM) and DCM
using the following formula:
⎡
⎢
⎣
⎤
⎛
⎞
V
OUT
R
= R
− 1
⎥
⎦
2
1
⎜
⎟
V
⎝
⎠
REF
where V
can range from (V + 1V) to 76V and V
IN
REF
CNTRL
> 1.5V, the internal 1.245V (typ) reference
OUT
= 1.245V or V
L
[μH]
2.25
MAX
depending on the V
value.
CNTRL
L
[μH] =
OPTIMUM
For V
CNTRL
voltage is used as the feedback set point (V
=
REF
2
V
(V
− V
)× T × η
1.245V) and for V
< 1.25V, V
= V
.
OUT
IN_MIN S
CNTRL
REF
CNTRL
IN_MIN
where L
[μH] =
MAX
2
× V
2 ×I
Determining Peak Inductor Current
If the boost converter remains in the discontinuous
mode of operation, then the approximate peak inductor
current, I
mula below:
OUT
OUT
For a design in which V = 3.3V, V
= 70V, I
=
=
IN
OUT
S
OUT
MIN
3mA, η = 45%, I
1.3μH and L
MAX
= 1.3A, and T = 2.5μs: L
(in amperes), is represented by the for-
LIM-LX
LPEAK
= 23μH.
For a worse-case scenario in which V = 2.9V, V
=
=
IN
OUT
70V, I
= 4mA, η = 43%, I
= 1.3A, and T
2 × T × (V
− V ) ×I
IN_MIN OUT_MAX
OUT
LIM-LX S
= 15μH.
MAX
S
OUT
I
=
LPEAK
2.5μs: L
= 1.8μH and L
MIN
η× L
The choice of 4.7μH is reasonable given the worst-case
scenario above. In general, the higher the inductance,
the lower the switching noise. Load regulation is also
better with higher inductance.
where T is the switching period in microseconds,
S
V
is the output voltage in volts, V
is the mini-
OUT
IN_MIN
is the maximum
mum input voltage in volts, I
OUT_MAX
12 ______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX5061
For very low output ripple applications, the output of the
boost converter can be followed by an RC filter to further
Diode Selection
The MAX15061’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommend-
ed for most applications because of their fast recovery
time and low forward-voltage drop. Ensure that the
diode’s peak current rating is greater than the peak
inductor current. Also the diode reverse-breakdown
reduce the ripple. Figure 2 shows a 100Ω (R ), 0.1μF
F
(C ) filter used to reduce the switching output ripple to
F
1mV
with a 0.1mA load or 2mV
with a 4mA load.
P-P
P-P
The output-voltage regulation resistor-divider must remain
connected to the diode and output capacitor node.
voltage must be greater than V
of the boost converter.
, the output voltage
OUT
Use X7R ceramic capacitors for more stability over the full
temperature range. Use an X5R capacitor for -40°C to
+85°C applications.
Output Filter Capacitor Selection
For most applications, use a small output capacitor of
0.1μF or greater. To achieve low output ripple, a capaci-
tor with low ESR, low ESL, and high capacitance value
should be selected. If tantalum or electrolytic capacitors
are used to achieve high capacitance values, always
add a smaller ceramic capacitor in parallel to bypass
the high-frequency components of the diode current.
The higher ESR and ESL of electrolytic capacitors
increase the output ripple and peak-to-peak transient
voltage. Assuming the contribution from the ESR and
capacitor discharge equals 50% (proportions may vary),
calculate the output capacitance and ESR required for a
specified ripple using the following equations:
Input Capacitor Selection
Bypass PWR to PGND with a 1μF (min) ceramic capaci-
tor and bypass IN to PGND with a 1μF (min) ceramic
capacitor. Depending on the supply source imped-
ance, higher values may be needed. Make sure that the
input capacitors are close enough to the IC to provide
adequate decoupling at IN and PWR as well. If the lay-
out cannot achieve this, add another 0.1μF ceramic
capacitor between IN and PGND (or PWR and PGND)
in the immediate vicinity of the IC. Bulk aluminum elec-
trolytic capacitors may be needed to avoid chattering
at low input voltage. In case of aluminum electrolytic
capacitors, calculate the capacitor value and ESR of
the input capacitor using the following equations:
⎡
⎢
⎤
⎥
I
I
x L
OUT
LPEAK OPTIMUM
C
[μF] =
T −
S
OUT
⎡
⎢
⎤
⎥
V
x I
OUT
x 0.5 x ΔV
IN
I
LPEAK
T −
S
x L
x V
OUT
OUT
OPTIMUM
(V − V
0.5 x ΔV
(V
− V
)
⎢
⎣
⎥
⎦
OUT
OUT IN_MIN
C
[μF] =
IN
η x V
IN_MIN
V
)
⎢
⎣
⎥
⎦
IN_MIN OUT IN_MIN
0.5x ΔV
OUT
OUT
0.5x ΔV x η x V
IN IN_MIN
ESR mΩ =
[
]
ESR mΩ =
[
]
I
V
x I
OUT OUT
L1
C
IN
R
F
100Ω
D1
IN
V
= 2.7V TO 5.5V
PWR
LX
V
OUT
IN
CNTRL
SHDN
R
R
2
1
C
0.1μF
F
FB
C
OUT1
MAX15061
SGND
CP
C
CP
C
PWR
CN
BIAS
PGND
Figure 2. Typical Operating Circuit with RC Filter
______________________________________________________________________________________ 13
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
protection is less critical when MOUT is connected
Determining Monitor Current Limit
directly to subsequent transimpedance amplifiers (linear
or logarithmic) that have low-impedance, near-ground-
referenced inputs. If a transimpedance amplfier is used
on the low side of the photodiode, its voltage drop must
also be considered. Leakage from the clamping diode
is most often insignificant over nominal operating condi-
tions, but grows with temperature.
Calculate the value of the monitor current-limit resistor,
LIM
R
, for a given APD current limit, I
, using the fol-
LIMIT
lowing equation:
1.245V
R
= 10 ×
LIM
I
(mA)
LIMIT
The R
resistor, R , ranges from 12.45kΩ to 2.5Ω
LIM
for APD currents from 1mA to 5mA.
LIM
To maintain low levels of wideband noise, lowpass filter-
ing the output signal is suggested in applications where
only DC measurements are required. Connect the filter
capacitor at MOUT. Determining the required filtering
components is straightforward, as the MAX15061
exhibits a very high output impedance of 890MΩ.
MAX5061
Applications Information
Using APD or PIN Photodiodes
in Fiber Applications
When using the MAX15061 to monitor APD or PIN pho-
todiode currents in fiber applications, several issues
must be addressed. In applications where the photodi-
ode must be fully depleted, keep track of voltages bud-
geted for each component with respect to the available
supply voltage(s). The current monitors require as
much as 1.1V between BIAS and APD, which must be
considered part of the overall voltage budget.
In some applications where pilot tones are used to identi-
fy specific fiber channels, higher bandwidths are desired
at MOUT to detect these tones. Consider the minimum
and maximum currents to be detected, then consult the
frequency response and noise typical operating curves.
If the minimum current is too small, insufficient bandwidth
could result, while too high a current could result in
excessive noise across the desired bandwidth.
Additional voltage margin can be created if a negative
supply is used in place of a ground connection, as long
as the overall voltage drop experienced by the
MAX15061 is less than or equal to 76V. For this type of
application, the MAX15061 is suggested so the output
can be referenced to “true” ground and not the negative
supply. The MAX15061’s output current can be refer-
enced as desired with either a resistor to ground or a
transimpedance amplifier. Take care to ensure that out-
put voltage excursions do not interfere with the required
margin between BIAS and MOUT. In many fiber applica-
tions, MOUT is connected directly to an ADC that oper-
ates from a supply voltage that is less than the voltage
at BIAS. Connecting the MAX15061’s clamping diode
output, CLAMP, to the ADC power supply helps avoid
damage to the ADC. Without this protection, voltages
can develop at MOUT that might destroy the ADC. This
Layout Considerations
Careful PCB layout is critical to achieve low switching
losses and clean and stable operation. Protect sensitive
analog grounds by using a star ground configuration.
Connect SGND and PGND together close to the device
at the return terminal of the output bypass capacitor.
Do not connect them together anywhere else. Keep all
PCB traces as short as possible to reduce stray capaci-
tance, trace resistance, and radiated noise. Ensure that
the feedback connection to FB is short and direct.
Route high-speed switching nodes away from the sen-
sitive analog areas. Use an internal PCB layer for SGND
as an EMI shield to keep radiated noise away from the
device, feedback dividers, and analog bypass capaci-
tors. Refer to the MAX15061 evaluation kit data sheet
for a layout example.
14 ______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX5061
L1
4.7μH
D1
V
IN
V
(70V MAX)
OUT
R
R
2
F
C
0.1μF
OUT
348kΩ
100Ω
C
PWR
1μF
R
ADJ
C
F
0.1μF
PWR
LX
R
1
CNTRL
IN
PGND
6.34kΩ
C
1μF
IN
BIAS
FB
MAX15061
CP
CN
SHDN
ILIM
GPIO
GPIO
C
10nF
CP
V
DD
μC
CLAMP
V
DD
RLIM SGND APD MOUT
ADC
DAC
APD
R
LIM
2.87kΩ
C
MOUT
R
MOUT
(OPTIONAL)
10kΩ
Figure 3. Typical Operating Circuit for V = 2.7V to 5.5V
IN
______________________________________________________________________________________ 15
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
L1
4.7μH
D1
V
IN
= 5.5V TO 11V
V
(70V MAX)
OUT
R
R
2
F
C
0.1μF
OUT
348kΩ
100Ω
C
PWR
1μF
C
F
0.1μF
PWR
LX
MAX5061
R
1
CNTRL
IN
PGND
634kΩ
C
1μF
IN
BIAS
FB
CP
CN
MAX15061
SHDN
ILIM
GPIO
GPIO
V
DD
μC
CLAMP
V
DD
RLIM SGND APD MOUT
ADC
DAC
APD
R
LIM
2.87kΩ
C
MOUT
R
MOUT
(OPTIONAL)
10kΩ
Figure 4. Typical Operating Circuit for V = 5.5V to 11V
IN
Package Information
Chip Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in
the package code indicates RoHS status only. Package draw-
ings may show a different suffix character, but the drawing per-
tains to the package regardless of RoHS status.
PROCESS: BiCMOS
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
16 TQFN
T1644-4
21-0139
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2009 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
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