19-5034; Rev 0; 10/09
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
Features
The MAX15061 consists of a constant-frequency pulsewidth 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.
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.
The MAX15061 includes a current monitor with more
than three decades of dynamic range and monitors current 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 limiting of the boost converter switch, undervoltage lockout,
and thermal shutdown if the die temperature reaches
+160°C.
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.
o Input Voltage Range
+2.7V to +5.5V (Using Internal Charge Pump) or
+5.5V to +11V
o Wide Output-Voltage Range from (VIN + 1V) to 76V
o Internal 1Ω (typ) 80V Switch
o 300mW Boost Converter Output Power
o Accurate ±10% (500nA to 1mA) and ±3.5% (1mA
to 4mA) High-Side Current Monitor
o Resistor-Adjustable Ultra-Fast APD Current Limit
(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
o 2µA (max) Shutdown Current
o -40°C to +125°C Temperature Range
o Small Thermally Enhanced, 4mm x 4mm, 16-Pin
TQFN Package
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.
RLIM
PIN Diode Bias Supplies
MOUT
TOP VIEW
Avalanche Photodiode Biasing and Monitoring
CLAMP
Pin Configuration
APD
Applications
Ordering Information
12
11
10
9
Low-Noise Varactor Diode Bias Supplies
FBON Modules
GPON Modules
LCD Displays
BIAS 13
8
ILIM
SHDN 14
7
CNTRL
6
FB
5
SGND
MAX15061
PGND 15
LX 16
*EP
+
2
3
4
CN
IN
PWR
1
CP
Typical Operating Circuits appear at end of data sheet.
THIN QFN
(4mm × 4mm)
*CONNECT EXPOSED PAD TO SGND.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX15061
General Description
MAX15061
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
ABSOLUTE MAXIMUM RATINGS
Continuous Power Dissipation
16-Pin TQFN (derate 25mW/°C above +70°C)..........2000mW
Thermal Resistance (Note 1)
θJA ...............................................................................40°C/W
θJC .................................................................................6°C/W
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
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
PWR, IN to SGND ...................................................-0.3V to +12V
LX to PGND ............................................................-0.3V to +80V
BIAS, APD to SGND ...............................................-0.3V to +80V
SHDN to SGND............................................-0.3V to (VIN + 0.3V)
CLAMP to SGND ......................................-0.3V to (VBIAS + 0.3V)
FB, ILIM, RLIM, CP, CN, CNTRL to SGND .............-0.3V to +12V
PGND to SGND .....................................................-0.3V to +0.3V
MOUT to SGND ....................................-0.3V to (VCLAMP + 0.3V)
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.
ELECTRICAL CHARACTERISTICS
(VIN = VPWR = 3.3V. VSHDN = 3.3V. CIN = CPWR = 10μF. CCP = 10nF, VCNTRL = VIN. VRLIM = 0V. VPGND = VSGND = 0V. VBIAS = 40V.
APD = unconnected. CLAMP = unconnected. ILIM = unconnected, MOUT = unconnected. TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETER
Supply Voltage Range
SYMBOL
VIN, VPWR
CONDITIONS
CP connected to IN, CCP = open
MIN
ISUPPLY
VIN = 11V, VFB = 1.4V (no switching),
CCP = open, CP = IN
Undervoltage Lockout Threshold
VUVLO
VIN rising
Undervoltage Lockout Hysteresis
VUVLO_HYS
Shutdown Current
Bias Current During Shutdown
IIN_SHDN
MAX
5.5
5.5
11
VFB = 1.4V, no switching
Supply Current
TYP
2.7
2.375
1
2
1.2
3
2.5
2.675
100
SHDN pulled low
IBIAS_SHDN VBIAS = 3.3V, V SHDN = 0V
UNITS
V
mA
V
mV
2
μA
30
μA
76
V
BOOST CONVERTER
Output-Voltage Adjustment
Range
VIN +
1V
Switching Frequency
fSW
Maximum Duty Cycle
DCLK
FB Set-Point Voltage
VFB
FB Input Bias Current
IFB
VIN = VPWR = 5V
400
2.9V ≤ VPWR ≤ 11V, VIN = VPWR
400
2.9V ≤ VPWR ≤ 11V, VIN = VPWR
Internal Switch On-Resistance
RON
ILX = 100mA,
VCP = VIN
Peak Switch Current Limit
1.245
%
1.2699
V
100
nA
VPWR = VIN = 2.9V,
VCP = 5.5V
1
2
VPWR = VIN = 5.5V,
VCP = 10V
1
2
Ω
VPWR = VIN = VCP = 5.5V
1
2
VPWR = VIN = VCP = 11V
1
2
1.2
1.6
A
1
μA
ILIM_LX
0.8
LX Leakage Current
VLX = 76V
Line Regulation
2.9V ≤ VPWR ≤ 11V, VPWR = VIN,
ILOAD = 4.5mA
Load Regulation
0 ≤ ILOAD ≤ 4.5mA
2
90
1.2201
ILX = 100mA
kHz
0.2
%
1
%
_______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
(VIN = VPWR = 3.3V. VSHDN = 3.3V. CIN = CPWR = 10μF. CCP = 10nF, VCNTRL = VIN. VRLIM = 0V. VPGND = VSGND = 0V. VBIAS = 40V.
APD = unconnected. CLAMP = unconnected. ILIM = unconnected, MOUT = unconnected. TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
Soft-Start Duration
Soft-Start Steps
(0.25 x ILIM_LX) to ILIM_LX
TYP
MAX
UNITS
8
ms
32
Steps
1.25
V
CONTROL INPUT (CNTRL)
Maximum Control Input-Voltage
Range
FB set point is regulated to VCNTRL
CURRENT MONITOR
Bias Voltage Range
Bias Quiescent Current
VBIAS
IBIAS
Voltage Drop
VDROP
Dynamic Output Resistance at
MOUT
RMOUT
MOUT Output Leakage
Output Clamp Voltage
76
V
IAPD = 500nA
10
100
μA
IAPD = 2mA
3.2
mA
1
V
IAPD = 2mA, VDROP = VBIAS - VAPD
IAPD = 500nA
1
GΩ
IAPD = 2.5mA
890
MΩ
1
nA
APD is unconnected
VMOUT VCLAMP
Forward diode current = 1mA
Output Clamp Leakage Current
VBIAS = VCLAMP = 76V
Output-Voltage Range
10V ≤ VBIAS ≤ 76V, 0 ≤ IAPD ≤ 1mA, clamp
is unconnected
Current Gain
VMOUT
IMOUT/IAPD
Power-Supply Rejection Ratio
APD Input Current Limit
PSRR
ILIM_APD
Power-Up Settling Time
tS
V
nA
V
0.1
IAPD = 2mA
0.0965
0.1
0.1035
IAPD = 500nA
-1000
+300
+1500
IAPD = 5μA to
1mA
-250
+24
+250
3.15
3.75
4.35
mA
5
mA
VAPD = 35V, RLIM = 3.3kΩ
IMOUT settles to within
0.1%, 10nF connected
from APD to ground
0.95
VBIAS 1V
IAPD = 500nA
(ΔIMOUT/IMOUT)/ΔVBIAS,
VBIAS = 10V to 76V
(Note 3)
0.73
1
12.45kΩ ≥ RLIM ≥ 2.5kΩ
Current-Limit Adjustment Range
0.5
ppm/V
1
IAPD = 500nA
7.5
ms
IAPD = 2.5mA
90
μs
LOGIC INPUTS/OUTPUTS
SHDN Input-Voltage Low
VIL
SHDN Input-Voltage High
VIH
ILIM Output-Voltage Low
VOL
ILIM = 2mA
0.3
V
ILIM Output Leakage Current
IOH
VILIM = 11V
1
μA
0.8
2.4
V
V
THERMAL PROTECTION
Thermal Shutdown
Temperature rising
Thermal Shutdown Hysteresis
+160
°C
10
°C
Note 2: All minimum/maximum parameters are tested at TA = +125°C. Limits over temperature are guaranteed by design.
Note 3: Guaranteed by design and not production tested.
_______________________________________________________________________________________
3
MAX15061
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VPWR = VIN = 3.3V, VOUT = 70V, circuit of Figure 3 (Figure 4 for VIN > 5.5V), unless otherwise noted.)
60
50
40
VOUT = 55V
30
VOUT = 70V
20
EFFICIENCY (%)
50
EFFICIENCY (%)
50
40
VOUT = 55V
30
VOUT = 70V
10
3
VIN = 5V
VOUT = 70V
0
0
2
30
VIN = 5V
0
1
VIN = 8V
VIN = 3.3V
10
10
VIN = 3.3V
0
40
20
20
4
1
0
2
3
1
0
4
2
3
4
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
MINIMUM STARTUP VOLTAGE
vs. LOAD CURRENT
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
2.53
2.52
2.51
2.50
TA = +25°C
1.4
1.2
TA = +85°C
1.0
0.8
0.6
TA = +125°C
0.4
2.49
0.2
VFB = 1.4V
0
2.48
1
0
2
3
4
0
LOAD CURRENT (mA)
1
2
3
4
5
6
7
8
60
XMAX15061 toc06
1.6
SUPPLY CURRENT (mA)
2.54
TA = -40°C
1.8
NO-LOAD SUPPLY CURRENT (mA)
2.0
MAX15061 toc04
2.55
MAX15061 toc05
EFFICIENCY (%)
VOUT = 30V
60
70
MAX15061 toc02
MAX15061 toc01
VOUT = 30V
60
EFFICIENCY vs. LOAD CURRENT
EFFICIENCY vs. LOAD CURRENT
70
MAX15061 toc03
EFFICIENCY vs. LOAD CURRENT
70
MINIMUM STARTUP VOLTAGE (V)
MAX15061
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
50
TA = +85°C
40
TA = +25°C
30
TA = -40°C
20
10
0
9 10 11
3
4
5
EXITING SHUTDOWN
6
7
8
9
10
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
ENTERING SHUTDOWN
MAX15061 toc07
MAX15061 toc08
70V
OUTPUT VOLTAGE
50V/div
3V
VOUT
50V/div
3V
INDUCTOR CURRENT
500mA/div
IL
500mA/div
0mA
0mA
IOUT = 1mA
0V
1ms/div
4
SHUTDOWN VOLTAGE
2V/div
VSHDN
2V/div
0V
ILOAD = 1mA
4ms/div
_______________________________________________________________________________________
11
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX15061
Typical Operating Characteristics (continued)
(VPWR = VIN = 3.3V, VOUT = 70V, circuit of Figure 3 (Figure 4 for VIN > 5.5V), unless otherwise noted.)
LIGHT-LOAD SWITCHING
WAVEFORM WITH RC FILTER
HEAVY-LOAD SWITCHING
WAVEFORM WITH RC FILTER
MAX15061 toc09
MAX15061 toc10
IOUT = 0.1mA, VBIAS = 70V
IOUT = 4mA, VBIAS = 70V
VBIAS
AC-COUPLED
1mV/div
VBIAS
AC-COUPLED
1mV/div
VLX
50V/div
VLX
50V/div
0V
0V
IL
500mA/div
0mA
IL
500mA/div
0mA
1μs/div
1μs/div
LX LEAKAGE CURRENT
vs. TEMPERATURE
LINE-TRANSIENT RESPONSE
MAX15061 toc12
200
VIN
2V/div
3.3V
VOUT
AC-COUPLED
200mV/div
ILOAD
5mA/div
0mA
VOUT
AC-COUPLED
100mV/div
VOUT = 70V
IOUT = 1mA
tRISE = 50μs
VOUT = 70V
VIN = 3.3V
160
140
120
100
80
60
40
20
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
100ms/div
100ms/div
CURRENT INTO
LX PIN
180
LX LEAKAGE CURRENT (nA)
MAX15061 toc11
MAX15061 toc13
LOAD-TRANSIENT RESPONSE
TEMPERATURE (°C)
MAXIMUM LOAD CURRENT
vs. INPUT VOLTAGE
69.4
69.2
69.0
68.8
68.6
68.4
68.2
100
90
80
70
A
60
B
50
C
40
E
20
1
2
3
LOAD CURRENT (mA)
4
5
IAPD = 500nA
0.1
F
A: VOUT = 30V, B: VOUT = 35V, C: VOUT = 45V,
D: VOUT = 55V, E: VOUT = 60V, F: VOUT = 72V
0
0
D
IAPD = 2mA
1
30
10
68.0
10
BIAS CURRENT (mA)
OUTPUT VOLTAGE (V)
69.6
110
MAX15061 toc15
69.8
MAXIMUM LOAD CURRENT (mA)
MAX15061 toc14
70.0
BIAS CURRENT
vs. BIAS VOLTAGE
MAX15061 toc16
LOAD REGULATION
3
4
5
6
7
8
INPUT VOLTAGE (V)
9
10
11
0.01
0
10
20
30
40
50
60
70
80
BIAS VOLTAGE (V)
_______________________________________________________________________________________
5
Typical Operating Characteristics (continued)
(VPWR = VIN = 3.3V, VOUT = 70V, circuit of Figure 3 (Figure 4 for VIN > 5.5V), unless otherwise noted.)
0.1
3
1
0.1
VBIAS = 70V
4
2
GAIN ERROR (%)
1
5
MAX15061 toc18
IAPD = 2mA
BIAS CURRENT (mA)
VBIAS = 70V
GAIN ERROR
vs. APD CURRENT
10
MAX15061 toc17
10
BIAS CURRENT
vs. TEMPERATURE
IAPD = 500nA
MAX15061 toc19
BIAS CURRENT
vs. APD CURRENT
BIAS CURRENT (mA)
1
0
-1
-2
-3
-4
0.01
0.001
0.01
0.1
1
-5
-40 -25 -10 5 20 35 50 65 80 95 110 125
10
APD CURRENT (mA)
IAPD = 500μA
0.40
GAIN ERROR (%)
IAPD = 50μA
-1.0
IAPD = 5μA
0.60
0
IAPD = 5μA
1000
0.80
MAX15061 toc20
IAPD = 2mA
100
10,000
GAIN ERROR
vs. BIAS VOLTAGE
0.5
-0.5
10
IAPD (μA)
GAIN ERROR
vs. TEMPERATURE
1.0
1
0.1
TEMPERATURE (°C)
IAPD = 500nA
-1.5
MAX15061 toc21
0.01
0.0001
GAIN ERROR (%)
MAX15061
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
IAPD = 50μA
0.20
0
-0.20
IAPD = 500nA
-0.40
-2.0
IAPD = 500μA
-0.60
-2.5
VBIAS = 70V
IAPD = 2mA
-0.80
-3.0
10
-40 -25 -10 5 20 35 50 65 80 95 110 125
20
30
40
50
60
70
80
BIAS VOLTAGE (V)
TEMPERATURE (°C)
APD TRANSIENT RESPONSE
STARTUP DELAY
MAX15061 toc22
MAX15061 toc23
VAPD
AC-COUPLED
70V
2V/div
VBIAS
20V/div
IAPD
2.5mA/div
3V
0mA
IMOUT
0.25mA/div
0mA
IAPD = 500nA
IMOUT
20nA/div
0nA
20μs/div
6
200μs/div
_______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
STARTUP DELAY
STARTUP DELAY
MAX15061 toc25
MAX15061 toc24
VAPD
20V/div
VAPD
2V/div
3V
0V
IMOUT
50μA/div
IAPD = 2mA
IMOUT
20nA/div
IAPD = 500nA
VBIAS = 5V
0nA
0nA
100μs/div
100μs/div
STARTUP DELAY
SHORT-CIRCUIT RESPONSE
MAX15061 toc26
MAX15061 toc27
ILIM
2V/div
VBIAS
2V/div
0V
0V
IBIAS
2mA/div
IMOUT
50μA/div
IAPD = 2mA
VBIAS = 5V
0nA
40μs/div
40ms/div
VOLTAGE DROP
vs. APD CURRENT
SWITCHING FREQUENCY
vs. TEMPERATURE
1.00
TA = +25°C
TA = -40°C
0.80
0.60
0.40
0.20
TA = +85°C
TA = +125°C
1
100
0mA
MAX15061 toc29
1.20
500
480
SWITCHING FREQUENCY (kHz)
MAX15061 toc28
1.40
VBIAS - VAPD (V)
VBIAS = 70V
TA = +85°C
RLIM = 2kΩ
460
440
420
400
380
360
340
320
300
0
0.1
10
IAPD (μA)
1000
10,000
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
_______________________________________________________________________________________
7
MAX15061
Typical Operating Characteristics (continued)
(VPWR = VIN = 3.3V, VOUT = 70V, circuit of Figure 3 (Figure 4 for VIN > 5.5V), unless otherwise noted.)
Typical Operating Characteristics (continued)
(VPWR = VIN = 3.3V, VOUT = 70V, circuit of Figure 3 (Figure 4 for VIN > 5.5V), unless otherwise noted.)
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
SWITCHING FREQUENCY AND
DUTY CYCLE vs. LOAD CURRENT
460
440
420
400
380
360
340
415
DUTY CYCLE
40
405
30
400
SWITCHING FREQUENCY
395
20
390
385
300
380
10
MEASURED AT CN
2
4
6
8
10
0
0
12
1
2
3
4
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
FB SET-POINT VARIATION
vs. TEMPERATURE
APD OUTPUT RIPPLE VOLTAGE
MAX15061 toc33
MAX15061 toc32
1.277
1.267
VIN = 2.9V
VIN = 5.5V
1.247
1.237
50
410
320
1.257
60
DUTY CYCLE
SWITCHING FREQUENCY (kHz)
480
MAX15061 toc31
420
SWITCHING FREQUENCY (kHz)
MAX15061 toc30
500
FB SET-POINT VOLTAGE VARIATION (V)
MAX15061
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
VAPD
AC-COUPLED, 55V
200μV/div
FB RISING
VIN = 2.9V
VIN = 5.5V
1.227
FB FALLING
1.217
1.207
-40 -25 -10 5 20 35 50 65 80 95 110 125
2μs/div
TEMPERATURE (°C)
APD OUTPUT RIPPLE VOLTAGE
APD OUTPUT RIPPLE VOLTAGE
MAX15061 toc34
MAX15061 toc35
VAPD
AC-COUPLED, 55V
100μV/div
0.1μF CAPACITOR CONNECTED
FROM APD TO GND.
2μs/div
8
VAPD
AC-COUPLED, 70V
500μV/div
0.1μF CAPACITOR CONNECTED
FROM APD TO GND.
2μs/div
_______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
PIN
NAME
FUNCTION
1
PWR
Boost Converter Input Voltage. PWR powers the switch driver and charge pump. Bypass PWR to PGND with a
ceramic capacitor of 1μF minimum value.
2
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.
3
CN
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.
4
IN
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.
5
SGND
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.
6
FB
Feedback Regulation Input. Connect FB to the center tap of a resistive voltage-divider from the output (VOUT)
to SGND to set the output voltage. The FB voltage regulates to 1.245V (typ) when VCNTRL is above 1.5V (typ)
and to VCNTRL voltage when VCNTRL is below 1.245V (typ).
7
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.
8
ILIM
Open-Drain Current-Limit Indicator. ILIM asserts low when the APD current limit has been exceeded.
9
RLIM
Current-Limit Resistor Connection. Connect a resistor from RLIM to SGND to program the APD current-limit
threshold.
10
MOUT
Current-Monitor Output. MOUT sources a current 1/10 of IAPD.
11
CLAMP
12
APD
Reference Current Output. APD provides the source current to the cathode of the photodiode.
13
BIAS
Bias Voltage Input. Connect BIAS to the boost converter output (VOUT) either directly or through a lowpass
filter for ripple attenuation. BIAS provides the voltage bias for the current monitor and is the current source for
APD.
14
SHDN
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 VSHDN is not greater
than the input voltage, VIN.
15
PGND
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.
16
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.
—
EP
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.
Clamp Voltage Input. CLAMP is the external potential used for voltage clamping of MOUT.
_______________________________________________________________________________________
9
MAX15061
Pin Description
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX15061
Functional Diagram
PWR
-A
FB
VREF
MUX
CNTRL
OUTPUT ERROR AND CURRENT
COMPARATOR
+A
LX
-C
SGND
+C
PEAK CURRENT-LIMIT
COMPARATOR
SOFTSTART
SWITCH
CONTROL
LOGIC
80V
DMOS
PGND
REFERENCE
COMPARATOR
VREF
SWITCH
CURRENT
SENSE
CLAMP
CN
CP
CHARGE
PUMP
(DOUBLER)
THERMAL
SHUTDOWN
1x
VREF
MAX15061
CURRENT
MONITOR
MOUT
CURRENTLIMIT
ADJUSTMENT
RLIM
CURRENT
LIMIT
APD
BIAS AND
REFERENCE
IN
UVLO
10x
CLK
ILIM
OSCILLATOR
400kHz
SHDN
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 MAX15061 operates in discontinuous mode in
order to reduce the switching noise caused by reversevoltage recovery charge of the rectifier diode. Other
continuous mode boost converters generate large voltage spikes at the output when the LX switch turns on
10
BIAS
because there is a conduction path between the output, diode, and switch to ground during the time needed 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.
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.
______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
The MAX15061 also features a shutdown logic input to
disable the device and reduce its standby current to
2μA (max).
Fixed-Frequency PWM Controller
The heart of the MAX15061 current-mode PWM controller 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 configuration approaches ideal cycle-by-cycle control over the
output voltage since there is no conventional error
amplifier in the feedback path.
The device operates in PWM mode using a fixed-frequency, current-mode operation. The current-mode frequency loop regulates the peak inductor current as a
function of the output error signal.
The current-mode PWM controller is intended for discontinuous 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 chargepump circuitry and an external 10nF ceramic capacitor
connected between CP and CN double the available internal 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.
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.
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.
Clamping the Monitor
Output Voltage (CLAMP)
CLAMP provides a means for diode clamping the voltage at MOUT; thus, V MOUT is limited to (V CLAMP +
0.6V). CLAMP can be connected to either an external
supply or BIAS. CLAMP can be left unconnected if voltage clamping is not required.
Adjusting the Boost Converter
Output Voltage (FB/CNTRL)
The boost converter output voltage can be set by connecting FB to a resistor-divider from VOUT to ground.
The set-point feedback reference is the 1.245 (typ)
internal reference voltage when VCNTRL > 1.5V and is
equal to the CNTRL voltage when VCNTRL < 1.25V.
To change the converter output on the fly, apply a voltage lower than 1.25V (typ) to the CNTRL input and
adjust the CNTRL voltage, which is the reference input
of the error amplifier when VCNTRL < 1.25V (see the
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 variation 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.
Shutdown (SHDN)
The MAX15061 features an active-low shutdown input
(SHDN). Pull SHDN low to enter shutdown. During shutdown, 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.
______________________________________________________________________________________
11
MAX15061
The MAX15061 includes a versatile current monitor
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 provides an output current accurately proportional to the
APD current at MOUT.
MAX15061
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
VOUT
output current in amperes, L is the inductor value in
microhenrys, and η is the efficiency of the boost converter (see the Typical Operating Characteristics).
Determining the Inductor Value
R2
FB
MAX15061
R1
Three key inductor parameters must be specified for
operation with the MAX15061: inductance value (L),
inductor saturation current (ISAT), and DC resistance
(DCR). In general, the inductor should have a saturation
current rating greater than the maximum switch peak
current-limit value (ILIM-LX = 1.6A). Choose an inductor
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
LMIN [μH] =
2 × TS × IOUT × (VOUT − VIN_MIN )
Design Procedure
Setting the Output Voltage
Set the MAX15061 output voltage by connecting a resistive divider from the output to FB to SGND (Figure 1).
Select R1 (FB to SGND resistor) between 200kΩ and
400kΩ. Calculate R2 (VOUT to FB resistor) using the following equation:
⎡⎛ V
⎞ ⎤
R2 = R1 ⎢⎜ OUT ⎟ − 1⎥
⎣⎝ VREF ⎠ ⎦
where VOUT can range from (VIN + 1V) to 76V and VREF
= 1.245V or VCNTRL depending on the VCNTRL value.
For VCNTRL > 1.5V, the internal 1.245V (typ) reference
voltage is used as the feedback set point (V REF =
1.245V) and for VCNTRL < 1.25V, VREF = VCNTRL.
Determining Peak Inductor Current
If the boost converter remains in the discontinuous
mode of operation, then the approximate peak inductor
current, ILPEAK (in amperes), is represented by the formula below:
ILPEAK =
2 × TS × (VOUT − VIN_MIN ) × IOUT_MAX
η×L
where T S is the switching period in microseconds,
VOUT is the output voltage in volts, VIN_MIN is the minimum input voltage in volts, IOUT_MAX is the maximum
12
2
η × ILIM-LX
where V IN_MIN , V OUT (both in volts), and I OUT (in
amperes) are typical values (so that efficiency is optimum for typical conditions), TS (in microseconds) is the
period, η is the efficiency, and I LIM_LX is the peak
switch current in amperes (see the Electrical
Characteristics table).
Calculate the optimum value of L (LOPTIMUM) to ensure
the full output power without reaching the boundary
between continuous conduction mode (CCM) and DCM
using the following formula:
L
[μH]
LOPTIMUM [μH] = MAX
2.25
where LMAX [μH] =
2
VIN_MIN
(VOUT − VIN_MIN ) × TS × η
2
2 × IOUT × VOUT
For a design in which VIN = 3.3V, VOUT = 70V, IOUT=
3mA, η = 45%, ILIM-LX = 1.3A, and TS = 2.5μs: LMIN =
1.3μH and LMAX = 23μH.
For a worse-case scenario in which VIN = 2.9V, VOUT =
70V, IOUT= 4mA, η = 43%, ILIM-LX= 1.3A, and TS =
2.5μs: LMIN = 1.8μH and LMAX = 15μH.
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.
______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
For very low output ripple applications, the output of the
boost converter can be followed by an RC filter to further
reduce the ripple. Figure 2 shows a 100Ω (RF), 0.1μF
(CF) filter used to reduce the switching output ripple to
1mVP-P with a 0.1mA load or 2mVP-P with a 4mA load.
The output-voltage regulation resistor-divider must remain
connected to the diode and output capacitor node.
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 capacitor 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:
COUT[μF] =
Input Capacitor Selection
Bypass PWR to PGND with a 1μF (min) ceramic capacitor and bypass IN to PGND with a 1μF (min) ceramic
capacitor. Depending on the supply source impedance, 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 layout 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 electrolytic 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:
⎡
ILPEAK x LOPTIMUM ⎤
⎢ TS −
⎥
(VOUT − VIN_MIN ) ⎥⎦
⎢⎣
0.5 x ΔVOUT
ESR [m Ω ] =
IOUT
IOUT
0.5 x ΔVOUT
CIN[μF] =
⎡
VOUT x IOUT
ILPEAK x LOPTIMUM x VOUT ⎤
⎢ TS −
⎥
η x VIN_MIN x 0.5 x ΔVIN ⎢⎣
VIN_MIN (VOUT − VIN_MIN ) ⎥⎦
0.5 x ΔVIN x η x VIN_MIN
ESR [m Ω ] =
VOUT x IOUT
L1
CIN
VIN = 2.7V TO 5.5V
PWR
RF
100Ω
D1
IN
VOUT
LX
CNTRL
R2
SHDN
MAX15061
COUT1
FB
CF
0.1μF
CP
CPWR
R1
CCP
CN
BIAS
PGND
SGND
Figure 2. Typical Operating Circuit with RC Filter
______________________________________________________________________________________
13
MAX15061
Diode Selection
The MAX15061’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommended 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
voltage must be greater than VOUT, the output voltage
of the boost converter.
MAX15061
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
Determining Monitor Current Limit
Calculate the value of the monitor current-limit resistor,
RLIM, for a given APD current limit, ILIMIT, using the following equation:
RLIM = 10 ×
1.245V
ILIMIT (mA)
The RLIM resistor, RLIM, ranges from 12.45kΩ to 2.5Ω
for APD currents from 1mA to 5mA.
Applications Information
Using APD or PIN Photodiodes
in Fiber Applications
When using the MAX15061 to monitor APD or PIN photodiode currents in fiber applications, several issues
must be addressed. In applications where the photodiode must be fully depleted, keep track of voltages budgeted 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.
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 referenced as desired with either a resistor to ground or a
transimpedance amplifier. Take care to ensure that output voltage excursions do not interfere with the required
margin between BIAS and MOUT. In many fiber applications, MOUT is connected directly to an ADC that operates 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
14
protection is less critical when MOUT is connected
directly to subsequent transimpedance amplifiers (linear
or logarithmic) that have low-impedance, near-groundreferenced 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 conditions, but grows with temperature.
To maintain low levels of wideband noise, lowpass filtering 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.
In some applications where pilot tones are used to identify 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.
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 capacitance, trace resistance, and radiated noise. Ensure that
the feedback connection to FB is short and direct.
Route high-speed switching nodes away from the sensitive 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 capacitors. Refer to the MAX15061 evaluation kit data sheet
for a layout example.
______________________________________________________________________________________
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
MAX15061
L1
4.7μH
D1
VOUT (70V MAX)
VIN
COUT
0.1μF
CPWR
1μF
PWR
RADJ
CF
0.1μF
LX
CNTRL
R2
348kΩ
RF
100Ω
R1
6.34kΩ
PGND
IN
CIN
1μF
BIAS
FB
MAX15061
SHDN
CP
CCP
10nF
GPIO
ILIM
GPIO
VDD
CN
VDD
CLAMP
RLIM
RLIM
2.87kΩ
SGND
μC
APD MOUT
ADC
APD
RMOUT
10kΩ
DAC
CMOUT
(OPTIONAL)
Figure 3. Typical Operating Circuit for VIN = 2.7V to 5.5V
______________________________________________________________________________________
15
MAX15061
80V, 300mW Boost Converter and Current
Monitor for APD Bias Applications
L1
4.7μH
VIN = 5.5V TO 11V
D1
VOUT (70V MAX)
COUT
0.1μF
CPWR
1μF
PWR
CF
0.1μF
LX
CNTRL
R2
348kΩ
RF
100Ω
R1
634kΩ
PGND
IN
CIN
1μF
BIAS
FB
CP
MAX15061
SHDN
GPIO
ILIM
CN
GPIO
VDD
VDD
CLAMP
RLIM
RLIM
2.87kΩ
SGND
μC
APD MOUT
ADC
APD
RMOUT
10kΩ
DAC
CMOUT
(OPTIONAL)
Figure 4. Typical Operating Circuit for VIN = 5.5V to 11V
Package Information
Chip Information
PROCESS: BiCMOS
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 drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
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
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