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PDF RT8550 Data sheet ( Hoja de datos )
| Número de pieza | RT8550 | |
| Descripción | 76V Boost DC/DC Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT8550
76V Boost DC/DC Converter with APD Current Monitor
General Description
The RT8550 is a high performance, low noise Boost DC/
DC converter with an integrated internal switch and an
avalanche photodiodes (APD) current monitor. The
RT8550's input voltage ranges from 2.8V to 5.5V, and it
can support the output voltage up to 76V. When used in
optical receiver application to drive the high voltage APD
diode, the output voltage of the RT8550 can be further
doubled up by a typical voltage doubler circuit. The RT8550
adapts fixed frequency, current mode PWM control loop
to regulate the output voltage with fast transient response
and cycle-by-cycle current limit. With 400kHz switching
frequency, the RT8550 system board can be made compact
to achieve low system BOM cost. The soft-start function
and PWM loop compensation is also built-in internally to
save external soft-start capacitor and PWM loop
compensation components. The RT8550 features accurate
APD current monitoring output with 5:1 ratio at the MON
pin. A Resistor-adjustable APD current limit function
protects the APD diode from Boost output transients. The
protection features of the RT8550 include input under-
voltage lockout and over temperature protection. The
RT8550 is available in the small and WQFN-16L 3x3
package.
Features
Input Voltage Range : 2.8V to 5.5V
Up to 76V Output Voltage
400kHz Fixed Switching Frequency
Internal Compensation and Soft-Start
APD Current Monitor within ±5% Tolerance
5:1 Ratio outputs for APD Current Monitoring
Low Shutdown Current : <1μA
Programmable APD Current Limit
RoHS Compliant and Halogen Free
Applications
APD Bias Supply
PIN Diode Bias Supply
Optical Receivers and Modules
Fiber Optic Network Equipment
GPON Modules
Marking Information
21= : Product Code
21=YM
DNN
YMDNN : Date Code
Simplified Application Circuit
L1 D1
VIN VOUT
CIN
RT8550
VIN SW
COUT
R2
RLIM
SHDN
RLIM
MONIN
FB
CTRL
R1
SGND
PGND
MON
APD
APD
TIA
R3
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8550-02 December 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
RT8550
Parameter
Symbol
Test Conditions
Internal Switch On-Resistance
ISW = 100mA, VIN = 3.3V
Peak Switch Current Limit
SW Leakage Current
VSW = 76V
Line Regulation
VIN = 2.8V to 5.5V
Soft-Start Duration
(Note 5)
Control Input (CTRL)
CTRL Transition Threshold
VFB = VREF above this voltage
CTRL Input Bias Current
VCTRL = VFB_SET
Current Monitor
MONIN Voltage Range
VMONIN
MONIN Supply Current
Voltage Drop
MON Leakage Current
IMONIN
VDROP
IAPD = 1A, VMONIN = 76V
IAPD = 2.5mA, VMONIN = 76V
IAPD = 2mA, VMONIN = 76V,
VDROP = VMONIN VAPD
APD is Unconnected
MON Clamp Voltage
VMOUT
Current Gain
IMON
IAPD
Current Limit Adjustment Range
Forward Diode Current = 1mA
IAPD = 1A, 10V MONIN 76V
Boost Switch Off
IAPD = 2.5mA, 10V MONIN 76V
Boost Switch Off
RLIM = 4.7k
Logic I/O
High
SHDN Input Voltage
Low
VIH
VIL
Thermal Protection
Thermal Shutdown Threshold TSD
Temperature Rising
Min Typ Max
-- 1 2
0.58 0.7 0.88
-- -- 1
-- 0.5 1
-- 10 --
Unit
A
A
%
ms
-- 1.37 --
-- -- 500
V
nA
4.5 10 76
-- 1.3 --
-- 3 5
V
A
mA
-- 3.5 5
V
-- 1 300 nA
-- 2.3 --
V
0.18 0.2 0.22
mA/mA
0.18 0.2 0.22
-- 2 -- mA
2 -- --
-- -- 0.5
V
-- 150 --
°C
Note 1. Stresses beyond those listed “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 may
affect device reliability.
Note 2. θJA is measured at TA = 25 °C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
measured at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. Guarantee by design.
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8550-02 December 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
RT8550
For applications with output voltage less than 45V,
intermediate output VOUT can directly serve as the output.
Typically use a 0.47μF capacitor for output voltage less
than 25V and 1μF capacitor for output voltage between
25V and 45V. Either ceramic or solid tantalum capacitors
may be used for the input decoupling capacitor, which
should be placed as close as possible to the RT8550. A
1μF capacitor is sufficient for most applications.
Input Capacitor Selection
Low ESR ceramic capacitors are recommended for input
capacitor applications. Low ESR will effectively reduce
the input voltage ripple caused by switching operation. A
10μF capacitor is sufficient for most applications.
Nevertheless, this value can be decreased for lower output
current requirement. Another consideration is the voltage
rating of the input capacitor which must be greater than
the maximum input voltage.
APD Current Monitor
The power supply switching noise associated with a
switching power supply can interfere with the photodiode
DC measurement. To suppress this noise, a 0.1μF
capacitor is recommended at the MONIN pin. An additional
output low-pass filter, a 10k resistor and a 10nF capacitor
in parallel at the MON pin might limit the measurement
accuracy of low level signals. For applications requiring
fast current monitor response time, a RC low-pass filter
at the MONIN pin is used to replace the 0.1μF capacitor
at the APD pin to reduce the power supply noise and other
wide band noise.
APD Short Current Protection
The current limit of the current monitor is adjustable from
1mA to 4mA (typ). Connect RLIM to SGND to get a default
current-limit threshold of 4mA or connect a resistor from
RLIM to SGND to program the current-limit threshold below
the default setting. Calculate the value of the external
resistor, RLIM, for a given current limit using the following
Table 1 :
Table 1. APD Current Limit vs. RLIM Value (1%
Resistors)
RLIM (k) APD Current Limit (mA)
8.2 1
4.7 2
33
14
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TAis
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WQFN-16L 3x3 package, the thermal resistance, θJA, is
30°C/W on a standard JEDEC 51-7 four-layer thermal test
board. The maximum power dissipation at TA = 25°C can
be calculated by the following formula :
PD(MAX) = (125°C − 25°C) / (30°C/W) = 3.33W for
WQFN-16L 3x3 package
The maximum power dissipation depends on the operating
ambient temperature for fixed TJ(MAX) and thermal
resistance, θJA. The derating curve in Figure 1 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8550-02 December 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet RT8550.PDF ] | |
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