PM8800 STMicroelectronics, PM8800 Datasheet
PM8800
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PM8800 Summary of contents
Page 1
... The integrated switching regulator has been designed to work with power either form the Ethernet cable connection or from an external power source such as AC adapter. The DC-DC section of the PM8800A features a programmable oscillator frequency, soft-start, slope compensation and embeds a voltage output error amplifier allowing use in both isolated and non isolated configuration ...
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... Under voltage lock-out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.4 In rush current limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.5 Continuos current limitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.6 HV regulator startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.7 Power good indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 6 PWM section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 6.1 Error amplifier and loop compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 6.2 Oscillator and sync capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.3 Soft start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 6.4 PWM comparator / slope compensation . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.5 Current limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.6 Leading edge blanking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6.7 Thermal protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2/35 PM8800A ...
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... PM8800A 7 Auxiliary sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 8.1 HTSSOP16 mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Contents 3/35 ...
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... Typical application circuit and block diagram 1 Typical application circuit and block diagram 1.1 Application circuits Figure 1. Simplified application schematic for powered devicesing PM8800A in isolated configuration Figure 2. Simplified application schematic for powered device using PM8800A in non-isolated buck configuration 4/35 VIN AUXII VCC GD AUXI_IRL COMP ...
Page 5
... Logic + VCC UVLO VCC Thermal threshold 1.5V Protection + - 1. VCC Driver SET 45µA CLR + PWM PWM logic - DC/DC Enable Cycle by cycle over current protection 80% duty cycle limit (PM8800A) Leading Edge Blanking + OC1 Hiccup on OC2 or - persistent OC1 + OC2 - VCC 30uA nPGD 2V GND GD 5/35 ...
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... See A resistance between this pin and VSS will set the level of inrush current limit. 16 AGND VFB 15 14 COMP nPGD 11 VCC GND Function Section 6 for detail. Section 7 for detail. Section 7 for details. PM8800A ...
Page 7
... Pins description and connection diagrams DC current limit. A resistor between DCCL and VSS will set the current limit for the interface section of the PM8800A. It can be set to exceed the IEEE802.3af current limit. Leave the pin open for standard IEEE 802.3af applications. System low potential input. ...
Page 8
... Max thermal resistance junction to ambient thJA T Maximum junction temperature MAX T Storage temperature range STG T Junction temperature range J T Operative temperature range A 1. Package mounted on 4 layers 35 micron demoboard 8/35 Parameter (1) PM8800A Value Unit 50 °C/W 150 °C -40 to 150 °C -40 to 125 °C - °C ...
Page 9
... PM8800A 3 Electrical specifications 3.1 Absolute maximum ratings Table 4. Absolute maximum ratings VIN, GND to VSS AUXI_IRL to VSS DCCL, RCLASS to VSS AUXII to AGND COMP AGND VFB, RT AGND VCC AGND nPGD to AGND GND to AGND Note: Absolute maximum ratings are limits beyond which damage to the device may occur. ...
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... VCC = rising IN V falling IN V > < V < 1.5 V < V < kΩ AUXI_IRL R = From 15.4 kΩ kΩ DCLL PM8800A Min Typ Max Unit (1) 1.5 V (1) (1) 23.5 24.5 25.5 kΩ (1) (1) 10.5 11.5 12.5 V 1.40 V (1) (1) 21 ...
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... PM8800A Table 5. Electrical characteristics - interface section (continued VCC = open °C unless otherwise specified Symbol Parameter Power good indication Hot-swap V DS Hysteresis Hot-swap V required GS for power good nPGD current source nPGD pull down nPGD resistance nPGD threshold Auxiliary power ...
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... After soft start Guaranteed by design Guaranteed by design Guaranteed by design I = 100 mA; GD guaranteed by design I = -100 3.3 nF LOAD C = 3.3 nF LOAD C = 3.3 nF; LOAD guaranteed by design PM8800A Min Typ Max Unit (1) (1) 85 100 115 kHz (1) (1) 210 240 270 kHz (1) (1) 385 440 495 kHz 2 ...
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... CC dropout Note: 1 These values applies over the full operating temperarure range. 2 Device thermal limitations could limit useful operating range. 3 The V regulator is intended for internal use only as bias supply of PM8800A; any CC additional external V Test conditions C = 3.3 nF; LOAD Guaranteed by design st 1 level; Inrush phase only; ...
Page 14
... State diagram of the PM8800A interface depending on the input voltage Detection 1.5V For input voltages in the range 1.5 to 11.5 V, PM8800A exposes a 24.5 kΩ resistance. After detection is over, the internal resistor is disabled and the external classification resistor is presented. When classification is over, the external resistor is disconnected and the PM8800A wait for the input voltage to overpass the UVLO voltage ...
Page 15
... PM8800A PM8800A can work with power either from PoE networks or from auxiliary sources - like AC adapters -. Alternative sources are present in PoE appliances where devices can work also outside the context of the PoE networks or to ensure normal operation even if PoE becomes unavailable. PM8800A limits the number of external components to handle the coexistence of both PoE and auxiliary supplies ...
Page 16
... The value of the integrated detection resistance has been selected taking into account also the diode bridges typical voltage drop. During detection, most of the circuits inside the PM8800A are disabled to minimize the offset current. Figure 7. ...
Page 17
... V and 20.5 V for a maximum duration and senses the current flowing through the cable to determine the PD's class. The relevant thresholds in PM8800A are 11.5 V and 23 V, with a turn off hysteresis of 1 support the classification function, an equivalent programmable constant current generator has been implemented. The following figure depicts a principle schematic of the classification circuit ...
Page 18
... The IEEE 802.3af standard sets a maximum turn-on voltage (42 V) and the minimum turn- off voltage (30 V) for the PDs and indicates normal voltage drops across the Ethernet cable. The PM8800A implements the UVLO mechanism by setting 2 internal thresholds on the voltage across the VIN-VSS pins; one is to activate the hot-swap ( switch off the hot-swap MOSFET upon detection of a supply voltage drop (V from normal operating conditions ...
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... The formulae to select the desired inrush current is the following: 11200 [ ] R kΩ = ----------------------- - [ IRL I mA IRL The PM8800A useful programming range for the inrush current limitation is between 140 mA and 440 mA. Practical resistor value ranges between 25 kΩ and 82 kΩ. Figure 10. Inrush current limit vs R 15V 30V ] IRL PD interface VIN-VSS 19/35 ...
Page 20
... UVLO hysteresis ( order to avoid hiccup turn on. 5.5 Continuos current limitation PM8800A provide a default continuos current limitation of 440 mA. This is achieved by leaving the pin DCCDL floating. A different DC current limit can be set by connecting a resistor between DCCL and VSS whose value can be obtained by the following equation: ...
Page 21
... This limitation is active after nPGD set and when the PD is supplied through the PoE or in the Front connection (see The PM8800A useful programming range for the current limitation is between 150 mA and 800 mA. Practical resistor value ranges between 15 kΩ and 75 kΩ. ...
Page 22
... Power good indication The PM8800A embeds a power good circuit that is used to indicate that PWM input capacitors are fully charged and that the switching regulator can start operation. The power good circuit monitors the status of the internal hot-swap MOSFET and nPGD, an active low ...
Page 23
... PWM section 6.1 Error amplifier and loop compensation The PM8800A addresses both isolated and non-isolated configuration by embedding a wide band high gain error amplifier. In non-isolated topology, the voltage to be regulated is connected to the FB pin - the inverting input of the EA - through a resistor divider. The non inverting input of the EA is set to a fixed reference value of 1.25 V. The output of the error amplifier is connected to the COMP pin which is pulled up internally with a 2.5 kΩ ...
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... The PWM switching frequency is equal to the programmed oscillator frequency. 24/35 Figure 14 for details. The output voltage is given by the R ⎞ 2 ------ - ⎠ ⎛ ⎞ 125 1 + ------------------------------------- - ⎝ ⎠ 3kΩ kΩ 900 800 700 600 500 400 300 200 100 0 0 100 RT [kOhm] 200 300 400 PM8800A and the OSC ...
Page 25
... When synchronized the PWM frequency is equal to the external clock reference. 6.3 Soft start The soft-start feature of the PM8800A allows the load voltage to ramp- safe and controlled manner. This is achieved µA internal current source charging an external C capacitor connected to the SS pin, which progressively increases the duty cycle of the ss PWM pulse, since the reference of the error amplifier is clamped with this value ...
Page 26
... COMP pin voltage drops below approximately 0.7 V. For duty cycles greater than 50 %, current mode control loops are subject to sub-harmonic oscillation. The PM8800A fixes the maximum duty dycle and implements a slope compensation technique consisting on adding an additional fixed slope voltage ramp to the signal at the CS pin. This is achieved by injecting a 45 µ ...
Page 27
... PM8800A Figure 17. Short circuit on the output Ch1 = 5Vout, Ch2 = SoftStart, Ch3 = VSS - GND, Ch4 = I input When a severe over current occurs, like a short circuit of an internal power component, and 0.7 V level is reached on CS, the gate driver is instantaneously shut down and a fast hiccup cycle is performed. When the 10 µA sink current fully discharges the SS capacitor, a new soft-start procedure is performed ...
Page 28
... MOSFET. 6.7 Thermal protection PM8800A has a two level thermal protection referred to the internal junction temperature. First limit is set to 130 °C and limits the current into the hot-swap MOSFET to 140 mA every time the voltage difference between VSS and GND is higher than 3 V. ...
Page 29
... As depicted in the following figure there are two available options for connecting auxiliary sources to the PM8800A. One possibility consists in diode O-ring the auxiliary source into the PM8800A PoE pins (VIN and VSS) referred to "Option I ". In the second alternative, referred to "Option II" the external supply voltage is diode ORed into the PWM section of the device ...
Page 30
... If a prevalent AUXII is detected the PD interface is switched off, the hot swap MOSFET is opened regardless the PoE voltage level. 30/ – D ≥ 70µA resistor and forcing a current into the pin greater AUXII · – V – 1.1 D ≥ 100µA AUXII PM8800A ...
Page 31
... DC/DC converter will be drawn from the source that has been applied first. In case of very low auxiliary voltage (i.e. lower than recommended to supply VCC directly with the auxiliary voltage through a bypass diode, in order to assure a proper operation of the pwm section of PM8800A. Figure 20. Switch over between 48 V PoE and 12 V AUXII auxiliary adapter Ch2 ...
Page 32
... These packages have a lead-free second level interconnect. The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK trademark. ECOPACK specifications are available at: www.st.com. 32/35 PM8800A ® ...
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... PM8800A 8.1 HTSSOP16 mechanical data Figure 21. HTSSOP16 mechanical data and package dimensions mm DIM. min typ 0.80 1.0 b 0.19 c 0.09 D 4.90 5.00 D1 3.00 E 6.20 6.40 E1 4.30 4.40 E2 3.00 e 0.65 L 0.45 0. aaa inch max min typ max 1.20 0.047 0.15 0.006 1.05 0.032 0.039 0.041 0.30 0.007 0.012 0.20 0.004 0.008 5.10 0.193 0.197 0.201 0.118 6.60 0.244 ...
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... Revision history 9 Revision history Table 8. Document revision history Date 17-Sep-2007 20-Feb-2008 34/35 Revision 1 Initial release 2 Content reworked in order to improve readability PM8800A Changes ...
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... PM8800A Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. ...