9-3320; Rev 1; 1/05 -48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection The MAX5938 is a hot-swap controller for -10V to -80V rails. The MAX5938 allows circuit line cards to be safely hot-plugged into a live backplane without causing a glitch on the power supply. It integrates an adjustable circuit-breaker function requiring no RSENSE.
MAX5938 -48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection ABSOLUTE MAXIMUM RATINGS VEE, VOUT, PGOOD, LP, STEP_MON to GND............................................+0.3V to -85V PGOOD to VOUT .....................................................-0.3V to +85V VOUT, LP, STEP_MON to VEE .................................-0.3V to +85V GATE to VEE ...........................................................-0.3V to +20V ON, OFF, OV, POL_SEL, CB_ADJ to VEE ................-0.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection (VEE = -10V to -80V, VIN = (GND - VEE), VSTEP_MON = VEE, RLP = 200Ω, VON = VOFF = 2V, VOV = VCB_ADJ = VEE, POL_SEL open, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VEE = -48V, TA = +25°C.
ELECTRICAL CHARACTERISTICS (continued) (VEE = -10V to -80V, VIN = (GND - VEE), VSTEP_MON = VEE, RLP = 200Ω, VON = VOFF = 2V, VOV = VCB_ADJ = VEE, POL_SEL open, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VEE = -48V, TA = +25°C.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS LOGIC AND FAULT MANAGEMENT Autoretry Delay 16 x tLP tRETRY PGOOD Assertion Delay Time (Note 6) 0.74 x VCB Hysteresis 0.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection GATE PULLDOWN CURRENT vs. GATE VOLTAGE 450 400 3.8 RETRY TIME (s) 350 300 250 200 CGATE = 0, CLOAD = 100µF 3.9 3.7 3.6 3.5 3.4 150 3.3 100 3.2 50 3.1 0 3.
Typical Operating Characteristics (continued) (VEE = -48V, GND = 0V, VIN = GND - VEE, POL_SEL = floating, all voltages are referenced to VEE, unless otherwise noted. TA = +25°C, unless otherwise noted.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection PIN NAME 1 GND Ground. The high supply connection for a negative rail hot-swap controller. 2, 10, 13, 15 N.C. No Connection. Not internally connected. Leave open. 3 OFF Off Control Input. Referenced to VEE. Drive OFF and ON above 1.25V (typ) to turn on the MAX5938. When the ON input low requirements are met and OFF falls below 1.25V (typ), the MAX5938 turns off. 4 ON On Control Input. Referenced to VEE.
MAX5938 -48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection GND RLOAD CLOAD PGOOD GND PG MAX5938 PGOOD LOGIC VOUT 10V REG AND 5V REG BANDGAP REF +10V +5V VSC, VCB, AND 75% OF VCB COMPARATORS 50µA TEMP COMPENSATED CURRENT SOURCE RINT 2kΩ VBG (1.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection CLOAD = 100µF RLP = 75kΩ GND VIN 20V/div MAX5938 CIN = 100µF VEE 20V/div GND VLP 20V/div VGATE 1V/div GND VOUT 200mV/div 40ms/div 4ms/div Figure 2. GATE Voltage Clamp During Power-Up Figure 3. Load-Probe Test During Initial Power-Up VIN 50V/div VIN 50V/div VGATE 10V/div VGATE 10V/div VOUT 50V/div VOUT 50V/div VPGOOD 50V/div VPGOOD 50V/div IIN 2A/div IIN 2A/div 40ms/div 40ms/div Figure 4.
MAX5938 -48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection the load. The short-circuit threshold voltage, V SC, is twice VCB (VSC = 2 x VCB) and is set by adjusting the resistance between CB_ADJ and VEE. There is an internal 2kΩ precision-trimmed resistor and an internal 50µA current source at CB_ADJ, which results in the minimum or default VSC of 100mV when CB_ADJ is connected to V EE .
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection • VOUT exceeds 74% of VCB during GATE ramp at 90% of full enhancement, VIN = (GND - VEE) GND R4 • VOUT exceeds the VCB for longer than 1.2ms during full enhancement, • VOUT exceeds the VSC during full enhancement, OFF R3 MAX5938 • Load-probe test fails, • VIN exceeds the programmed overvoltage (OV) limit for more than 1.5ms.
MAX5938 -48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection Disabling Circuit-Breaker and Short-Circuit Functions In the MAX5938, the circuit-breaker and short-circuit functions can be disabled, if desired, although this is not recommended. (See Warning note in the PGOOD Open-Drain Output section). This can be accomplished by leaving CB_ADJ open. In this case, PGOOD asserts 1.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection Output Voltage (VOUT) Slew-Rate Control OV, ON, and OFF provide an accurate means to set the overvoltage, turn-on, and turn-off voltage levels. All three are high-impedance inputs and by use of a 4-element resistor-divider from GND to VEE, the user can set an upper VEE threshold for triggering an overvoltage fault, a middle threshold for turning the part on, and a lower threshold for turning the part off.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection MAX5938 Applications Information VIN = (GND - VEE) Setting ON, OFF, and OV Voltage Levels The trip levels for ON, OFF, and OV can readily be set with a 4-element resistor-divider. Total resistance is a trade off of quiescent current, threshold tolerance due to pin input bias current (25nA), and the ability to follow very fast supply transients.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection 1) RTOT = R1 + R2 + R3 + R4 2) VOV,RISING = VREF x RTOT / R4 3) VOV,FALLING = VLO x RTOT / R4 4) VON,RISING = VREF x RTOT / (R3 + R4) 5) VON,FALLING = VLO x RTOT / (R3 + R4) 6) VOFF = VREF x RTOT / (R2 + R3 + R4) The resulting voltage levels are VOV,RISING = 79.82V ±2.5%, V OV,FALLING = 71.84V ±5%, V ON,RISING = 42.32V ±2.5%, VON,FALLING = 38.09V ±5%, and VOFF = 38.26V ±2.5%.
normalized units, typically with a value of 1 at +25°C, it is possible to multiply the curve by the drain voltage at +25°C and convert the curve to drain voltage. Now compare this curve to that of the MAX5938 normalized tempco of the circuit-breaker threshold to make a determination of the tracking error in mV between the power MOSFET [I D,MOSFET x R DS(ON) ] and the MAX5938 [ICB_ADJ (µA) x (2kΩ + RCB_ADJ)] over the operating temperature range of the application.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection MAX5938 GND FAULT MGT MAX5938 CSTEP_MON ISTEP_OS VSTEP_MON STEP_MON STEP_DET CYCLE GATE LOW ISTEP STEPTH ESL VIN STEP VSC RSTEP_MON SC TRIP CLOAD LOAD ESR C tCB_DLY VCB VEE GATE CB TRIP VOUT RDS,ON NOTE: VSC, VCB, VSTEPTH, VSTEP_MON, AND VOUT ARE REFERENCED TO VEE. Figure 16.
MAX5938 -48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection GND MAX5938 200mV LOAD OK TIMING LOGIC VIN Q1 LP VEE GATE VOUT ILOAD ITEST RLP CLOAD LOAD RON Figure 17. Load Probe Functional Diagram Appendix B gives a more complete analysis and discussion of the step monitor function. It provides methods for the characterization of the load response to a VIN ramp and graphical verification of the step monitor timing margins for a set of design parameters.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection SLEW RATE vs. CSLEW SLEW RATE (V/ms) 10 RLP = 36V x 90ms / (10,000µF x 220mV) = 1.472Ω ⇒ 1.47kΩ ±1% Next, evaluate the RLP at the maximum operating voltage to verify that it will not exceed the 1A current limit for the load-probe test. ITEST,MAX = VIN,MAX / RLP = 72V / 1.47kΩ = 49.0mA If the CLOAD(MAX) is increased to 190,000µF, the test current will approach the limit.
MAX5938 -48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection trol are in the linear range. If this is an issue, an external resistor, RGATE, in series with gate of the MOSFET is recommended to prevent possible oscillation. It should be as small as possible, e.g., 5Ω to 10Ω, to avoid impacting the MOSFET turn-off performance of the MAX5938.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection Step-to-Fault-Management Fault: 1) Same as step 1 above. [Step detection] 2) Same as step 2 above. [VOUT ramp] 2) Same as step 2 above. [GATE pulldown] 3) GATE ramps to 90% of full enhancement while VOUT remains above 74% VCB, at which point the GATE is rapidly pulled to VEE and fault management is initiated. [Fault management] 3) Same as step 3 above.
MAX5938 -48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection 3) When GATE reaches the gate threshold voltage of the power MOSFET, VOUT begins to ramp back down toward V EE. In the interval where GATE is below the MOSFET threshold, the MOSFET is off and VOUT will droop depending on the RC time constant of the load. [VOUT ramp] 4) When VOUT ramps below 74% VCB, the GATE is rapidly pulled to full enhancement and the OV GATE cycle is complete.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection VIN VIN = GND = VEE LEQU LOAD CAPACITOR WITH PARASITICS VIN RAMP where ILOAD is a function of the VOUT level that should be determined separately with DC tests. CLOAD 10V RDS,ON Figure 21. VIN Ramp Test Of Load VIN Verification of the Step Monitor Timing dv τ C dt dv dt VOUT.F VOUTi t1 t2 t3 t4 0 VIN RAMP Figure 22. General Response of VOUT to a VIN Ramp VOUT RESPONSE TO VIN RAMP OF 300V/ms 2.7 2.
At any time (t) the ∆VOUT fraction of ∆VOUT(max) is: ∆VOUT(t) / [(dV/dt) x τC] = (1-e(-t / τL,eqv)) If VOUT(t) is measured at time t, then the equivalent time constant of the load is found from: τL,eqv = -t / ln(1 – ∆VOUT / [(dV/dt) x τC]) As mentioned earlier, several measurements of ∆VOUT at times t1, t2, t3, and t4 should be made during the ramp. Each of these may result in slightly different values of τL,eqv and all values should then be averaged.
-48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection V+ GND (VIN = GND - VEE) VIN GND CLOAD MAX5938 PGOOD DC-DC CONVERTER ON V- OFF VOUT ON LP BACKPLANE OV STEP_MON * GATE POL_SEL CB_ADJ VEE ** -48V *OPTIONAL COMPONENT. **OPTIONAL COMPONENT REPLACED BY SHORT. Timing Table SYMBOL TYPICAL TIME (s) tONDLY 220m tLP 220m Load-Probe Retry Time tLP_OFF 3.5 PGOOD Assertion Delay Time tPGOOD 1.26m Autoretry Delay tRETRY 3.
Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) QSOP.EPS MAX5938 -48V Hot-Swap Controller with VIN Step Immunity, No RSENSE, and Overvoltage Protection PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH 21-0055 E 1 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product.
