Rainbow Electronics MAX5051 - Manual (Page 10)

MAX5051
Parallelable, Clamped Two-Switch
Power-Supply Controller IC
10 ______________________________________________________________________________________
Pin Description (continued)
PIN NAME FUNCTION
13 LXH
Synchronous-Pulse Transformer Driver, PMOS Open Drain. LXH is the high-side driver for the secondary-
side synchronous-pulse transformer. LXH can also drive a high-speed switching optocoupler. If not
used, connect LXH to LXVDD.
14 LXL
Synchronous-Pulse Transformer Driver, NMOS Open Drain. LXL is the low-side driver for the secondary-
side synchronous-pulse transformer. LXL can also drive a high-speed switching optocoupler. If not used,
connect LXL to PGND.
15 CS
Current-Sense Input. The current-limit threshold is internally set to 156mV relative to PGND. The device
has an internal noise filter. If necessary, connect an additional external RC filter.
16 DRVL
Gate-Drive Output for Low-Side MOSFET. DRVL is capable of sourcing and sinking approximately 2A
peak current.
17 PGND Power Ground
18 DRVDD
Supply Input for Low-Side MOSFET Driver. Bypass DRVDD locally with good quality 1µF || 0.1µF ceramic
capacitors. DRVDD is normally connected to REG9.
19 DRVB
Gate-Drive Output for Boost MOSFET. Connect the gate of a small high-voltage external FET to this pin to
enable charging of the high-side boost capacitor connected between pins 20 and 22. This FET may be
necessary to keep the boost capacitor charged at light loads.
20 XFRMRH Transformer Input. Transformer primary high-side connection.
21 DRVH Gate-Drive Output for High-Side MOSFET
22 BST
Boost Input. Boost supply connection point for the high-side MOSFET driver. Connect at least a 1µF ||
0.1µF ceramic capacitor from BST to XFRMRH with short and wide PC board traces. If the voltage across
the boost capacitor falls below the high-side undervoltage lockout threshold, the DRVH output stops
switching.
23 AVIN Supply Voltage Input. Connect AVIN directly to the input supply line.
24 GND Analog Signal Ground
25 UVLO
Undervoltage Lockout Input. An external voltage-divider from the input supply sets the startup voltage;
the threshold is 1.24V with 130mV hysteresis. UVLO can also be used as a shutdown input. If unused,
connect UVLO to REG5
26 STARTUP
Startup Input. STARTUP coordinates simultaneous startup of multiple units from faults, during initial turn-
on, and UVLO recovery. When paralleling the secondaries of two MAX5051’s, the STARTUP inputs of
each device must be connected together.
27 FLTINT
Faul t Integ r ati on Inp ut. D ur i ng p er si stent cur r ent- l i m i t faul ts, a cap aci tor connected to FLTIN T i s char g ed
w i th an i nter nal 90µA cur r ent sour ce. S w i tchi ng i s ter m i nated w hen the vol tag e r eaches 2.9V . An exter nal
r esi stor connected i n p ar al l el d i schar g es the cap aci tor . S w i tchi ng r esum es w hen the vol tag e d r op s to 2V .
28 SYNCIN
Synchronization Input. SYNCIN accepts the synchronization signal from SYNCOUT of another MAX5051
and shifts the switching of the synchronized unit by 180° allowing the reduction of input bypass
capacitors. The MAX5051 switches at the same frequency at SYNCIN. SYNCIN must be 50% duty cycle.
Leave SYNCIN floating if unused.