Datasheet LTC1704, LTC1704B (Analog Devices) - 8

LTC1704/LTC1704B
U U U PI FU CTIO S
compensation and soft-start connections should return to
PGOOD (Pin 12):
Power Good. PGOOD is an open-drain GND. GND and PGND should connect only at a single logic output. PGOOD pulls low if any of the two supply point, near the PGND pin and the negative plate of the VIN outputs are outside ±10% of their nominal levels. An bypass capacitor. external pull-up resistor is required at PGOOD to allow it to swing positive.
REGFB (Pin 9):
Linear Regulator Controller Feedback Input. REGFB should be connected through a resistor
PGND (Pin 13):
Power Ground. The BG driver returns to divider network to VOUTREG to set the output voltage of the this pin. Connect PGND to a high current ground node in linear regulator. close proximity to the sources of external MOSFET QB, and the V
REGILM (Pin 10):
Linear Regulator Controller Current IN and VOUTSW bypass capacitors. Limit Setting cum ON/OFF Control. This pin is internally
BG (Pin 14):
Switcher Controller Bottom Gate Drive. The servoed to 0.8V. An external resistor RREGILM between VCC BG pin drives the gate of the bottom N-channel synchro- and REGILM programs the REGILM pin input current. This nous switch MOSFET, QB. BG is designed to typically drive current determines the maximum pass transistor base up to 10,000pF of gate capacitance. current and directly controls the linear regulator current
PV
sourcing capabilitiy. An external capacitor, C
CC (Pin 15):
Switcher Controller Bottom Gate Driver Sup- DELAY is added ply. PV to this pin to control the turn-on time of the linear regula- CC provides power to the BG output driver. PVCC must be connected to a voltage high enough to fully turn tor, the minimum value for this capacitor is 100pF. Refer on the external MOSFET, QB. PV to the Linear Regulator Current Limit Programming sec- CC should generally be con- nected directly to V tion for more information on choosing R IN, the main system 5V supply. PVCC REGILM and CDELAY. requires at least a 10µF bypass capacitor directly to PGND. Pulling REGILM to GND turns off the linear regulator. If both RUN/SS and REGILM are pulled low, the LTC1704
BOOST (Pin 16):
Switcher Controller Top Gate Driver enters shutdown mode. Supply. The BOOST pin supplies power to the floating TG driver. Bypass BOOST to SW with a 1µF capacitor. An
VCC (Pin 11):
Power Supply Input. All internal circuits external Schottky diode from V except the switcher output drivers are powered from this IN to BOOST creates a complete floating charge-pumped supply at BOOST. No pin. VCC should be connected to a low noise 5V supply, and other external supplies are required. should be bypassed to GND with at least a 10µF capacitor in close proximity to the LTC1704.
TEST CIRCUIT
5V + I I 1 16 BOOST PVCC IVCC 10µF f TG BOOST OSC 2 15 2000pF SW PVCC 3 14 IMAX LTC1704 BG RREGILM 4 13 2000pF 100k RUN/SS PGND 2k 5 12 COMP PGOOD 6 11 VFB FB VCC 7 10 REGDR REGILM 8 9 80k 100Ω GND REGFB 100pF 1704 TC 1µF 250k 1704bfa 8