LTC2977 datasheet(19/138 Pages) AD

19 / 138 page

LTM4664A

Rev. 0

For more information www.analog.com

PIN FUNCTIONS

4:1 Divider Section (Stage 1)

GND: (A8-A9, B1-B3, B8-B9, B14-B16, C4-C13,

D4,D8,D9, D13, E1-E4, E8-E9, E13-E16, F1-F4, F8-F10,

G4, G8-G11, H4, H9-H11, J1-J4, J11, K1-K4, K11, L3,

L11, L14-L16, M3-M5, M11, M14, N1-N4, N7, N11-N16,

P1-P4, P7-P9, P13-P15, R1-R6, R9, R13-16, T2-T3,

T8-T9, T14-T15) Main ground pins for all ground returns.

Input and output capacitors are connected to these pin.

See recommended layout Figure 45.

VOUT1: (C14-C16) 1st stage divide by two output

pins. These pins connect to the 2nd stage VINS2 pins.

Recommend placing output decoupling capacitance

directly between these pins and GND pins.

INTVCCS1: (D10) Output of the 5.5V internal linear low

dropout regulator. The driver and control circuits are pow-

ered from this voltage source. Must be bypassed to power

ground with a minimum of 4.7μF ceramic or other low ESR

capacitor. Do not use the INTVCCS1 pin for any other ICs.

EXTVCCS1: (D11) External Power Input to the Internal

LDO Connected to INTVCCS1. This LDO supplies INTVCCS1

power, bypassing the internal LDO powered from VINS1

whenever EXTVCCS1 is higher than 6.5V and VINS1 is

higher than 7V. Do not exceed 30V on this pin. This

pin can be driven with the VOUT2 output to limit power

loss in LDO with VINS1 at higher input voltage. See

Applications section.

PGOODS1: (D12) This is an open drain output pin.

PGOODS1 is pulled to ground if there are any faults or

the voltage at UVS1 pin is lower than 1V. Use PGOODS1

or FAULTS1 to sequence on RUNS2 for the second stage.

UVS1: (E10) Undervoltage Comparator. If the UVS1 pin

voltage is lower than 1V, the PGOODS1 pin is pulled down.

If the UV pin voltage is higher than 1V and no faults,

PGOODS1 pin is released. Connect to INTVCCS1 if not

used. This pin is used to validate proper output regulation.

FAULTS1: (E11) This is an open drain output pin. FAULTS1

is pulled to ground when the VOUT1 voltage is out of

the (VINS1)/2 window threshold or the voltage between

INSNSS1+ and INSNSS1– is higher than 50mV. FAULTS1

pin is released after INTVCCS1 starts up and passes UVLO.

Use FAULTS1 or PGOODS1 to sequence on RUNS2 for

the second stage.

FREQS1: (E12) Frequency Set Pin. There is a precision

10μA current flowing out of this pin. A resistor to ground

sets a voltage which in turn programs the frequency.

See the 4:1 Divider Application Information section for

detailed information.

RUNS1: (F11) Stage 1 Run Control Input. Forcing RUNS1

below 1.2V shuts down the controller. When RUNS1 is

higher than 1.2V, internal circuitry starts up. There is a

1μA pull-up current flowing out of RUNS1 pin when the

RUNS1 pin voltage is below 1.2V and an additional 5μA

current flowing out of RUNS1 pin when the RUNS1 pin

voltage is above 1.2V.

TIMERS1: (F12) Charge Balance and Fault Timer Control

Input. A capacitor between this pin and ground sets the

amount of time to charge VOUT1 to (VINS1)/2. It also sets

the short-circuit retry time. See the 4:1 Divider Application

Information.

HYS_PRGMS1: (G12) A resistor connected between

this pin and ground will set the window threshold of the

window comparator that monitors the voltage difference

between (VINS1)/2 and VOUT1. There is a 10μA current

flowing out of this pin. See Applications section.

SW1, SW2: (G14-G16), (D14-D16) Switching nodes for

the 1st stage CFLY Flying capacitor. See Block Diagram.

I INSNSS1–: (J13) Current sense comparator negative

input, connected to the negative node of the current sens-

ing resistor. Short to INSNSS1+ if not used.

NSNSS1+: (J14) Current sense comparator positive input,

connected to the positive node of the external current

sensing resistor. The current sensing resistor has to

be placed on the drain of the very top MOSFET. When

the voltage between INSNSS1+ pin and INSNSS1– pin

is higher than 50mV, the Stage 1 controller indicates

an overcurrent fault by pulling the FAULTS1 pin down.

The INSNSS1+ pin is also used to source 95mA current

to the VOUT1 pin during the pre-balance time in divider

applications. Connect directly to the drain of the very top

MOSFET if not used. See application schematic section.

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